[Code of Federal Regulations]
[Title 40, Volume 2]
[Revised as of July 1, 2006]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR50.12]
[Page 9-121]
TITLE 40--PROTECTION OF ENVIRONMENT
CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
PART 50_NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS
--Table of Contents
Sec. 50.12 National primary and secondary ambient air quality standards
for lead.
National primary and secondary ambient air quality standards for
lead and its compounds, measured as elemental lead by a reference method
based on appendix G to this part, or by an equivalent method, are: 1.5
micrograms per cubic meter, maximum arithmetic mean averaged over a
calendar quarter.
(Secs. 109, 301(a) Clean Air Act as amended (42 U.S.C. 7409, 7601(a)))
[43 FR 46258, Oct. 5, 1978]
Appendix A to Part 50--Reference Method for the Determination of Sulfur
Dioxide in the Atmosphere (Pararosaniline Method)
1.0 Applicability.
1.1 This method provides a measurement of the concentration of
sulfur dioxide (SO2) in ambient air for determining
compliance with the primary and secondary national ambient air quality
standards for sulfur oxides (sulfur dioxide) as specified in Sec. 50.4
and Sec. 50.5 of this chapter. The method is applicable to the
measurement of ambient SO2 concentrations using sampling
periods ranging from 30 minutes to 24 hours. Additional quality
assurance procedures and guidance are provided in part 58, appendixes A
and B, of this chapter and in references 1 and 2.
2.0 Principle.
2.1 A measured volume of air is bubbled through a solution of 0.04 M
potassium tetrachloromercurate (TCM). The SO2 present in the
air stream reacts with the TCM solution to form a stable
monochlorosulfonatomercurate(3) complex. Once formed, this complex
resists air oxidation(4, 5) and is stable in the presence of strong
oxidants such as ozone and oxides of nitrogen. During subsequent
analysis, the complex is reacted with acid-bleached pararosaniline dye
and formaldehyde to form an intensely colored pararosaniline methyl
sulfonic acid.(6) The optical density of this species is determined
spectrophotometrically at 548 nm and is directly related to the amount
of SO2 collected. The total volume of air sampled, corrected
to EPA reference conditions (25 [deg]C, 760 mm Hg [101 kPa]), is
determined from the measured flow rate and the sampling time. The
concentration of SO2 in the ambient air is computed and
expressed in micrograms per standard cubic meter ([micro]g/std m\3\).
3.0 Range.
3.1 The lower limit of detection of SO2 in 10 mL of TCM
is 0.75 [micro]g (based on collaborative test results).(7) This
represents a concentration of 25 [micro]g SO2/m\3\ (0.01 ppm)
in an air sample of 30 standard liters (short-term sampling) and a
concentration of 13 [micro]g SO2/m\3\ (0.005 ppm) in an air
sample of 288 standard liters (long-term sampling). Concentrations less
than 25 [micro]g SO2/m\3\ can be measured by sampling larger
volumes of ambient air; however, the collection efficiency falls off
rapidly at low concentrations.(8, 9) Beer's law is adhered to up to 34
[micro]g of SO2 in 25 mL of final solution. This upper limit
of the analysis range represents a concentration of 1,130 [micro]g
SO2/m\3\ (0.43 ppm) in an air sample of 30 standard liters
and a concentration of 590 [micro]g SO2/m\3\ (0.23 ppm) in an
air sample of 288 standard liters. Higher concentrations can be measured
by collecting a smaller volume of air, by increasing the volume of
absorbing solution, or by diluting a suitable portion of
[[Page 10]]
the collected sample with absorbing solution prior to analysis.
4.0 Interferences.
4.1 The effects of the principal potential interferences have been
minimized or eliminated in the following manner: Nitrogen oxides by the
addition of sulfamic acid,(10, 11) heavy metals by the addition of
ethylenediamine tetracetic acid disodium salt (EDTA) and phosphoric
acid,(10, 12) and ozone by time delay.(10) Up to 60 [micro]g Fe (III),
22 [micro]g V (V), 10 [micro]g Cu (II), 10 [micro]g Mn (II), and 10
[micro]g Cr (III) in 10 mL absorbing reagent can be tolerated in the
procedure.(10) No significant interference has been encountered with 2.3
[micro]g NH3.(13)
5.0 Precision and Accuracy.
5.1 The precision of the analysis is 4.6 percent (at the 95 percent
confidence level) based on the analysis of standard sulfite samples.(10)
5.2 Collaborative test results (14) based on the analysis of
synthetic test atmospheres (SO2 in scrubbed air) using the
24-hour sampling procedure and the sulfite-TCM calibration procedure
show that:
The replication error varies linearly with
concentration from 2.5 [micro]g/m\3\ at
concentrations of 100 [micro]g/m\3\ to 7 [micro]g/
m\3\ at concentrations of 400 [micro]g/m\3\.
The day-to-day variability within an individual
laboratory (repeatability) varies linearly with concentration from
18.1 [micro]g/m\3\ at levels of 100 [micro]g/m\3\
to 50.9 [micro]g/m\3\ at levels of 400 [micro]g/
m\3\.
The day-to-day variability between two or more
laboratories (reproducibility) varies linearly with concentration from
36.9 [micro]g/m\3\ at levels of 100 [micro]g/m\3\
to 103.5 [micro] g/m\3\ at levels of 400 [micro]g/
m\3\.
The method has a concentration-dependent bias, which
becomes significant at the 95 percent confidence level at the high
concentration level. Observed values tend to be lower than the expected
SO2 concentration level.
6.0 Stability.
6.1 By sampling in a controlled temperature environment of
15[deg]10 [deg]C, greater than 98.9 percent of the
SO2-TCM complex is retained at the completion of sampling.
(15) If kept at 5 [deg]C following the completion of sampling, the
collected sample has been found to be stable for up to 30 days.(10) The
presence of EDTA enhances the stability of SO2 in the TCM
solution and the rate of decay is independent of the concentration of
SO2.(16)
7.0 Apparatus.
7.1 Sampling.
7.1.1 Sample probe: A sample probe meeting the requirements of
section 7 of 40 CFR part 58, appendix E (Teflon[reg] or glass
with residence time less than 20 sec.) is used to transport ambient air
to the sampling train location. The end of the probe should be designed
or oriented to preclude the sampling of precipitation, large particles,
etc. A suitable probe can be constructed from Teflon[reg]
tubing connected to an inverted funnel.
7.1.2 Absorber--short-term sampling: An all glass midget impinger
having a solution capacity of 30 mL and a stem clearance of 4 1 mm from the bottom of the vessel is used for sampling
periods of 30 minutes and 1 hour (or any period considerably less than
24 hours). Such an impinger is shown in Figure 1. These impingers are
commercially available from distributors such as Ace Glass,
Incorporated.
7.1.3 Absorber--24-hour sampling: A polypropylene tube 32 mm in
diameter and 164 mm long (available from Bel Art Products, Pequammock,
NJ) is used as the absorber. The cap of the absorber must be a
polypropylene cap with two ports (rubber stoppers are unacceptable
because the absorbing reagent can react with the stopper to yield
erroneously high SO2 concentrations). A glass impinger stem,
6 mm in diameter and 158 mm long, is inserted into one port of the
absorber cap. The tip of the stem is tapered to a small diameter orifice
(0.4 0.1 mm) such that a No. 79 jeweler's drill
bit will pass through the opening but a No. 78 drill bit will not.
Clearance from the bottom of the absorber to the tip of the stem must be
6 2 mm. Glass stems can be fabricated by any
reputable glass blower or can be obtained from a scientific supply firm.
Upon receipt, the orifice test should be performed to verify the orifice
size. The 50 mL volume level should be permanently marked on the
absorber. The assembled absorber is shown in Figure 2.
7.1.4 Moisture trap: A moisture trap constructed of a glass trap as
shown in Figure 1 or a polypropylene tube as shown in Figure 2 is placed
between the absorber tube and flow control device to prevent entrained
liquid from reaching the flow control device. The tube is packed with
indicating silica gel as shown in Figure 2. Glass wool may be
substituted for silica gel when collecting short-term samples (1 hour or
less) as shown in Figure 1, or for long term (24 hour) samples if flow
changes are not routinely encountered.
7.1.5 Cap seals: The absorber and moisture trap caps must seal
securely to prevent leaks during use. Heat-shrink material as shown in
Figure 2 can be used to retain the cap seals if there is any chance of
the caps coming loose during sampling, shipment, or storage.
[[Page 11]]
[[Page 12]]
7.1.6 Flow control device: A calibrated rotameter and needle valve
combination capable of maintaining and measuring air flow to within
2 percent is suitable for short-term sampling but
may not be used for long-term sampling. A critical orifice can be used
for regulating flow rate for both long-term and short-term sampling. A
22-gauge hypodermic
[[Page 13]]
needle 25 mm long may be used as a critical orifice to yield a flow rate
of approximately 1 L/min for a 30-minute sampling period. When sampling
for 1 hour, a 23-gauge hypodermic needle 16 mm in length will provide a
flow rate of approximately 0.5 L/min. Flow control for a 24-hour sample
may be provided by a 27-gauge hypodermic needle critical orifice that is
9.5 mm in length. The flow rate should be in the range of 0.18 to 0.22
L/min.
7.1.7 Flow measurement device: Device calibrated as specified in
9.4.1 and used to measure sample flow rate at the monitoring site.
7.1.8 Membrane particle filter: A membrane filter of 0.8 to 2
[micro]m porosity is used to protect the flow controller from particles
during long-term sampling. This item is optional for short-term
sampling.
7.1.9 Vacuum pump: A vacuum pump equipped with a vacuum gauge and
capable of maintaining at least 70 kPa (0.7 atm) vacuum differential
across the flow control device at the specified flow rate is required
for sampling.
7.1.10 Temperature control device: The temperature of the absorbing
solution during sampling must be maintained at 15[deg] 10 [deg]C. As soon as possible following sampling and
until analysis, the temperature of the collected sample must be
maintained at 5[deg] 5 [deg]C. Where an extended
period of time may elapse before the collected sample can be moved to
the lower storage temperature, a collection temperature near the lower
limit of the 15 10 [deg]C range should be used to
minimize losses during this period. Thermoelectric coolers specifically
designed for this temperature control are available commercially and
normally operate in the range of 5[deg] to 15 [deg]C. Small
refrigerators can be modified to provide the required temperature
control; however, inlet lines must be insulated from the lower
temperatures to prevent condensation when sampling under humid
conditions. A small heating pad may be necessary when sampling at low
temperatures (<7 [deg]C) to prevent the absorbing solution from
freezing.(17)
7.1.11 Sampling train container: The absorbing solution must be
shielded from light during and after sampling. Most commercially
available sampler trains are enclosed in a light-proof box.
7.1.12 Timer: A timer is recommended to initiate and to stop
sampling for the 24-hour period. The timer is not a required piece of
equipment; however, without the timer a technician would be required to
start and stop the sampling manually. An elapsed time meter is also
recommended to determine the duration of the sampling period.
7.2 Shipping.
7.2.1 Shipping container: A shipping container that can maintain a
temperature of 5[deg] 5 [deg]C is used for
transporting the sample from the collection site to the analytical
laboratory. Ice coolers or refrigerated shipping containers have been
found to be satisfactory. The use of eutectic cold packs instead of ice
will give a more stable temperature control. Such equipment is available
from Cole-Parmer Company, 7425 North Oak Park Avenue, Chicago, IL 60648.
7.3 Analysis.
7.3.1 Spectrophotometer: A spectrophotometer suitable for
measurement of absorbances at 548 nm with an effective spectral
bandwidth of less than 15 nm is required for analysis. If the
spectrophotometer reads out in transmittance, convert to absorbance as
follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.000
where:
A = absorbance, and
T = transmittance (0<=T<1).
A standard wavelength filter traceable to the National Bureau of
Standards is used to verify the wavelength calibration according to the
procedure enclosed with the filter. The wavelength calibration must be
verified upon initial receipt of the instrument and after each 160 hours
of normal use or every 6 months, whichever occurs first.
7.3.2 Spectrophotometer cells: A set of 1-cm path length cells
suitable for use in the visible region is used during analysis. If the
cells are unmatched, a matching correction factor must be determined
according to Section 10.1.
7.3.3 Temperature control device: The color development step during
analysis must be conducted in an environment that is in the range of
20[deg] to 30 [deg]C and controlled to 1 [deg]C.
Both calibration and sample analysis must be performed under identical
conditions (within 1 [deg]C). Adequate temperature control may be
obtained by means of constant temperature baths, water baths with manual
temperature control, or temperature controlled rooms.
7.3.4 Glassware: Class A volumetric glassware of various capacities
is required for preparing and standardizing reagents and standards and
for dispensing solutions during analysis. These included pipets,
volumetric flasks, and burets.
7.3.5 TCM waste receptacle: A glass waste receptacle is required for
the storage of spent TCM solution. This vessel should be stoppered and
stored in a hood at all times.
8.0 Reagents.
8.1 Sampling.
8.1.1 Distilled water: Purity of distilled water must be verified by
the following procedure:(18)
Place 0.20 mL of potassium permanganate solution
(0.316 g/L), 500 mL of distilled water, and 1mL of concentrated sulfuric
acid in a chemically resistant glass bottle, stopper the bottle, and
allow to stand.
[[Page 14]]
If the permanganate color (pink) does not disappear
completely after a period of 1 hour at room temperature, the water is
suitable for use.
If the permanganate color does disappear, the water
can be purified by redistilling with one crystal each of barium
hydroxide and potassium permanganate in an all glass still.
8.1.2 Absorbing reagent (0.04 M potassium tetrachloromercurate
[TCM]): Dissolve 10.86 g mercuric chloride, 0.066 g EDTA, and 6.0 g
potassium chloride in distilled water and dilute to volume with
distilled water in a 1,000-mL volumetric flask. (Caution: Mercuric
chloride is highly poisonous. If spilled on skin, flush with water
immediately.) The pH of this reagent should be between 3.0 and 5.0 (10)
Check the pH of the absorbing solution by using pH indicating paper or a
pH meter. If the pH of the solution is not between 3.0 and 5.0, dispose
of the solution according to one of the disposal techniques described in
Section 13.0. The absorbing reagent is normally stable for 6 months. If
a precipitate forms, dispose of the reagent according to one of the
procedures described in Section 13.0.
8.2 Analysis.
8.2.1 Sulfamic acid (0.6%): Dissolve 0.6 g sulfamic acid in 100 mL
distilled water. Perpare fresh daily.
8.2.2 Formaldehyde (0.2%): Dilute 5 mL formaldehyde solution (36 to
38 percent) to 1,000 mL with distilled water. Prepare fresh daily.
8.2.3 Stock iodine solution (0.1 N): Place 12.7 g resublimed iodine
in a 250-mL beaker and add 40 g potassium iodide and 25 mL water. Stir
until dissolved, transfer to a 1,000 mL volumetric flask and dilute to
volume with distilled water.
8.2.4 Iodine solution (0.01 N): Prepare approximately 0.01 N iodine
solution by diluting 50 mL of stock iodine solution (Section 8.2.3) to
500 mL with distilled water.
8.2.5 Starch indicator solution: Triturate 0.4 g soluble starch and
0.002 g mercuric iodide (preservative) with enough distilled water to
form a paste. Add the paste slowly to 200 mL of boiling distilled water
and continue boiling until clear. Cool and transfer the solution to a
glass stopperd bottle.
8.2.6 1 N hydrochloric acid: Slowly and while stirring, add 86 mL of
concentrated hydrochloric acid to 500 mL of distilled water. Allow to
cool and dilute to 1,000 mL with distilled water.
8.2.7 Potassium iodate solution: Accurately weigh to the nearest 0.1
mg, 1.5 g (record weight) of primary standard grade potassium iodate
that has been previously dried at 180 [deg]C for at least 3 hours and
cooled in a dessicator. Dissolve, then dilute to volume in a 500-mL
volumetric flask with distilled water.
8.2.8 Stock sodium thiosulfate solution (0.1 N): Prepare a stock
solution by dissolving 25 g sodium thiosulfate (Na2
S2 O3/5H2 O) in 1,000 mL freshly
boiled, cooled, distilled water and adding 0.1 g sodium carbonate to the
solution. Allow the solution to stand at least 1 day before
standardizing. To standardize, accurately pipet 50 mL of potassium
iodate solution (Section 8.2.7) into a 500-mL iodine flask and add 2.0 g
of potassium iodide and 10 mL of 1 N HCl. Stopper the flask and allow to
stand for 5 minutes. Titrate the solution with stock sodium thiosulfate
solution (Section 8.2.8) to a pale yellow color. Add 5 mL of starch
solution (Section 8.2.5) and titrate until the blue color just
disappears. Calculate the normality (Ns) of the stock sodium
thiosulfate solution as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.001
where:
M = volume of thiosulfate required in mL, and
W = weight of potassium iodate in g (recorded weight in Section 8.2.7).
[GRAPHIC] [TIFF OMITTED] TC08NO91.002
8.2.9 Working sodium thiosulfate titrant (0.01 N): Accurately pipet
100 mL of stock sodium thiosulfate solution (Section 8.2.8) into a
1,000-mL volumetric flask and dilute to volume with freshly boiled,
cooled, distilled water. Calculate the normality of the working sodium
thiosulfate titrant (NT) as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.003
8.2.10 Standardized sulfite solution for the preparation of working
sulfite-TCM solution: Dissolve 0.30 g sodium metabisulfite
(Na2 S2 O5) or 0.40 g sodium sulfite
(Na2 SO3) in 500 mL of recently boiled, cooled,
distilled water. (Sulfite solution is unstable; it is therefore
important to use water of the highest purity to minimize this
instability.) This solution contains the equivalent of 320 to 400
[micro]g SO2/mL. The actual concentration of the solution is
determined by adding excess iodine and back-titrating with standard
sodium thiosulfate solution. To back-titrate, pipet 50 mL of the 0.01 N
iodine solution (Section 8.2.4) into each of two 500-mL iodine flasks (A
and B). To flask A (blank) add 25 mL distilled water, and to flask B
(sample) pipet 25 mL sulfite solution. Stopper the flasks and allow to
stand for 5 minutes. Prepare the working sulfite-TCM solution (Section
8.2.11) immediately prior to adding the iodine solution to the flasks.
Using a buret containing standardized 0.01 N thiosulfate titrant
(Section 8.2.9), titrate the solution in each flask to a pale yellow
color. Then add 5
[[Page 15]]
mL starch solution (Section 8.2.5) and continue the titration until the
blue color just disappears.
8.2.11 Working sulfite-TCM solution: Accurately pipet 5 mL of the
standard sulfite solution (Section 8.2.10) into a 250-mL volumetric
flask and dilute to volume with 0.04 M TCM. Calculate the concentration
of sulfur dioxide in the working solution as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.004
where:
A = volume of thiosulfate titrant required for the blank, mL;
B = volume of thiosulfate titrant required for the sample, mL;
NT = normality of the thiosulfate titrant, from equation (3);
32,000 = milliequivalent weight of SO2, [micro]g;
25 = volume of standard sulfite solution, mL; and
0.02 = dilution factor.
This solution is stable for 30 days if kept at 5 [deg]C. (16) If not
kept at 5 [deg]C, prepare fresh daily.
8.2.12 Purified pararosaniline (PRA) stock solution (0.2% nominal):
8.2.12.1 Dye specifications--
The dye must have a maximum absorbance at a
wavelength of 540 nm when assayed in a buffered solution of 0.1 M sodium
acetate-acetic acid;
The absorbance of the reagent blank, which is
temperature sensitive (0.015 absorbance unit/ [deg]C), must not exceed
0.170 at 22 [deg]C with a 1-cm optical path length when the blank is
prepared according to the specified procedure;
The calibration curve (Section 10.0) must have a
slope equal to 0.030 0.002 absorbance unit/
[micro]g SO2 with a 1-cm optical path length when the dye is
pure and the sulfite solution is properly standardized.
8.2.12.2 Preparation of stock PRA solution--A specially purified (99
to 100 percent pure) solution of pararosaniline, which meets the above
specifications, is commercially available in the required 0.20 percent
concentration (Harleco Co.). Alternatively, the dye may be purified, a
stock solution prepared, and then assayed according to the procedure as
described below.(10)
8.2.12.3 Purification procedure for PRA--
1. Place 100 mL each of 1-butanol and 1 N HCl in a large separatory
funnel (250-mL) and allow to equilibrate. Note: Certain batches of 1-
butanol contain oxidants that create an SO2 demand. Before
using, check by placing 20 mL of 1-butanol and 5 mL of 20 percent
potassium iodide (KI) solution in a 50-mL separatory funnel and shake
thoroughly. If a yellow color appears in the alcohol phase, redistill
the 1-butanol from silver oxide and collect the middle fraction or
purchase a new supply of 1-butanol.
2. Weigh 100 mg of pararosaniline hydrochloride dye (PRA) in a small
beaker. Add 50 mL of the equilibrated acid (drain in acid from the
bottom of the separatory funnel in 1.) to the beaker and let stand for
several minutes. Discard the remaining acid phase in the separatory
funnel.
3. To a 125-mL separatory funnel, add 50 mL of the equilibrated 1-
butanol (draw the 1-butanol from the top of the separatory funnel in
1.). Transfer the acid solution (from 2.) containing the dye to the
funnel and shake carefully to extract. The violet impurity will transfer
to the organic phase.
4. Transfer the lower aqueous phase into another separatory funnel,
add 20 mL of equilibrated 1-butanol, and extract again.
5. Repeat the extraction procedure with three more 10-mL portions of
equilibrated 1-butanol.
6. After the final extraction, filter the acid phase through a
cotton plug into a 50-mL volumetric flask and bring to volume with 1 N
HCl. This stock reagent will be a yellowish red.
7. To check the purity of the PRA, perform the assay and adjustment
of concentration (Section 8.2.12.4) and prepare a reagent blank (Section
11.2); the absorbance of this reagent blank at 540 nm should be less
than 0.170 at 22 [deg]C. If the absorbance is greater than 0.170 under
these conditions, further extractions should be performed.
8.2.12.4 PRA assay procedure--The concentration of pararosaniline
hydrochloride (PRA) need be assayed only once after purification. It is
also recommended that commercial solutions of pararosaniline be assayed
when first purchased. The assay procedure is as follows:(10)
1. Prepare 1 M acetate-acetic acid buffer stock solution with a pH
of 4.79 by dissolving 13.61 g of sodium acetate trihydrate in distilled
water in a 100-mL volumetric flask. Add 5.70 mL of glacial acetic acid
and dilute to volume with distilled water.
2. Pipet 1 mL of the stock PRA solution obtained from the
purification process or from a commercial source into a 100-mL
volumetric flask and dilute to volume with distilled water.
[[Page 16]]
3. Transfer a 5-mL aliquot of the diluted PRA solution from 2. into
a 50-mL volumetric flask. Add 5mL of 1 M acetate-acetic acid buffer
solution from 1. and dilute the mixture to volume with distilled water.
Let the mixture stand for 1 hour.
4. Measure the absorbance of the above solution at 540 nm with a
spectrophotometer against a distilled water reference. Compute the
percentage of nominal concentration of PRA by
[GRAPHIC] [TIFF OMITTED] TC08NO91.005
where:
A = measured absorbance of the final mixture (absorbance units);
W = weight in grams of the PRA dye used in the assay to prepare 50 mL of
stock solution (for example, 0.100 g of dye was used to prepare 50 mL of
solution in the purification procedure; when obtained from commercial
sources, use the stated concentration to compute W; for 98% PRA, W=.098
g.); and
K = 21.3 for spectrophotometers having a spectral bandwidth of less than
15 nm and a path length of 1 cm.
8.2.13 Pararosaniline reagent: To a 250-mL volumetric flask, add 20
mL of stock PRA solution. Add an additional 0.2 mL of stock solution for
each percentage that the stock assays below 100 percent. Then add 25 mL
of 3 M phosphoric acid and dilute to volume with distilled water. The
reagent is stable for at least 9 months. Store away from heat and light.
9.0 Sampling Procedure.
9.1 General Considerations. Procedures are described for short-term
sampling (30-minute and 1-hour) and for long-term sampling (24-hour).
Different combinations of absorbing reagent volume, sampling rate, and
sampling time can be selected to meet special needs. For combinations
other than those specifically described, the conditions must be adjusted
so that linearity is maintained between absorbance and concentration
over the dynamic range. Absorbing reagent volumes less than 10 mL are
not recommended. The collection efficiency is above 98 percent for the
conditions described; however, the efficiency may be substantially lower
when sampling concentrations below 25 [micro][gamma]SO2/
m\3\.(8,9)
9.2 30-Minute and 1-Hour Sampling. Place 10 mL of TCM absorbing
reagent in a midget impinger and seal the impinger with a thin film of
silicon stopcock grease (around the ground glass joint). Insert the
sealed impinger into the sampling train as shown in Figure 1, making
sure that all connections between the various components are leak tight.
Greaseless ball joint fittings, heat shrinkable Teflon[reg]
tubing, or Teflon[reg] tube fittings may be used to attain
leakfree conditions for portions of the sampling train that come into
contact with air containing SO2. Shield the absorbing reagent
from direct sunlight by covering the impinger with aluminum foil or by
enclosing the sampling train in a light-proof box. Determine the flow
rate according to Section 9.4.2. Collect the sample at 1 0.10 L/min for 30-minute sampling or 0.500 0.05 L/min for 1-hour sampling. Record the exact
sampling time in minutes, as the sample volume will later be determined
using the sampling flow rate and the sampling time. Record the
atmospheric pressure and temperature.
9.3 24-Hour Sampling. Place 50 mL of TCM absorbing solution in a
large absorber, close the cap, and, if needed, apply the heat shrink
material as shown in Figure 3. Verify that the reagent level is at the
50 mL mark on the absorber. Insert the sealed absorber into the sampling
train as shown in Figure 2. At this time verify that the absorber
temperature is controlled to 15 10 [deg]C. During
sampling, the absorber temperature must be controlled to prevent
decomposition of the collected complex. From the onset of sampling until
analysis, the absorbing solution must be protected from direct sunlight.
Determine the flow rate according to Section 9.4.2. Collect the sample
for 24 hours from midnight to midnight at a flow rate of 0.200 0.020 L/min. A start/stop timer is helpful for
initiating and stopping sampling and an elapsed time meter will be
useful for determining the sampling time.
[[Page 17]]
9.4 Flow Measurement.
9.4.1 Calibration: Flow measuring devices used for the on-site flow
measurements required in 9.4.2 must be calibrated against a reliable
flow or volume standard such as an NBS traceable bubble flowmeter or
calibrated wet test meter. Rotameters or critical orifices used in the
sampling train may be calibrated, if desired, as a quality control
check, but such calibration shall not replace the on-site flow
measurements required by 9.4.2. In-line rotameters, if they are to be
calibrated, should be calibrated in situ, with the appropriate volume of
solution in the absorber.
9.4.2 Determination of flow rate at sampling site: For short-term
samples, the standard flow rate is determined at the sampling site at
the initiation and completion of sample collection with a calibrated
flow measuring device connected to the inlet of the absorber. For 24-
hour samples, the standard flow rate is determined at the time the
absorber is placed in the sampling train and again when the absorber is
removed from the train for shipment to the analytical laboratory with a
calibrated flow measuring device connected to the inlet of the sampling
train. The flow rate determination must be made with all components of
the sampling system in operation (e.g., the absorber temperature
controller and any sample box heaters must also be operating). Equation
6 may be used to determine the standard flow rate when a calibrated
positive displacement meter is used as the flow measuring device. Other
types of calibrated flow measuring devices may also be used to determine
the flow rate at the sampling site provided that the user applies any
appropriate corrections to devices for which output is dependent on
temperature or pressure.
[[Page 18]]
[GRAPHIC] [TIFF OMITTED] TC08NO91.006
where:
Qstd = flow rate at standard conditions, std L/min (25 [deg]C
and 760 mm Hg);
Qact = flow rate at monitoring site conditions, L/min;
Pb = barometric pressure at monitoring site conditions, mm Hg
or kPa;
RH = fractional relative humidity of the air being measured;
PH2O = vapor pressure of water at the temperature
of the air in the flow or volume standard, in the same units as
Pb, (for wet volume standards only, i.e., bubble flowmeter or
wet test meter; for dry standards, i.e., dry test meter,
PH2O=0);
Pstd = standard barometric pressure, in the same units as
Pb (760 mm Hg or 101 kPa); and
Tmeter = temperature of the air in the flow or volume
standard, [deg]C (e.g., bubble flowmeter).
If a barometer is not available, the following equation may be used
to determine the barometric pressure:
[GRAPHIC] [TIFF OMITTED] TC08NO91.007
where:
H = sampling site elevation above sea level in meters.
If the initial flow rate (Qi) differs from the flow rate
of the critical orifice or the flow rate indicated by the flowmeter in
the sampling train (Qc) by more than 5 percent as determined
by equation (8), check for leaks and redetermine Qi.
[GRAPHIC] [TIFF OMITTED] TC08NO91.008
Invalidate the sample if the difference between the initial
(Qi) and final (Qf) flow rates is more than 5
percent as determined by equation (9):
[GRAPHIC] [TIFF OMITTED] TC08NO91.009
9.5 Sample Storage and Shipment. Remove the impinger or absorber
from the sampling train and stopper immediately. Verify that the
temperature of the absorber is not above 25 [deg]C. Mark the level of
the solution with a temporary (e.g., grease pencil) mark. If the sample
will not be analyzed within 12 hours of sampling, it must be stored at
5[deg] 5 [deg]C until analysis. Analysis must
occur within 30 days. If the sample is transported or shipped for a
period exceeding 12 hours, it is recommended that thermal coolers using
eutectic ice packs, refrigerated shipping containers, etc., be used for
periods up to 48 hours. (17) Measure the temperature of the absorber
solution when the shipment is received. Invalidate the sample if the
temperature is above 10 [deg]C. Store the sample at 5[deg] 5 [deg]C until it is analyzed.
10.0 Analytical Calibration.
10.1 Spectrophotometer Cell Matching. If unmatched spectrophotometer
cells are used, an absorbance correction factor must be determined as
follows:
1. Fill all cells with distilled water and designate the one that
has the lowest absorbance at 548 nm as the reference. (This reference
cell should be marked as such and continually used for this purpose
throughout all future analyses.)
2. Zero the spectrophotometer with the reference cell.
3. Determine the absorbance of the remaining cells (Ac)
in relation to the reference cell and record these values for future
use. Mark all cells in a manner that adequately identifies the
correction.
The corrected absorbance during future analyses using each cell is
determining as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.010
where:
A = corrected absorbance,
Aobs = uncorrected absorbance, and
Ac = cell correction.
10.2 Static Calibration Procedure (Option 1). Prepare a dilute
working sulfite-TCM solution by diluting 10 mL of the working sulfite-
TCM solution (Section 8.2.11) to 100 mL with TCM absorbing reagent.
Following the table below, accurately pipet the indicated volumes of the
sulfite-TCM solutions into a series of 25-mL volumetric flasks. Add TCM
absorbing reagent as indicated to bring the volume in each flask to 10
mL.
[[Page 19]]
------------------------------------------------------------------------
Volume of Total
sulfite- Volume of [micro]g
Sulfite-TCM solution TCM TCM, mL SO2
solution (approx.*
------------------------------------------------------------------------
Working................................ 4.0 6.0 28.8
Working................................ 3.0 7.0 21.6
Working................................ 2.0 8.0 14.4
Dilute working......................... 10.0 0.0 7.2
Dilute working......................... 5.0 5.0 3.6
0.0 10.0 0.0
------------------------------------------------------------------------
*Based on working sulfite-TCM solution concentration of 7.2 [micro]g SO2/
mL; the actual total [micro]g SO2 must be calculated using equation 11
below.
To each volumetric flask, add 1 mL 0.6% sulfamic acid (Section
8.2.1), accurately pipet 2 mL 0.2% formaldehyde solution (Section
8.2.2), then add 5 mL pararosaniline solution (Section 8.2.13). Start a
laboratory timer that has been set for 30 minutes. Bring all flasks to
volume with recently boiled and cooled distilled water and mix
thoroughly. The color must be developed (during the 30-minute period) in
a temperature environment in the range of 20[deg] to 30 [deg]C, which is
controlled to 1 [deg]C. For increased precision, a
constant temperature bath is recommended during the color development
step. After 30 minutes, determine the corrected absorbance of each
standard at 548 nm against a distilled water reference (Section 10.1).
Denote this absorbance as (A). Distilled water is used in the reference
cell rather than the reagant blank because of the temperature
sensitivity of the reagent blank. Calculate the total micrograms
SO2 in each solution:
[GRAPHIC] [TIFF OMITTED] TC08NO91.011
where:
VTCM/SO2 = volume of sulfite-TCM solution used, mL;
CTCM/SO2 = concentration of sulfur dioxide in the working
sulfite-TCM, [micro]g SO2/mL (from equation 4); and
D = dilution factor (D = 1 for the working sulfite-TCM solution; D = 0.1
for the diluted working sulfite-TCM solution).
A calibration equation is determined using the method of linear
least squares (Section 12.1). The total micrograms SO2
contained in each solution is the x variable, and the corrected
absorbance (eq. 10) associated with each solution is the y variable. For
the calibration to be valid, the slope must be in the range of 0.030
0.002 absorbance unit/[micro]g SO2, the
intercept as determined by the least squares method must be equal to or
less than 0.170 absorbance unit when the color is developed at 22 [deg]C
(add 0.015 to this 0.170 specification for each [deg]C above 22 [deg]C)
and the correlation coefficient must be greater than 0.998. If these
criteria are not met, it may be the result of an impure dye and/or an
improperly standardized sulfite-TCM solution. A calibration factor
(Bs) is determined by calculating the reciprocal of the slope
and is subsequently used for calculating the sample concentration
(Section 12.3).
10.3 Dynamic Calibration Procedures (Option 2). Atmospheres
containing accurately known concentrations of sulfur dioxide are
prepared using permeation devices. In the systems for generating these
atmospheres, the permeation device emits gaseous SO2 at a
known, low, constant rate, provided the temperature of the device is
held constant (0.1 [deg]C) and the device has been
accurately calibrated at the temperature of use. The SO2
permeating from the device is carried by a low flow of dry carrier gas
to a mixing chamber where it is diluted with SO2-free air to
the desired concentration and supplied to a vented manifold. A typical
system is shown schematically in Figure 4 and this system and other
similar systems have been described in detail by O'Keeffe and Ortman;
(19) Scaringelli, Frey, and Saltzman, (20) and Scaringelli, O'Keeffe,
Rosenberg, and Bell. (21) Permeation devices may be prepared or
purchased and in both cases must be traceable either to a National
Bureau of Standards (NBS) Standard Reference Material (SRM 1625, SRM
1626, SRM 1627) or to an NBS/EPA-approved commercially available
Certified Reference Material (CRM). CRM's are described in Reference 22,
and a list of CRM sources is available from the address shown for
Reference 22. A recommended protocol for certifying a permeation device
to an NBS SRM or CRM is given in Section 2.0.7 of Reference 2. Device
permeation rates of 0.2 to 0.4 [micro]g/min, inert gas flows of about 50
mL/min, and dilution air flow rates from 1.1 to 15 L/min conveniently
yield standard atmospheres in the range of 25 to 600 [micro]g
SO2/m\3\ (0.010 to 0.230 ppm).
10.3.1 Calibration Option 2A (30-minute and 1-hour samples):
Generate a series of six standard atmospheres of SO2 (e.g.,
0, 50, 100, 200, 350, 500, 750 [micro]g/m\3\) by adjusting the dilution
flow rates appropriately. The concentration of SO2 in each
atmosphere is calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.014
where:
[[Page 20]]
Ca = concentration of SO2 at standard conditions,
[micro]g/m\3\;
Pr = permeation rate, [micro]g/min;
Qd = flow rate of dilution air, std L/min; and
Qp = flow rate of carrier gas across permeation device, std
L/min.
[[Page 21]]
Be sure that the total flow rate of the standard exceeds the flow
demand of the sample train, with the excess flow vented at atmospheric
pressure. Sample each atmosphere using similar apparatus as shown in
Figure 1 and under the same conditions as field sampling (i.e., use same
absorbing reagent volume and sample same volume of air at an equivalent
flow rate). Due to the length of the sampling periods required, this
method is not recommended for 24-hour sampling. At the completion of
sampling, quantitatively transfer the contents of each impinger to one
of a series of 25-mL volumetric flasks (if 10 mL of absorbing solution
was used) using small amounts of distilled water for rinse (<5mL). If
10 mL of absorbing solution was used, bring the absorber
solution in each impinger to orginal volume with distilled H2
O and pipet 10-mL portions from each impinger into a series of 25-mL
volumetric flasks. If the color development steps are not to be started
within 12 hours of sampling, store the solutions at 5[deg] 5 [deg]C. Calculate the total micrograms SO2
in each solution as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.015
where:
Ca = concentration of SO2 in the standard
atmosphere, [micro]g/m\3\;
Os = sampling flow rate, std L/min;
t=sampling time, min;
Va = volume of absorbing solution used for color development
(10 mL); and
Vb = volume of absorbing solution used for sampling, mL.
Add the remaining reagents for color development in the same manner
as in Section 10.2 for static solutions. Calculate a calibration
equation and a calibration factor (Bg) according to Section
10.2, adhering to all the specified criteria.
10.3.2 Calibration Option 2B (24-hour samples): Generate a standard
atmosphere containing approximately 1,050 [micro]g SO2/m\3\
and calculate the exact concentration according to equation 12. Set up a
series of six absorbers according to Figure 2 and connect to a common
manifold for sampling the standard atmosphere. Be sure that the total
flow rate of the standard exceeds the flow demand at the sample
manifold, with the excess flow vented at atmospheric pressure. The
absorbers are then allowed to sample the atmosphere for varying time
periods to yield solutions containing 0, 0.2, 0.6, 1.0, 1.4, 1.8, and
2.2 [micro]g SO2/mL solution. The sampling times required to
attain these solution concentrations are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.016
where:
t = sampling time, min;
Vb = volume of absorbing solution used for sampling (50 mL);
Cs = desired concentration of SO2 in the absorbing
solution, [micro]g/mL;
Ca = concentration of the standard atmosphere calculated
according to equation 12, [micro]g/m\3\; and
Qs = sampling flow rate, std L/min.
At the completion of sampling, bring the absorber solutions to
original volume with distilled water. Pipet a 10-mL portion from each
absorber into one of a series of 25-mL volumetric flasks. If the color
development steps are not to be started within 12 hours of sampling,
store the solutions at 5[deg] 5 [deg]C. Add the
remaining reagents for color development in the same manner as in
Section 10.2 for static solutions. Calculate the total [micro]g
SO2 in each standard as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.017
where:
Va = volume of absorbing solution used for color development
(10 mL).
All other parameters are defined in equation 14.
Calculate a calibration equation and a calibration factor
(Bt) according to Section 10.2 adhering to all the specified
criteria.
11.0 Sample Preparation and Analysis.
11.1 Sample Preparation. Remove the samples from the shipping
container. If the shipment period exceeded 12 hours from the completion
of sampling, verify that the temperature is below 10 [deg]C. Also,
compare the solution level to the temporary level mark on the absorber.
If either the temperature is above 10 [deg]C or there was significant
loss (more than 10 mL) of the sample during shipping, make an
appropriate notation in the record and invalidate the sample. Prepare
the samples for analysis as follows:
1. For 30-minute or 1-hour samples: Quantitatively transfer the
entire 10 mL amount of absorbing solution to a 25-mL volumetric flask
and rinse with a small amount (<5 mL) of distilled water.
2. For 24-hour samples: If the volume of the sample is less than the
original 50-mL volume (permanent mark on the absorber), adjust the
volume back to the original volume with distilled water to compensate
for water lost to evaporation during sampling. If the final volume is
greater than the original volume, the volume must be measured using a
graduated cylinder. To analyze, pipet 10 mL
[[Page 22]]
of the solution into a 25-mL volumetric flask.
11.2 Sample Analysis. For each set of determinations, prepare a
reagent blank by adding 10 mL TCM absorbing solution to a 25-mL
volumetric flask, and two control standards containing approximately 5
and 15 [micro]g SO2, respectively. The control standards are
prepared according to Section 10.2 or 10.3. The analysis is carried out
as follows:
1. Allow the sample to stand 20 minutes after the completion of
sampling to allow any ozone to decompose (if applicable).
2. To each 25-mL volumetric flask containing reagent blank, sample,
or control standard, add 1 mL of 0.6% sulfamic acid (Section 8.2.1) and
allow to react for 10 min.
3. Accurately pipet 2 mL of 0.2% formaldehyde solution (Section
8.2.2) and then 5 mL of pararosaniline solution (Section 8.2.13) into
each flask. Start a laboratory timer set at 30 minutes.
4. Bring each flask to volume with recently boiled and cooled
distilled water and mix thoroughly.
5. During the 30 minutes, the solutions must be in a temperature
controlled environment in the range of 20[deg] to 30 [deg]C maintained
to 1 [deg]C. This temperature must also be within
1 [deg]C of that used during calibration.
6. After 30 minutes and before 60 minutes, determine the corrected
absorbances (equation 10) of each solution at 548 nm using 1-cm optical
path length cells against a distilled water reference (Section 10.1).
(Distilled water is used as a reference instead of the reagent blank
because of the sensitivity of the reagent blank to temperature.)
7. Do not allow the colored solution to stand in the cells because a
film may be deposited. Clean the cells with isopropyl alcohol after use.
8. The reagent blank must be within 0.03 absorbance units of the
intercept of the calibration equation determined in Section 10.
11.3 Absorbance range. If the absorbance of the sample solution
ranges between 1.0 and 2.0, the sample can be diluted 1:1 with a portion
of the reagent blank and the absorbance redetermined within 5 minutes.
Solutions with higher absorbances can be diluted up to sixfold with the
reagent blank in order to obtain scale readings of less than 1.0
absorbance unit. However, it is recommended that a smaller portion (<10
mL) of the original sample be reanalyzed (if possible) if the sample
requires a dilution greater than 1:1.
11.4 Reaqent disposal. All reagents containing mercury compounds
must be stored and disposed of using one of the procedures contained in
Section 13. Until disposal, the discarded solutions can be stored in
closed glass containers and should be left in a fume hood.
12.0 Calculations.
12.1 Calibration Slope, Intercept, and Correlation Coefficient. The
method of least squares is used to calculate a calibration equation in
the form of:
[GRAPHIC] [TIFF OMITTED] TC08NO91.012
where:
y = corrected absorbance,
m = slope, absorbance unit/[micro]g SO2,
x = micrograms of SO2,
b = y intercept (absorbance units).
The slope (m), intercept (b), and correlation coefficient (r) are
calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.018
[GRAPHIC] [TIFF OMITTED] TR31AU93.019
[GRAPHIC] [TIFF OMITTED] TR31AU93.020
where n is the number of calibration points.
A data form (Figure 5) is supplied for easily organizing calibration
data when the slope, intercept, and correlation coefficient are
calculated by hand.
12.2 Total Sample Volume. Determine the sampling volume at standard
conditions as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.021
where:
Vstd = sampling volume in std L,
Qi = standard flow rate determined at the initiation of
sampling in std L/min,
Qf = standard flow rate determined at the completion of
sampling is std L/min, and
t = total sampling time, min.
12.3 Sulfur Dioxide Concentration. Calculate and report the
concentration of each sample as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.022
where:
A = corrected absorbance of the sample solution, from equation (10);
Ao = corrected absorbance of the reagent blank, using
equation (10);
BX = calibration factor equal to Bs,
Bg, or Bt depending on the calibration procedure
used, the reciprocal of the slope of the calibration equation;
Va = volume of absorber solution analyzed, mL;
Vb = total volume of solution in absorber (see 11.1-2), mL;
and
Vstd = standard air volume sampled, std L (from Section
12.2).
[[Page 23]]
Data Form
[For hand calculations]
----------------------------------------------------------------------------------------------------------------
Absor- bance
Calibration point no. Micro- grams So2 units
----------------------------------------------------------------------------------------------------------------
(x) (y) x\2\ xy y\2\
1............................. ................. ................. ................. ................ .....
2............................. ................. ................. ................. ................ .....
3............................. ................. ................. ................. ................ .....
4............................. ................. ................. ................. ................ .....
5............................. ................. ................. ................. ................ .....
6............................. ................. ................. ................. ................ .....
----------------------------------------------------------------------------------------------------------------
[Sigma] x=------ [Sigma] y=------ [Sigma] x\2\=------ [Sigma]xy------
[Sigma]y\2\------
n=------ (number of pairs of coordinates.)
[fxsp0]_________________________________________________________________
Figure 5. Data form for hand calculations.
12.4 Control Standards. Calculate the analyzed micrograms of
SO2 in each control standard as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.070
where:
Cq = analyzed [micro]g SO2 in each control
standard,
A = corrected absorbance of the control standard, and
Ao = corrected absorbance of the reagent blank.
The difference between the true and analyzed values of the control
standards must not be greater than 1 [micro]g. If the difference is
greater than 1 [micro]g, the source of the discrepancy must be
identified and corrected.
12.5 Conversion of [micro]g/m\3\ to ppm (v/v). If desired, the
concentration of sulfur dioxide at reference conditions can be converted
to ppm SO2 (v/v) as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.023
13.0 The TCM absorbing solution and any reagents containing mercury
compounds must be treated and disposed of by one of the methods
discussed below. Both methods remove greater than 99.99 percent of the
mercury.
13.1 Disposal of Mercury-Containing Solutions.
13.2 Method for Forming an Amalgam.
1. Place the waste solution in an uncapped vessel in a hood.
2. For each liter of waste solution, add approximately 10 g of
sodium carbonate until neutralization has occurred (NaOH may have to be
used).
3. Following neutralization, add 10 g of granular zinc or magnesium.
4. Stir the solution in a hood for 24 hours. Caution must be
exercised as hydrogen gas is evolved by this treatment process.
5. After 24 hours, allow the solution to stand without stirring to
allow the mercury amalgam (solid black material) to settle to the bottom
of the waste receptacle.
6. Upon settling, decant and discard the supernatant liquid.
7. Quantitatively transfer the solid material to a container and
allow to dry.
8. The solid material can be sent to a mercury reclaiming plant. It
must not be discarded.
13.3 Method Using Aluminum Foil Strips.
1. Place the waste solution in an uncapped vessel in a hood.
2. For each liter of waste solution, add approximately 10 g of
aluminum foil strips. If all the aluminum is consumed and no gas is
evolved, add an additional 10 g of foil. Repeat until the foil is no
longer consumed and allow the gas to evolve for 24 hours.
3. Decant the supernatant liquid and discard.
4. Transfer the elemental mercury that has settled to the bottom of
the vessel to a storage container.
5. The mercury can be sent to a mercury reclaiming plant. It must
not be discarded.
14.0 References for SO2 Method.
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume I, Principles. EPA-600/9-76-005, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711, 1976.
2. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume II, Ambient Air Specific Methods. EPA-600/4-77-027a, U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711, 1977.
3. Dasqupta, P. K., and K. B. DeCesare. Stability of Sulfur Dioxide
in Formaldehyde and Its Anomalous Behavior in Tetrachloromercurate (II).
Submitted for publication in Atmospheric Environment, 1982.
4. West, P. W., and G. C. Gaeke. Fixation of Sulfur Dioxide as
Disulfitomercurate (II) and Subsequent Colorimetric Estimation. Anal.
Chem., 28:1816, 1956.
5. Ephraim, F. Inorganic Chemistry. P. C. L. Thorne and E. R.
Roberts, Eds., 5th Edition, Interscience, 1948, p. 562.
6. Lyles, G. R., F. B. Dowling, and V. J. Blanchard. Quantitative
Determination of Formaldehyde in the Parts Per Hundred Million
Concentration Level. J. Air. Poll. Cont. Assoc., Vol. 15(106), 1965.
7. McKee, H. C., R. E. Childers, and O. Saenz, Jr. Collaborative
Study of Reference Method for Determination of Sulfur Dioxide in the
Atmosphere (Pararosaniline Method). EPA-APTD-0903, U.S. Environmental
Protection Agency, Research Triangle Park, NC 27711, September 1971.
8. Urone, P., J. B. Evans, and C. M. Noyes. Tracer Techniques in
Sulfur--Air Pollution Studies Apparatus and Studies of Sulfur Dioxide
Colorimetric and Conductometric Methods. Anal. Chem., 37: 1104, 1965.
[[Page 24]]
9. Bostrom, C. E. The Absorption of Sulfur Dioxide at Low
Concentrations (pphm) Studied by an Isotopic Tracer Method. Intern. J.
Air Water Poll., 9:333, 1965.
10. Scaringelli, F. P., B. E. Saltzman, and S. A. Frey.
Spectrophotometric Determination of Atmospheric Sulfur Dioxide. Anal.
Chem., 39: 1709, 1967.
11. Pate, J. B., B. E. Ammons, G. A. Swanson, and J. P. Lodge, Jr.
Nitrite Interference in Spectrophotometric Determination of Atmospheric
Sulfur Dioxide. Anal. Chem., 37:942, 1965.
12. Zurlo, N., and A. M. Griffini. Measurement of the Sulfur Dioxide
Content of the Air in the Presence of Oxides of Nitrogen and Heavy
Metals. Medicina Lavoro, 53:330, 1962.
13. Rehme, K. A., and F. P. Scaringelli. Effect of Ammonia on the
Spectrophotometric Determination of Atmospheric Concentrations of Sulfur
Dioxide. Anal. Chem., 47:2474, 1975.
14. McCoy, R. A., D. E. Camann, and H. C. McKee. Collaborative Study
of Reference Method for Determination of Sulfur Dioxide in the
Atmosphere (Pararosaniline Method) (24-Hour Sampling). EPA-650/4-74-027,
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711,
December 1973.
15. Fuerst, R. G. Improved Temperature Stability of Sulfur Dioxide
Samples Collected by the Federal Reference Method. EPA-600/4-78-018,
U.S. Environmental Protection Agency, Research Triangle Park, NC 27711,
April 1978.
16. Scaringelli, F. P., L. Elfers, D. Norris, and S. Hochheiser.
Enhanced Stability of Sulfur Dioxide in Solution. Anal. Chem., 42:1818,
1970.
17. Martin, B. E. Sulfur Dioxide Bubbler Temperature Study. EPA-600/
4-77-040, U.S. Environmental Protection Agency, Research Triangle Park,
NC 27711, August 1977.
18. American Society for Testing and Materials. ASTM Standards,
Water; Atmospheric Analysis. Part 23. Philadelphia, PA, October 1968, p.
226.
19. O'Keeffe, A. E., and G. C. Ortman. Primary Standards for Trace
Gas Analysis. Anal. Chem., 38:760, 1966.
20. Scaringelli, F. P., S. A. Frey, and B. E. Saltzman. Evaluation
of Teflon Permeation Tubes for Use with Sulfur Dioxide. Amer. Ind.
Hygiene Assoc. J., 28:260, 1967.
21. Scaringelli, F. P., A. E. O'Keeffe, E. Rosenberg, and J. P.
Bell, Preparation of Known Concentrations of Gases and Vapors With
Permeation Devices Calibrated Gravimetrically. Anal. Chem., 42:871,
1970.
22. A Procedure for Establishing Traceability of Gas Mixtures to
Certain National Bureau of Standards Standard Reference Materials. EPA-
600/7-81-010, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory (MD-77), Research Triangle Park, NC 27711,
January 1981.
[47 FR 54899, Dec. 6, 1982; 48 FR 17355, Apr. 22, 1983]
Appendix B to Part 50--Reference Method for the Determination of
Suspended Particulate Matter in the Atmosphere (High-Volume Method)
1.0 Applicability.
1.1 This method provides a measurement of the mass concentration of
total suspended particulate matter (TSP) in ambient air for determining
compliance with the primary and secondary national ambient air quality
standards for particulate matter as specified in Sec. 50.6 and Sec.
50.7 of this chapter. The measurement process is nondestructive, and the
size of the sample collected is usually adequate for subsequent chemical
analysis. Quality assurance procedures and guidance are provided in part
58, appendixes A and B, of this chapter and in References 1 and 2.
2.0 Principle.
2.1 An air sampler, properly located at the measurement site, draws
a measured quantity of ambient air into a covered housing and through a
filter during a 24-hr (nominal) sampling period. The sampler flow rate
and the geometry of the shelter favor the collection of particles up to
25-50 [micro]m (aerodynamic diameter), depending on wind speed and
direction.(3) The filters used are specified to have a minimum
collection efficiency of 99 percent for 0.3 [micro]m (DOP) particles
(see Section 7.1.4).
2.2 The filter is weighed (after moisture equilibration) before and
after use to determine the net weight (mass) gain. The total volume of
air sampled, corrected to EPA standard conditions (25 [deg]C, 760 mm Hg
[101 kPa]), is determined from the measured flow rate and the sampling
time. The concentration of total suspended particulate matter in the
ambient air is computed as the mass of collected particles divided by
the volume of air sampled, corrected to standard conditions, and is
expressed in micrograms per standard cubic meter ([micro]g/std m\3\).
For samples collected at temperatures and pressures significantly
different than standard conditions, these corrected concentrations may
differ substantially from actual concentrations (micrograms per actual
cubic meter), particularly at high elevations. The actual particulate
matter concentration can be calculated from the corrected concentration
using the actual temperature and pressure during the sampling period.
3.0 Range.
3.1 The approximate concentration range of the method is 2 to 750
[micro]g/std m\3\. The upper limit is determined by the point at which
the sampler can no longer maintain the specified
[[Page 25]]
flow rate due to the increased pressure drop of the loaded filter. This
point is affected by particle size distribution, moisture content of the
collected particles, and variability from filter to filter, among other
things. The lower limit is determined by the sensitivity of the balance
(see Section 7.10) and by inherent sources of error (see Section 6).
3.2 At wind speeds between 1.3 and 4.5 m/sec (3 and 10 mph), the
high-volume air sampler has been found to collect particles up to 25 to
50 [micro]m, depending on wind speed and direction.(3) For the filter
specified in Section 7.1, there is effectively no lower limit on the
particle size collected.
4.0 Precision.
4.1 Based upon collaborative testing, the relative standard
deviation (coefficient of variation) for single analyst precision
(repeatability) of the method is 3.0 percent. The corresponding value
for interlaboratory precision (reproducibility) is 3.7 percent.(4)
5.0 Accuracy.
5.1 The absolute accuracy of the method is undefined because of the
complex nature of atmospheric particulate matter and the difficulty in
determining the ``true'' particulate matter concentration. This method
provides a measure of particulate matter concentration suitable for the
purpose specified under Section 1.0, Applicability.
6.0 Inherent Sources of Error.
6.1 Airflow variation. The weight of material collected on the
filter represents the (integrated) sum of the product of the
instantaneous flow rate times the instantaneous particle concentration.
Therefore, dividing this weight by the average flow rate over the
sampling period yields the true particulate matter concentration only
when the flow rate is constant over the period. The error resulting from
a nonconstant flow rate depends on the magnitude of the instantaneous
changes in the flow rate and in the particulate matter concentration.
Normally, such errors are not large, but they can be greatly reduced by
equipping the sampler with an automatic flow controlling mechanism that
maintains constant flow during the sampling period. Use of a contant
flow controller is recommended.*
---------------------------------------------------------------------------
*At elevated altitudes, the effectiveness of automatic flow
controllers may be reduced because of a reduction in the maximum sampler
flow.
---------------------------------------------------------------------------
6.2 Air volume measurement. If the flow rate changes substantially
or nonuniformly during the sampling period, appreciable error in the
estimated air volume may result from using the average of the
presampling and postsampling flow rates. Greater air volume measurement
accuracy may be achieved by (1) equipping the sampler with a flow
controlling mechanism that maintains constant air flow during the
sampling period,* (2) using a calibrated, continuous flow rate recording
device to record the actual flow rate during the samping period and
integrating the flow rate over the period, or (3) any other means that
will accurately measure the total air volume sampled during the sampling
period. Use of a continuous flow recorder is recommended, particularly
if the sampler is not equipped with a constant flow controller.
6.3 Loss of volatiles. Volatile particles collected on the filter
may be lost during subsequent sampling or during shipment and/or storage
of the filter prior to the postsampling weighing.(5) Although such
losses are largely unavoidable, the filter should be reweighed as soon
after sampling as practical.
6.4 Artifact particulate matter. Artifact particulate matter can be
formed on the surface of alkaline glass fiber filters by oxidation of
acid gases in the sample air, resulting in a higher than true TSP
determination.(6 7) This effect usually occurs early in the sample
period and is a function of the filter pH and the presence of acid
gases. It is generally believed to account for only a small percentage
of the filter weight gain, but the effect may become more significant
where relatively small particulate weights are collected.
6.5 Humidity. Glass fiber filters are comparatively insensitive to
changes in relative humidity, but collected particulate matter can be
hygroscopic.(8) The moisture conditioning procedure minimizes but may
not completely eliminate error due to moisture.
6.6 Filter handling. Careful handling of the filter between the
presampling and postsampling weighings is necessary to avoid errors due
to loss of fibers or particles from the filter. A filter paper cartridge
or cassette used to protect the filter can minimize handling errors.
(See Reference 2, Section 2).
6.7 Nonsampled particulate matter. Particulate matter may be
deposited on the filter by wind during periods when the sampler is
inoperative. (9) It is recommended that errors from this source be
minimized by an automatic mechanical device that keeps the filter
covered during nonsampling periods, or by timely installation and
retrieval of filters to minimize the nonsampling periods prior to and
following operation.
6.8 Timing errors. Samplers are normally controlled by clock timers
set to start and stop the sampler at midnight. Errors in the nominal
1,440-min sampling period may result from a power interruption during
the sampling period or from a discrepancy between the start or stop time
recorded on the filter information record and the actual start or stop
time of the sampler. Such discrepancies may be caused by (1) poor
resolution of the timer set-points, (2) timer error due to power
interruption, (3) missetting of
[[Page 26]]
the timer, or (4) timer malfunction. In general, digital electronic
timers have much better set-point resolution than mechanical timers, but
require a battery backup system to maintain continuity of operation
after a power interruption. A continuous flow recorder or elapsed time
meter provides an indication of the sampler run-time, as well as
indication of any power interruption during the sampling period and is
therefore recommended.
6.9 Recirculation of sampler exhaust. Under stagnant wind
conditions, sampler exhaust air can be resampled. This effect does not
appear to affect the TSP measurement substantially, but may result in
increased carbon and copper in the collected sample. (10) This problem
can be reduced by ducting the exhaust air well away, preferably
downwind, from the sampler.
7.0 Apparatus.
(See References 1 and 2 for quality assurance information.)
Note: Samplers purchased prior to the effective date of this
amendment are not subject to specifications preceded by ([dagger]).
7.1 Filter. (Filters supplied by the Environmental Protection Agency
can be assumed to meet the following criteria. Additional specifications
are required if the sample is to be analyzed chemically.)
7.1.1 Size: 20.3 0.2 x 25.4 0.2 cm (nominal 8 x 10 in).
7.1.2 Nominal exposed area: 406.5 cm\2\ (63 in\2\).
7.1.3. Material: Glass fiber or other relatively inert,
nonhygroscopic material. (8)
7.1.4 Collection efficiency: 99 percent minimum as measured by the
DOP test (ASTM-2986) for particles of 0.3 [micro]m diameter.
7.1.5 Recommended pressure drop range: 42-54 mm Hg (5.6-7.2 kPa) at
a flow rate of 1.5 std m\3\/min through the nominal exposed area.
7.1.6 pH: 6 to 10. (11)
7.1.7 Integrity: 2.4 mg maximum weight loss. (11)
7.1.8 Pinholes: None.
7.1.9 Tear strength: 500 g minimum for 20 mm wide strip cut from
filter in weakest dimension. (See ASTM Test D828-60).
7.1.10 Brittleness: No cracks or material separations after single
lengthwise crease.
7.2 Sampler. The air sampler shall provide means for drawing the air
sample, via reduced pressure, through the filter at a uniform face
velocity.
7.2.1 The sampler shall have suitable means to:
a. Hold and seal the filter to the sampler housing.
b. Allow the filter to be changed conveniently.
c. Preclude leaks that would cause error in the measurement of the
air volume passing through the filter.
d. ([dagger]) Manually adjust the flow rate to accommodate
variations in filter pressure drop and site line voltage and altitude.
The adjustment may be accomplished by an automatic flow controller or by
a manual flow adjustment device. Any manual adjustment device must be
designed with positive detents or other means to avoid unintentional
changes in the setting.
---------------------------------------------------------------------------
([dagger]) See note at beginning of Section 7 of this appendix.
---------------------------------------------------------------------------
7.2.2 Minimum sample flow rate, heavily loaded filter: 1.1 m\3\/min
(39 ft\3\/min).[Dagger]
---------------------------------------------------------------------------
[Dagger] These specifications are in actual air volume units; to
convert to EPA standard air volume units, multiply the specifications by
(Pb/Pstd)(298/T) where Pb and T are the
barometric pressure in mm Hg (or kPa) and the temperature in K at the
sampler, and Pstd is 760 mm Hg (or 101 kPa).
---------------------------------------------------------------------------
7.2.3 Maximum sample flow rate, clean filter: 1.7 m\3\/min (60
ft\3\/min).[Dagger]
7.2.4 Blower Motor: The motor must be capable of continuous
operation for 24-hr periods.
7.3 Sampler shelter.
7.3.1 The sampler shelter shall:
a. Maintain the filter in a horizontal position at least 1 m above
the sampler supporting surface so that sample air is drawn downward
through the filter.
b. Be rectangular in shape with a gabled roof, similar to the design
shown in Figure 1.
c. Cover and protect the filter and sampler from precipitation and
other weather.
d. Discharge exhaust air at least 40 cm from the sample air inlet.
e. Be designed to minimize the collection of dust from the
supporting surface by incorporating a baffle between the exhaust outlet
and the supporting surface.
7.3.2 The sampler cover or roof shall overhang the sampler housing
somewhat, as shown in Figure 1, and shall be mounted so as to form an
air inlet gap between the cover and the sampler housing walls.
[dagger] This sample air inlet should be approximately
uniform on all sides of the sampler. [dagger] The area of the
sample air inlet must be sized to provide an effective particle capture
air velocity of between 20 and 35 cm/sec at the recommended operational
flow rate. The capture velocity is the sample air flow rate divided by
the inlet area measured in a horizontal plane at the lower edge of the
cover. [dagger] Ideally, the inlet area and operational flow
rate should be selected to obtain a capture air velocity of 25 2 cm/sec.
7.4 Flow rate measurement devices.
7.4.1 The sampler shall incorporate a flow rate measurement device
capable of indicating the total sampler flow rate. Two common types of
flow indicators covered in the calibration procedure are (1) an
electronic mass flowmeter and (2) an orifice or orifices
[[Page 27]]
located in the sample air stream together with a suitable pressure
indicator such as a manometer, or aneroid pressure gauge. A pressure
recorder may be used with an orifice to provide a continuous record of
the flow. Other types of flow indicators (including rotameters) having
comparable precision and accuracy are also acceptable.
7.4.2 [dagger] The flow rate measurement device must be capable of
being calibrated and read in units corresponding to a flow rate which is
readable to the nearest 0.02 std m\3\/min over the range 1.0 to 1.8 std
m\3\/min.
7.5 Thermometer, to indicate the approximate air temperature at the
flow rate measurement orifice, when temperature corrections are used.
7.5.1 Range: -40[deg] to +50 [deg]C (223-323 K).
7.5.2 Resolution: 2 [deg]C (2 K).
7.6 Barometer, to indicate barometric pressure at the flow rate
measurement orifice, when pressure corrections are used.
7.6.1 Range: 500 to 800 mm Hg (66-106 kPa).
7.6.2 Resolution: 5 mm Hg (0.67 kPa).
7.7 Timing/control device.
7.7.1 The timing device must be capable of starting and stopping the
sampler to obtain an elapsed run-time of 24 hr 1
hr (1,440 60 min).
7.7.2 Accuracy of time setting: 30 min, or
better. (See Section 6.8).
7.8 Flow rate transfer standard, traceable to a primary standard.
(See Section 9.2.)
7.8.1 Approximate range: 1.0 to 1.8 m\3\/min.
7.8.2 Resolution: 0.02 m\3\/min.
7.8.3 Reproducibility: 2 percent (2 times
coefficient of variation) over normal ranges of ambient temperature and
pressure for the stated flow rate range. (See Reference 2, Section 2.)
7.8.4 Maximum pressure drop at 1.7 std m\3\/min; 50 cm H2
O (5 kPa).
7.8.5 The flow rate transfer standard must connect without leaks to
the inlet of the sampler and measure the flow rate of the total air
sample.
7.8.6 The flow rate transfer standard must include a means to vary
the sampler flow rate over the range of 1.0 to 1.8 m\3\/min (35-64
ft\3\/min) by introducing various levels of flow resistance between the
sampler and the transfer standard inlet.
7.8.7 The conventional type of flow transfer standard consists of:
An orifice unit with adapter that connects to the inlet of the sampler,
a manometer or other device to measure orifice pressure drop, a means to
vary the flow through the sampler unit, a thermometer to measure the
ambient temperature, and a barometer to measure ambient pressure. Two
such devices are shown in Figures 2a and 2b. Figure 2a shows multiple
fixed resistance plates, which necessitate disassembly of the unit each
time the flow resistance is changed. A preferable design, illustrated in
Figure 2b, has a variable flow restriction that can be adjusted
externally without disassembly of the unit. Use of a conventional,
orifice-type transfer standard is assumed in the calibration procedure
(Section 9). However, the use of other types of transfer standards
meeting the above specifications, such as the one shown in Figure 2c,
may be approved; see the note following Section 9.1.
7.9 Filter conditioning environment
7.9.1 Controlled temperature: between 15[deg] and 30 [deg]C with
less than 3 [deg]C variation during equilibration
period.
7.9.2 Controlled humidity: Less than 50 percent relative humidity,
constant within 5 percent.
7.10 Analytical balance.
7.10.1 Sensitivity: 0.1 mg.
7.10.2 Weighing chamber designed to accept an unfolded 20.3x25.4 cm
(8x10 in) filter.
7.11 Area light source, similar to X-ray film viewer, to backlight
filters for visual inspection.
7.12 Numbering device, capable of printing identification numbers on
the filters before they are placed in the filter conditioning
environment, if not numbered by the supplier.
8.0 Procedure.
(See References 1 and 2 for quality assurance information.)
8.1 Number each filter, if not already numbered, near its edge with
a unique identification number.
8.2 Backlight each filter and inspect for pinholes, particles, and
other imperfections; filters with visible imperfections must not be
used.
8.3 Equilibrate each filter in the conditioning environment for at
least 24-hr.
8.4 Following equilibration, weigh each filter to the nearest
milligram and record this tare weight (Wi) with the filter
identification number.
8.5 Do not bend or fold the filter before collection of the sample.
8.6 Open the shelter and install a numbered, preweighed filter in
the sampler, following the sampler manufacturer's instructions. During
inclement weather, precautions must be taken while changing filters to
prevent damage to the clean filter and loss of sample from or damage to
the exposed filter. Filter cassettes that can be loaded and unloaded in
the laboratory may be used to minimize this problem (See Section 6.6).
8.7 Close the shelter and run the sampler for at least 5 min to
establish run-temperature conditions.
8.8 Record the flow indicator reading and, if needed, the barometric
pressure (P\3\3) and the ambient temperature
(T\3\3) see NOTE following step 8.12). Stop the sampler.
Determine the sampler flow rate (see Section 10.1); if it is outside the
acceptable range (1.1 to 1.7 m\3\/min [39-60 ft\3\/min]), use a
different filter, or adjust the sampler flow rate. Warning: Substantial
flow adjustments may affect the
[[Page 28]]
calibration of the orifice-type flow indicators and may necessitate
recalibration.
8.9 Record the sampler identification information (filter number,
site location or identification number, sample date, and starting time).
8.10 Set the timer to start and stop the sampler such that the
sampler runs 24-hrs, from midnight to midnight (local time).
8.11 As soon as practical following the sampling period, run the
sampler for at least 5 min to again establish run-temperature
conditions.
8.12 Record the flow indicator reading and, if needed, the
barometric pressure (P\3\3) and the ambient temperature
(T\3\3).
Note: No onsite pressure or temperature measurements are necessary
if the sampler flow indicator does not require pressure or temperature
corrections (e.g., a mass flowmeter) or if average barometric pressure
and seasonal average temperature for the site are incorporated into the
sampler calibration (see step 9.3.9). For individual pressure and
temperature corrections, the ambient pressure and temperature can be
obtained by onsite measurements or from a nearby weather station.
Barometric pressure readings obtained from airports must be station
pressure, not corrected to sea level, and may need to be corrected for
differences in elevation between the sampler site and the airport. For
samplers having flow recorders but not constant flow controllers, the
average temperature and pressure at the site during the sampling period
should be estimated from weather bureau or other available data.
8.13 Stop the sampler and carefully remove the filter, following the
sampler manufacturer's instructions. Touch only the outer edges of the
filter. See the precautions in step 8.6.
8.14 Fold the filter in half lengthwise so that only surfaces with
collected particulate matter are in contact and place it in the filter
holder (glassine envelope or manila folder).
8.15 Record the ending time or elapsed time on the filter
information record, either from the stop set-point time, from an elapsed
time indicator, or from a continuous flow record. The sample period must
be 1,440 60 min. for a valid sample.
8.16 Record on the filter information record any other factors, such
as meteorological conditions, construction activity, fires or dust
storms, etc., that might be pertinent to the measurement. If the sample
is known to be defective, void it at this time.
8.17 Equilibrate the exposed filter in the conditioning environment
for at least 24-hrs.
8.18 Immediately after equilibration, reweigh the filter to the
nearest milligram and record the gross weight with the filter
identification number. See Section 10 for TSP concentration
calculations.
9.0 Calibration.
9.1 Calibration of the high volume sampler's flow indicating or
control device is necessary to establish traceability of the field
measurement to a primary standard via a flow rate transfer standard.
Figure 3a illustrates the certification of the flow rate transfer
standard and Figure 3b illustrates its use in calibrating a sampler flow
indicator. Determination of the corrected flow rate from the sampler
flow indicator, illustrated in Figure 3c, is addressed in Section 10.1
Note: The following calibration procedure applies to a conventional
orifice-type flow transfer standard and an orifice-type flow indicator
in the sampler (the most common types). For samplers using a pressure
recorder having a square-root scale, 3 other acceptable calibration
procedures are provided in Reference 12. Other types of transfer
standards may be used if the manufacturer or user provides an
appropriately modified calibration procedure that has been approved by
EPA under Section 2.8 of appendix C to part 58 of this chapter.
9.2 Certification of the flow rate transfer standard.
9.2.1 Equipment required: Positive displacement standard volume
meter traceable to the National Bureau of Standards (such as a Roots
meter or equivalent), stop-watch, manometer, thermometer, and barometer.
9.2.2 Connect the flow rate transfer standard to the inlet of the
standard volume meter. Connect the manometer to measure the pressure at
the inlet of the standard volume meter. Connect the orifice manometer to
the pressure tap on the transfer standard. Connect a high-volume air
pump (such as a high-volume sampler blower) to the outlet side of the
standard volume meter. See Figure 3a.
9.2.3 Check for leaks by temporarily clamping both manometer lines
(to avoid fluid loss) and blocking the orifice with a large-diameter
rubber stopper, wide cellophane tape, or other suitable means. Start the
high-volume air pump and note any change in the standard volume meter
reading. The reading should remain constant. If the reading changes,
locate any leaks by listening for a whistling sound and/or retightening
all connections, making sure that all gaskets are properly installed.
9.2.4 After satisfactorily completing the leak check as described
above, unclamp both manometer lines and zero both manometers.
9.2.5 Achieve the appropriate flow rate through the system, either
by means of the variable flow resistance in the transfer standard or by
varying the voltage to the air pump. (Use of resistance plates as shown
in Figure 1a is discouraged because the above leak check must be
repeated each time a new resistance plate is installed.) At least five
different but constant flow rates, evenly distributed, with at least
three in the specified
[[Page 29]]
flow rate interval (1.1 to 1.7 m\3\/min [39-60 ft\3\/min]), are
required.
9.2.6 Measure and record the certification data on a form similar to
the one illustrated in Figure 4 according to the following steps.
9.2.7 Observe the barometric pressure and record as P1
(item 8 in Figure 4).
9.2.8 Read the ambient temperature in the vicinity of the standard
volume meter and record it as T1 (item 9 in Figure 4).
9.2.9 Start the blower motor, adjust the flow, and allow the system
to run for at least 1 min for a constant motor speed to be attained.
9.2.10 Observe the standard volume meter reading and simultaneously
start a stopwatch. Record the initial meter reading (Vi) in
column 1 of Figure 4.
9.2.11 Maintain this constant flow rate until at least 3 m\3\ of air
have passed through the standard volume meter. Record the standard
volume meter inlet pressure manometer reading as [Delta]P (column 5 in
Figure 4), and the orifice manometer reading as [Delta]H (column 7 in
Figure 4). Be sure to indicate the correct units of measurement.
9.2.12 After at least 3 m\3\ of air have passed through the system,
observe the standard volume meter reading while simultaneously stopping
the stopwatch. Record the final meter reading (Vf) in column
2 and the elapsed time (t) in column 3 of Figure 4.
9.2.13 Calculate the volume measured by the standard volume meter at
meter conditions of temperature and pressures as
Vm=Vf-Vi. Record in column 4 of Figure
4.
9.2.14 Correct this volume to standard volume (std m\3\) as follows:
[GRAPHIC] [TIFF OMITTED] TR31AU93.024
where:
Vstd = standard volume, std m\3\;
Vm = actual volume measured by the standard volume meter;
P1 = barometric pressure during calibration, mm Hg or kPa;
[Delta]P = differential pressure at inlet to volume meter, mm Hg or kPa;
Pstd = 760 mm Hg or 101 kPa;
Tstd = 298 K;
T1 = ambient temperature during calibration, K.
Calculate the standard flow rate (std m\3\/min) as follows:
[GRAPHIC] [TIFF OMITTED] TC08NO91.013
where:
Qstd = standard volumetric flow rate, std m\3\/min
t = elapsed time, minutes.
Record Qstd to the nearest 0.01 std m\3\/min in column 6
of Figure 4.
9.2.15 Repeat steps 9.2.9 through 9.2.14 for at least four
additional constant flow rates, evenly spaced over the approximate range
of 1.0 to 1.8 std m\3\/min (35-64 ft\3\/min).
9.2.16 For each flow, compute
[radic][Delta][Delta]H (P1/Pstd)(298/
T1)
(column 7a of Figure 4) and plot these value against Qstd as
shown in Figure 3a. Be sure to use consistent units (mm Hg or kPa) for
barometric pressure. Draw the orifice transfer standard certification
curve or calculate the linear least squares slope (m) and intercept (b)
of the certification curve:
[radic][Delta][Delta]H (P1/Pstd)(298/
T1)
=mQstd+b. See Figures 3 and 4. A certification graph should
be readable to 0.02 std m\3\/min.
9.2.17 Recalibrate the transfer standard annually or as required by
applicable quality control procedures. (See Reference 2.)
9.3 Calibration of sampler flow indicator.
Note: For samplers equipped with a flow controlling device, the flow
controller must be disabled to allow flow changes during calibration of
the sampler's flow indicator, or the alternate calibration of the flow
controller given in 9.4 may be used. For samplers using an orifice-type
flow indicator downstream of the motor, do not vary the flow rate by
adjusting the voltage or power supplied to the sampler.
9.3.1 A form similar to the one illustrated in Figure 5 should be
used to record the calibration data.
9.3.2 Connect the transfer standard to the inlet of the sampler.
Connect the orifice manometer to the orifice pressure tap, as
illustrated in Figure 3b. Make sure there are no leaks between the
orifice unit and the sampler.
9.3.3 Operate the sampler for at least 5 minutes to establish
thermal equilibrium prior to the calibration.
9.3.4 Measure and record the ambient temperature, T2, and
the barometric pressure, P2, during calibration.
9.3.5 Adjust the variable resistance or, if applicable, insert the
appropriate resistance plate (or no plate) to achieve the desired flow
rate.
9.3.6 Let the sampler run for at least 2 min to re-establish the
run-temperature conditions. Read and record the pressure drop across the
orifice ([Delta]H) and the sampler flow rate indication (I) in the
appropriate columns of Figure 5.
9.3.7 Calculate [radic][Delta][Delta]H(P2/
Pstd)(298/T2) and determine the flow rate at
standard conditions (Qstd) either graphically from the
certification curve or by calculating Qstd from the least
square slope and intercept of the transfer standard's transposed
certification curve: Qstd=1/m [radic][Delta]H(P2/
Pstd)(298/T2)-b. Record the value of
Qstd on Figure 5.
[[Page 30]]
9.3.8 Repeat steps 9.3.5, 9.3.6, and 9.3.7 for several additional
flow rates distributed over a range that includes 1.1 to 1.7 std m\3\/
min.
9.3.9 Determine the calibration curve by plotting values of the
appropriate expression involving I, selected from table 1, against
Qstd. The choice of expression from table 1 depends on the
flow rate measurement device used (see Section 7.4.1) and also on
whether the calibration curve is to incorporate geographic average
barometric pressure (Pa) and seasonal average temperature
(Ta) for the site to approximate actual pressure and
temperature. Where Pa and Ta can be determined for
a site for a seasonal period such that the actual barometric pressure
and temperature at the site do not vary by more than 60 mm Hg (8 kPa) from Pa or 15 [deg]C from Ta, respectively, then using
Pa and Ta avoids the need for subsequent pressure
and temperature calculation when the sampler is used. The geographic
average barometric pressure (Pa) may be estimated from an
altitude-pressure table or by making an (approximate) elevation
correction of -26 mm Hg (-3.46 kPa) for each 305 m (1,000 ft) above sea
level (760 mm Hg or 101 kPa). The seasonal average temperature
(Ta) may be estimated from weather station or other records.
Be sure to use consistent units (mm Hg or kPa) for barometric pressure.
9.3.10 Draw the sampler calibration curve or calculate the linear
least squares slope (m), intercept (b), and correlation coefficient of
the calibration curve: [Expression from table 1]= mQstd+b.
See Figures 3 and 5. Calibration curves should be readable to 0.02 std
m\3\/min.
9.3.11 For a sampler equipped with a flow controller, the flow
controlling mechanism should be re-enabled and set to a flow near the
lower flow limit to allow maximum control range. The sample flow rate
should be verified at this time with a clean filter installed. Then add
two or more filters to the sampler to see if the flow controller
maintains a constant flow; this is particularly important at high
altitudes where the range of the flow controller may be reduced.
9.4 Alternate calibration of flow-controlled samplers. A flow-
controlled sampler may be calibrated solely at its controlled flow rate,
provided that previous operating history of the sampler demonstrates
that the flow rate is stable and reliable. In this case, the flow
indicator may remain uncalibrated but should be used to indicate any
relative change between initial and final flows, and the sampler should
be recalibrated more often to minimize potential loss of samples because
of controller malfunction.
9.4.1 Set the flow controller for a flow near the lower limit of the
flow range to allow maximum control range.
9.4.2 Install a clean filter in the sampler and carry out steps
9.3.2, 9.3.3, 9.3.4, 9.3.6, and 9.3.7.
9.4.3 Following calibration, add one or two additional clean filters
to the sampler, reconnect the transfer standard, and operate the sampler
to verify that the controller maintains the same calibrated flow rate;
this is particularly important at high altitudes where the flow control
range may be reduced.
[[Page 31]]
10.0 Calculations of TSP Concentration.
10.1 Determine the average sampler flow rate during the sampling
period according to either 10.1.1 or 10.1.2 below.
10.1.1 For a sampler without a continuous flow recorder, determine
the appropriate expression to be used from table 2 corresponding to the
one from table 1 used in step 9.3.9. Using this appropriate expression,
determine Qstd for the initial flow rate from the sampler
calibration curve, either graphically or from the transposed regression
equation:
Qstd =
1/m ([Appropriate expression from table 2]-b)
Similarly, determine Qstd from the final flow reading, and
calculate the average flow Qstd as one-half the sum of the
initial and final flow rates.
10.1.2 For a sampler with a continuous flow recorder, determine the
average flow rate device reading, I, for the period. Determine the
appropriate expression from table 2 corresponding to the one from table
1 used in step 9.3.9. Then using this expression and the average flow
rate reading, determine Qstd from the sampler calibration
curve, either graphically or from the transposed regression equation:
Qstd =
1/m ([Appropriate expression from table 2]-b)
If the trace shows substantial flow change during the sampling
period, greater accuracy may be achieved by dividing the sampling period
into intervals and calculating an average reading before determining
Qstd.
10.2 Calculate the total air volume sampled as:
V-Qstdx t
where:
V = total air volume sampled, in standard volume units, std m\3\/;
Qstd = average standard flow rate, std m\3\/min;
t = sampling time, min.
10.3 Calculate and report the particulate matter concentration as:
[GRAPHIC] [TIFF OMITTED] TR31AU93.025
where:
TSP = mass concentration of total suspended particulate matter,
[micro]g/std m\3\;
Wi = initial weight of clean filter, g;
Wf = final weight of exposed filter, g;
V = air volume sampled, converted to standard conditions, std m\3\,
10\6\ = conversion of g to [micro]g.
10.4 If desired, the actual particulate matter concentration (see
Section 2.2) can be calculated as follows:
(TSP)a=TSP (P3/Pstd)(298/T3)
where:
(TSP)a = actual concentration at field conditions, [micro]g/
m\3\;
[[Page 32]]
TSP = concentration at standard conditions, [micro]g/std m\3\;
P3 = average barometric pressure during sampling period, mm
Hg;
Pstd = 760 mn Hg (or 101 kPa);
T3 = average ambient temperature during sampling period, K.
11.0 References.
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume I, Principles. EPA-600/9-76-005, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711, 1976.
2. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume II, Ambient Air Specific Methods. EPA-600/4-77-027a, U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711, 1977.
3. Wedding, J. B., A. R. McFarland, and J. E. Cernak. Large Particle
Collection Characteristics of Ambient Aerosol Samplers. Environ. Sci.
Technol. 11:387-390, 1977.
4. McKee, H. C., et al. Collaborative Testing of Methods to Measure
Air Pollutants, I. The High-Volume Method for Suspended Particulate
Matter. J. Air Poll. Cont. Assoc., 22 (342), 1972.
5. Clement, R. E., and F. W. Karasek. Sample Composition Changes in
Sampling and Analysis of Organic Compounds in Aerosols. The Intern. J.
Environ. Anal. Chem., 7:109, 1979.
6. Lee, R. E., Jr., and J. Wagman. A Sampling Anomaly in the
Determination of Atmospheric Sulfuric Concentration. Am. Ind. Hygiene
Assoc. J., 27:266, 1966.
7. Appel, B. R., et al. Interference Effects in Sampling Particulate
Nitrate in Ambient Air. Atmospheric Environment, 13:319, 1979.
8. Tierney, G. P., and W. D. Conner. Hygroscopic Effects on Weight
Determinations of Particulates Collected on Glass-Fiber Filters. Am.
Ind. Hygiene Assoc. J., 28:363, 1967.
9. Chahal, H. S., and D. J. Romano. High-Volume Sampling Effect of
Windborne Particulate Matter Deposited During Idle Periods. J. Air Poll.
Cont. Assoc., Vol. 26 (885), 1976.
10. Patterson, R. K. Aerosol Contamination from High-Volume Sampler
Exhaust. J. Air Poll. Cont. Assoc., Vol. 30 (169), 1980.
11. EPA Test Procedures for Determining pH and Integrity of High-
Volume Air Filters. QAD/M-80.01. Available from the Methods
Standardization Branch, Quality Assurance Division, Environmental
Monitoring Systems Laboratory (MD-77), U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711, 1980.
12. Smith, F., P. S. Wohlschlegel, R. S. C. Rogers, and D. J.
Mulligan. Investigation of Flow Rate Calibration Procedures Associated
with the High-Volume Method for Determination of Suspended Particulates.
EPA-600/4-78-047, U.S. Environmental Protection Agency, Research
Triangle Park, NC, June 1978.
[[Page 33]]
[[Page 34]]
[[Page 35]]
[[Page 36]]
[47 FR 54912, Dec. 6, 1982; 48 FR 17355, Apr. 22, 1983]
Appendix C to Part 50--Measurement Principle and Calibration Procedure
for the Measurement of Carbon Monoxide in the Atmosphere (Non-Dispersive
Infrared Photometry)
Measurement Principle
1. Measurements are based on the absorption of infrared radiation by
carbon monoxide (CO) in a non-dispersive photometer. Infrared energy
from a source is passed through a cell containing the gas sample to be
analyzed, and the quantitative absorption of energy by CO in the sample
cell is measured by a suitable detector. The photometer is sensitized to
CO by employing CO gas in either the detector or in a filter cell in the
optical path, thereby limiting the measured absorption to one or more of
the characteristic wavelengths at which CO strongly absorbs. Optical
filters or other means may
[[Page 37]]
also be used to limit sensitivity of the photometer to a narrow band of
interest. Various schemes may be used to provide a suitable zero
reference for the photometer. The measured absorption is converted to an
electrical output signal, which is related to the concentration of CO in
the measurement cell.
2. An analyzer based on this principle will be considered a
reference method only if it has been designated as a reference method in
accordance with part 53 of this chapter.
3. Sampling considerations.
The use of a particle filter on the sample inlet line of an NDIR CO
analyzer is optional and left to the discretion of the user or the
manufacturer. Use of filter should depend on the analyzer's
susceptibility to interference, malfunction, or damage due to particles.
Calibration Procedure
1. Principle. Either of two methods may be used for dynamic
multipoint calibration of CO analyzers:
(1) One method uses a single certified standard cylinder of CO,
diluted as necessary with zero air, to obtain the various calibration
concentrations needed.
(2) The other method uses individual certified standard cylinders of
CO for each concentration needed. Additional information on calibration
may be found in Section 2.0.9 of Reference 1.
2. Apparatus. The major components and typical configurations of the
calibration systems for the two calibration methods are shown in Figures
1 and 2.
2.1 Flow controller(s). Device capable of adjusting and regulating
flow rates. Flow rates for the dilution method (Figure 1) must be
regulated to 1%.
2.2 Flow meter(s). Calibrated flow meter capable of measuring and
monitoring flow rates. Flow rates for the dilution method (Figure 1)
must be measured with an accuracy of 2% of the
measured value.
2.3 Pressure regulator(s) for standard CO cylinder(s). Regulator
must have nonreactive diaphragm and internal parts and a suitable
delivery pressure.
2.4 Mixing chamber. A chamber designed to provide thorough mixing of
CO and diluent air for the dilution method.
2.5 Output manifold. The output manifold should be of sufficient
diameter to insure an insignificant pressure drop at the analyzer
connection. The system must have a vent designed to insure atmospheric
pressure at the manifold and to prevent ambient air from entering the
manifold.
3. Reagents.
3.1 CO concentration standard(s). Cylinder(s) of CO in air
containing appropriate concentrations(s) of CO suitable for the selected
operating range of the analyzer under calibration; CO standards for the
dilution method may be contained in a nitrogen matrix if the zero air
dilution ratio is not less than 100:1. The assay of the cylinder(s) must
be traceable either to a National Bureau of Standards (NBS) CO in air
Standard Reference Material (SRM) or to an NBS/EPA-approved commercially
available Certified Reference Material (CRM). CRM's are described in
Reference 2, and a list of CRM sources is available from the address
shown for Reference 2. A recommended protocol for certifying CO gas
cylinders against either a CO SRM or a CRM is given in Reference 1. CO
gas cylinders should be recertified on a regular basis as determined by
the local quality control program.
3.2 Dilution gas (zero air). Air, free of contaminants which will
cause a detectable response on the CO analyzer. The zero air should
contain <0.1 ppm CO. A procedure for generating zero air is given in
Reference 1.
4. Procedure Using Dynamic Dilution Method.
4.1 Assemble a dynamic calibration system such as the one shown in
Figure 1. All calibration gases including zero air must be introduced
into the sample inlet of the analyzer system. For specific operating
instructions refer to the manufacturer's manual.
4.2 Insure that all flowmeters are properly calibrated, under the
conditions of use, if appropriate, against an authoritative standard
such as a soap-bubble meter or wet-test meter. All volumetric flowrates
should be corrected to 25 [deg]C and 760 mm Hg (101 kPa). A discussion
on calibration of flowmeters is given in Reference 1.
4.3 Select the operating range of the CO analyzer to be calibrated.
4.4 Connect the signal output of the CO analyzer to the input of the
strip chart recorder or other data collection device. All adjustments to
the analyzer should be based on the appropriate strip chart or data
device readings. References to analyzer responses in the procedure given
below refer to recorder or data device responses.
4.5 Adjust the calibration system to deliver zero air to the output
manifold. The total air flow must exceed the total demand of the
analyzer(s) connected to the output manifold to insure that no ambient
air is pulled into the manifold vent. Allow the analyzer to sample zero
air until a stable respose is obtained. After the response has
stabilized, adjust the analyzer zero control. Offsetting the analyzer
zero adjustments to +5 percent of scale is recommended to facilitate
observing negative zero drift. Record the stable zero air response as
ZCO.
4.6 Adjust the zero air flow and the CO flow from the standard CO
cylinder to provide a diluted CO concentration of approximately 80
percent of the upper range limit (URL) of the operating range of the
analyzer. The total air flow must exceed the total demand of the
analyzer(s) connected to the output manifold to insure that no ambient
air is
[[Page 38]]
pulled into the manifold vent. The exact CO concentration is calculated
from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.026
where:
[CO]OUT = diluted CO concentration at the output manifold,
ppm;
[CO]STD = concentration of the undiluted CO standard, ppm;
FCO = flow rate of the CO standard corrected to 25 [deg]C and
760 mm Hg, (101 kPa), L/min; and
FD = flow rate of the dilution air corrected to 25 [deg]C and
760 mm Hg, (101 kPa), L/min.
Sample this CO concentration until a stable response is obtained.
Adjust the analyzer span control to obtain a recorder response as
indicated below:
Recorder response (percent scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.027
where:
URL = nominal upper range limit of the analyzer's operating range, and
ZCO = analyzer response to zero air, % scale.
If substantial adjustment of the analyzer span control is required,
it may be necessary to recheck the zero and span adjustments by
repeating Steps 4.5 and 4.6. Record the CO concentration and the
analyzer's response. 4.7 Generate several additional concentrations (at
least three evenly spaced points across the remaining scale are
suggested to verify linearity) by decreasing FCO or
increasing FD. Be sure the total flow exceeds the analyzer's
total flow demand. For each concentration generated, calculate the exact
CO concentration using Equation (1). Record the concentration and the
analyzer's response for each concentration. Plot the analyzer responses
versus the corresponding CO concentrations and draw or calculate the
calibration curve.
5. Procedure Using Multiple Cylinder Method. Use the procedure for
the dynamic dilution method with the following changes:
5.1 Use a multi-cylinder system such as the typical one shown in
Figure 2.
5.2 The flowmeter need not be accurately calibrated, provided the
flow in the output manifold exceeds the analyzer's flow demand.
5.3 The various CO calibration concentrations required in Steps 4.6
and 4.7 are obtained without dilution by selecting the appropriate
certified standard cylinder.
References
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume II--Ambient Air Specific Methods, EPA-600/4-77-027a, U.S.
Environmental Protection Agency, Environmental Monitoring Systems
Laboratory, Research Triangle Park, NC 27711, 1977.
2. A procedure for Establishing Traceability of Gas Mixtures to
Certain National Bureau of Standards Standard Reference Materials. EPA-
600/7-81-010, U.S. Environmental Protection Agency, Environmental
Monitoring Systems Laboratory (MD-77), Research Triangle Park, NC 27711,
January 1981.
[[Page 39]]
[[Page 40]]
[47 FR 54922, Dec. 6, 1982; 48 FR 17355, Apr. 22, 1983]
[[Page 41]]
Appendix D to Part 50--Measurement Principle and Calibration Procedure
for the Measurement of Ozone in the Atmosphere
Measurement Principle
1. Ambient air and ethylene are delivered simultaneously to a mixing
zone where the ozone in the air reacts with the ethylene to emit light,
which is detected by a photomultiplier tube. The resulting photocurrent
is amplified and is either read directly or displayed on a recorder.
2. An analyzer based on this principle will be considered a
reference method only if it has been designated as a reference method in
accordance with part 53 of this chapter and calibrated as follows:
Calibration Procedure
1. Principle. The calibration procedure is based on the photometric
assay of ozone (O3) concentrations in a dynamic flow system.
The concentration of O3 in an absorption cell is determined
from a measurement of the amount of 254 nm light absorbed by the sample.
This determination requires knowledge of (1) the absorption coefficient
([alpha]) of O3 at 254 nm, (2) the optical path length (l)
through the sample, (3) the transmittance of the sample at a wavelength
of 254 nm, and (4) the temperature (T) and pressure (P) of the sample.
The transmittance is defined as the ratio I/I0, where I is
the intensity of light which passes through the cell and is sensed by
the detector when the cell contains an O3 sample, and
I0 is the intensity of light which passes through the cell
and is sensed by the detector when the cell contains zero air. It is
assumed that all conditions of the system, except for the contents of
the absorption cell, are identical during measurement of I and
I0. The quantities defined above are related by the Beer-
Lambert absorption law,
[GRAPHIC] [TIFF OMITTED] TR31AU93.028
where:
[alpha] = absorption coefficient of O3 at 254 nm=308 4 atm-1 cm-1 at 0 [deg]C and 760
torr.\3\(1, 2, 3, 4, 5, 6, 7)
c = O3 concentration in atmospheres
l = optical path length in cm
In practice, a stable O3 generator is used to produce
O3 concentrations over the required range. Each O3
concentration is determined from the measurement of the transmittance
(I/I0) of the sample at 254 nm with a photometer of path
length l and calculated from the equation,
[GRAPHIC] [TIFF OMITTED] TR31AU93.029
The calculated O3 concentrations must be corrected for
O3 losses which may occur in the photometer and for the
temperature and pressure of the sample.
2. Applicability. This procedure is applicable to the calibration of
ambient air O3 analyzers, either directly or by means of a
transfer standard certified by this procedure. Transfer standards must
meet the requirements and specifications set forth in Reference 8.
3. Apparatus. A complete UV calibration system consists of an ozone
generator, an output port or manifold, a photometer, an appropriate
source of zero air, and other components as necessary. The configuration
must provide a stable ozone concentration at the system output and allow
the photometer to accurately assay the output concentration to the
precision specified for the photometer (3.1). Figure 1 shows a commonly
used configuration and serves to illustrate the calibration procedure
which follows. Other configurations may require appropriate variations
in the procedural steps. All connections between components in the
calibration system downstream of the O3 generator should be
of glass, Teflon, or other relatively inert materials. Additional
information regarding the assembly of a UV photometric calibration
apparatus is given in Reference 9. For certification of transfer
standards which provide their own source of O3, the transfer
standard may replace the O3 generator and possibly other
components shown in Figure 1; see Reference 8 for guidance.
3.1 UV photometer. The photometer consists of a low-pressure mercury
discharge lamp, (optional) collimation optics, an absorption cell, a
detector, and signal-processing electronics, as illustrated in Figure 1.
It must be capable of measuring the transmittance, I/I0, at a
wavelength of 254 nm with sufficient precision such that the standard
deviation of the concentration measurements does not exceed the greater
of 0.005 ppm or 3% of the concentration. Because the low-pressure
mercury lamp radiates at several wavelengths, the photometer must
incorporate suitable means to assure that no O3 is generated
in the cell by the lamp, and that at least 99.5% of the radiation sensed
by the detector is 254 nm radiation. (This can be readily achieved by
prudent selection of optical filter and detector response
characteristics.) The length of the light path through the absorption
cell must be known with an accuracy of at least 99.5%. In addition, the
cell and associated plumbing must be designed to
[[Page 42]]
minimize loss of O3 from contact with cell walls and gas
handling components. See Reference 9 for additional information.
3.2 Air flow controllers. Devices capable of regulating air flows as
necessary to meet the output stability and photometer precision
requirements.
3.3 Ozone generator. Device capable of generating stable levels of
O3 over the required concentration range.
3.4 Output manifold. The output manifold should be constructed of
glass, Teflon, or other relatively inert material, and should be of
sufficient diameter to insure a negligible pressure drop at the
photometer connection and other output ports. The system must have a
vent designed to insure atmospheric pressure in the manifold and to
prevent ambient air from entering the manifold.
3.5 Two-way valve. Manual or automatic valve, or other means to
switch the photometer flow between zero air and the O3
concentration.
3.6 Temperature indicator. Accurate to 1
[deg]C.
3.7 Barometer or pressure indicator. Accurate to 2 torr.
4. Reagents.
4.1 Zero air. The zero air must be free of contaminants which would
cause a detectable response from the O3 analyzer, and it
should be free of NO, C2 H4, and other species
which react with O3. A procedure for generating suitable zero
air is given in Reference 9. As shown in Figure 1, the zero air supplied
to the photometer cell for the I0 reference measurement must
be derived from the same source as the zero air used for generation of
the ozone concentration to be assayed (I measurement). When using the
photometer to certify a transfer standard having its own source of
ozone, see Reference 8 for guidance on meeting this requirement.
5. Procedure.
5.1 General operation. The calibration photometer must be dedicated
exclusively to use as a calibration standard. It should always be used
with clean, filtered calibration gases, and never used for ambient air
sampling. Consideration should be given to locating the calibration
photometer in a clean laboratory where it can be stationary, protected
from physical shock, operated by a responsible analyst, and used as a
common standard for all field calibrations via transfer standards.
5.2 Preparation. Proper operation of the photometer is of critical
importance to the accuracy of this procedure. The following steps will
help to verify proper operation. The steps are not necessarily required
prior to each use of the photometer. Upon initial operation of the
photometer, these steps should be carried out frequently, with all
quantitative results or indications recorded in a chronological record
either in tabular form or plotted on a graphical chart. As the
performance and stability record of the photometer is established, the
frequency of these steps may be reduced consistent with the documented
stability of the photometer.
5.2.1 Instruction manual: Carry out all set up and adjustment
procedures or checks as described in the operation or instruction manual
associated with the photometer.
5.2.2 System check: Check the photometer system for integrity,
leaks, cleanliness, proper flowrates, etc. Service or replace filters
and zero air scrubbers or other consumable materials, as necessary.
5.2.3 Linearity: Verify that the photometer manufacturer has
adequately established that the linearity error of the photometer is
less than 3%, or test the linearity by dilution as follows: Generate and
assay an O3 concentration near the upper range limit of the
system (0.5 or 1.0 ppm), then accurately dilute that concentration with
zero air and reassay it. Repeat at several different dilution ratios.
Compare the assay of the original concentration with the assay of the
diluted concentration divided by the dilution ratio, as follows
[GRAPHIC] [TIFF OMITTED] TR31AU93.030
where:
E = linearity error, percent
A1 = assay of the original concentration
A2 = assay of the diluted concentration
R = dilution ratio = flow of original concentration divided by the total
flow
The linearity error must be less than 5%. Since the accuracy of the
measured flow-rates will affect the linearity error as measured this
way, the test is not necessarily conclusive. Additional information on
verifying linearity is contained in Reference 9.
5.2.4 Intercomparison: When possible, the photometer should be
occasionally intercompared, either directly or via transfer standards,
with calibration photometers used by other agencies or laboratories.
5.2.5 Ozone losses: Some portion of the O3 may be lost
upon contact with the photometer cell walls and gas handling components.
The magnitude of this loss must be determined and used to correct the
calculated O3 concentration. This loss must not exceed 5%.
Some guidelines for quantitatively determining this loss are discussed
in Reference 9.
5.3 Assay of O3 concentrations.
5.3.1 Allow the photometer system to warm up and stabilizer.
5.3.2 Verify that the flowrate through the photometer absorption
cell, F allows the cell to be flushed in a reasonably short period of
time (2 liter/min is a typical flow). The precision of the measurements
is inversely related to the time required for flushing, since the
photometer drift error increases with time.
[[Page 43]]
5.3.3 Insure that the flowrate into the output manifold is at least
1 liter/min greater than the total flowrate required by the photometer
and any other flow demand connected to the manifold.
5.3.4 Insure that the flowrate of zero air, Fz, is at
least 1 liter/min greater than the flowrate required by the photometer.
5.3.5 With zero air flowing in the output manifold, actuate the two-
way valve to allow the photometer to sample first the manifold zero air,
then Fz. The two photometer readings must be equal
(I=Io).
Note: In some commercially available photometers, the operation of
the two-way valve and various other operations in section 5.3 may be
carried out automatically by the photometer.
5.3.6 Adjust the O3 generator to produce an O3
concentration as needed.
5.3.7 Actuate the two-way valve to allow the photometer to sample
zero air until the absorption cell is thoroughly flushed and record the
stable measured value of Io.
5.3.8 Actuate the two-way valve to allow the photometer to sample
the ozone concentration until the absorption cell is thoroughly flushed
and record the stable measured value of I.
5.3.9 Record the temperature and pressure of the sample in the
photometer absorption cell. (See Reference 9 for guidance.)
5.3.10 Calculate the O3 concentration from equation 4. An
average of several determinations will provide better precision.
[GRAPHIC] [TIFF OMITTED] TR31AU93.032
where:
[O3]OUT = O3 concentration, ppm
[alpha] = absorption coefficient of O3 at 254 nm=308
atm-1 cm-1 at 0 [deg]C and 760 torr
l = optical path length, cm
T = sample temperature, K
P = sample pressure, torr
L = correction factor for O3 losses from 5.2.5=(1-fraction
O3 lost).
Note: Some commercial photometers may automatically evaluate all or
part of equation 4. It is the operator's responsibility to verify that
all of the information required for equation 4 is obtained, either
automatically by the photometer or manually. For ``automatic''
photometers which evaluate the first term of equation 4 based on a
linear approximation, a manual correction may be required, particularly
at higher O3 levels. See the photometer instruction manual
and Reference 9 for guidance.
5.3.11 Obtain additional O3 concentration standards as
necessary by repeating steps 5.3.6 to 5.3.10 or by Option 1.
5.4 Certification of transfer standards. A transfer standard is
certified by relating the output of the transfer standard to one or more
ozone standards as determined according to section 5.3. The exact
procedure varies depending on the nature and design of the transfer
standard. Consult Reference 8 for guidance.
5.5 Calibration of ozone analyzers. Ozone analyzers are calibrated
as follows, using ozone standards obtained directly according to section
5.3 or by means of a certified transfer standard.
5.5.1 Allow sufficient time for the O3 analyzer and the
photometer or transfer standard to warmup and stabilize.
5.5.2 Allow the O3 analyzer to sample zero air until a
stable response is obtained and adjust the O3 analyzer's zero
control. Offsetting the analyzer's zero adjustment to +5% of scale is
recommended to facilitate observing negative zero drift. Record the
stable zero air response as ``Z''.
5.5.3 Generate an O3 concentration standard of
approximately 80% of the desired upper range limit (URL) of the
O3 analyzer. Allow the O3 analyzer to sample this
O3 concentration standard until a stable response is
obtained.
5.5.4 Adjust the O3 analyzer's span control to obtain a
convenient recorder response as indicated below:
recorder response (%scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.033
where:
URL = upper range limit of the O3 analyzer, ppm
Z = recorder response with zero air, % scale
Record the O3 concentration and the corresponding
analyzer response. If substantial adjustment of the span control is
necessary, recheck the zero and span adjustments by repeating steps
5.5.2 to 5.5.4.
5.5.5 Generate several other O3 concentration standards
(at least 5 others are recommended) over the scale range of the
O3 analyzer by adjusting the O3 source or by
Option 1. For each O3 concentration standard, record the
O3 and the corresponding analyzer response.
5.5.6 Plot the O3 analyzer responses versus the
corresponding O3 concentrations and draw the O3
analyzer's calibration curve or calculate the appropriate response
factor.
5.5.7 Option 1: The various O3 concentrations required in
steps 5.3.11 and 5.5.5 may be obtained by dilution of the O3
concentration generated in steps 5.3.6 and 5.5.3. With this option,
accurate flow measurements are required. The dynamic calibration system
may be modified as shown in Figure 2 to allow for dilution air to be
metered in downstream of the O3 generator. A mixing chamber
between the O3 generator and the output manifold is also
required. The flowrate through the O3 generator
(Fo) and the dilution air flowrate
[[Page 44]]
(FD) are measured with a reliable flow or volume standard
traceable to NBS. Each O3 concentration generated by dilution
is calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.031
where:
[O3]'OUT = diluted O3 concentration,
ppm
F0 = flowrate through the O3 generator, liter/min
FD = diluent air flowrate, liter/min
References
1. E.C.Y. Inn and Y. Tanaka, ``Absorption coefficient of Ozone in
the Ultraviolet and Visible Regions'', J. Opt. Soc. Am., 43, 870 (1953).
2. A. G. Hearn, ``Absorption of Ozone in the Ultraviolet and Visible
Regions of the Spectrum'', Proc. Phys. Soc. (London), 78, 932 (1961).
3. W. B. DeMore and O. Raper, ``Hartley Band Extinction Coefficients
of Ozone in the Gas Phase and in Liquid Nitrogen, Carbon Monoxide, and
Argon'', J. Phys. Chem., 68, 412 (1964).
4. M. Griggs, ``Absorption Coefficients of Ozone in the Ultraviolet
and Visible Regions'', J. Chem. Phys., 49, 857 (1968).
5. K. H. Becker, U. Schurath, and H. Seitz, ``Ozone Olefin Reactions
in the Gas Phase. 1. Rate Constants and Activation Energies'', Int'l
Jour. of Chem. Kinetics, VI, 725 (1974).
6. M. A. A. Clyne and J. A. Coxom, ``Kinetic Studies of Oxy-halogen
Radical Systems'', Proc. Roy. Soc., A303, 207 (1968).
7. J. W. Simons, R. J. Paur, H. A. Webster, and E. J. Bair, ``Ozone
Ultraviolet Photolysis. VI. The Ultraviolet Spectrum'', J. Chem. Phys.,
59, 1203 (1973).
8. Transfer Standards for Calibration of Ambient Air Monitoring
Analyzers for Ozone, EPA publication number EPA-600/4-79-056, EPA,
National Exposure Research Laboratory, Department E, (MD-77B), Research
Triangle Park, NC 27711.
9. Technical Assistance Document for the Calibration of Ambient
Ozone Monitors, EPA publication number EPA-600/4-79-057, EPA, National
Exposure Research Laboratory, Department E, (MD-77B), Research Triangle
Park, NC 27711.
[[Page 45]]
[44 FR 8224, Feb. 8, 1979, as amended at 62 FR 38895, July 18, 1997]
[[Page 46]]
Appendix E to Part 50 [Reserved]
Appendix F to Part 50--Measurement Principle and Calibration Procedure
for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase
Chemiluminescence)
Principle and Applicability
1. Atmospheric concentrations of nitrogen dioxide (NO2)
are measured indirectly by photometrically measuring the light
intensity, at wavelengths greater than 600 nanometers, resulting from
the chemiluminescent reaction of nitric oxide (NO) with ozone
(O3). (1,2,3) NO2 is first quantitatively reduced
to NO(4,5,6) by means of a converter. NO, which commonly exists in
ambient air together with NO2, passes through the converter
unchanged causing a resultant total NOX concentration equal
to NO+NO2. A sample of the input air is also measured without
having passed through the converted. This latter NO measurement is
subtracted from the former measurement (NO+NO2) to yield the
final NO2 measurement. The NO and NO+NO2
measurements may be made concurrently with dual systems, or cyclically
with the same system provided the cycle time does not exceed 1 minute.
2. Sampling considerations.
2.1 Chemiluminescence NO/NOX/NO2 analyzers
will respond to other nitrogen containing compounds, such as
peroxyacetyl nitrate (PAN), which might be reduced to NO in the thermal
converter. (7) Atmospheric concentrations of these potential
interferences are generally low relative to NO2 and valid
NO2 measurements may be obtained. In certain geographical
areas, where the concentration of these potential interferences is known
or suspected to be high relative to NO2, the use of an
equivalent method for the measurement of NO2 is recommended.
2.2 The use of integrating flasks on the sample inlet line of
chemiluminescence NO/NOX/NO2 analyzers is optional
and left to couraged. The sample residence time between the sampling
point and the analyzer should be kept to a minimum to avoid erroneous
NO2 measurements resulting from the reaction of ambient
levels of NO and O3 in the sampling system.
2.3 The use of particulate filters on the sample inlet line of
chemiluminescence NO/NOX/NO2 analyzers is optional
and left to the discretion of the user or the manufacturer.
Use of the filter should depend on the analyzer's susceptibility to
interference, malfunction, or damage due to particulates. Users are
cautioned that particulate matter concentrated on a filter may cause
erroneous NO2 measurements and therefore filters should be
changed frequently.
3. An analyzer based on this principle will be considered a
reference method only if it has been designated as a reference method in
accordance with part 53 of this chapter.
Calibration
1. Alternative A--Gas phase titration (GPT) of an NO standard with
O3.
Major equipment required: Stable O3 generator.
Chemiluminescence NO/NOX/NO2 analyzer with strip
chart recorder(s). NO concentration standard.
1.1 Principle. This calibration technique is based upon the rapid
gas phase reaction between NO and O3 to produce
stoichiometric quantities of NO2 in accordance with the
following equation: (8)
[GRAPHIC] [TIFF OMITTED] TC08NO91.075
The quantitative nature of this reaction is such that when the NO
concentration is known, the concentration of NO2 can be
determined. Ozone is added to excess NO in a dynamic calibration system,
and the NO channel of the chemiluminescence NO/NOX/
NO2 analyzer is used as an indicator of changes in NO
concentration. Upon the addition of O3, the decrease in NO
concentration observed on the calibrated NO channel is equivalent to the
concentration of NO2 produced. The amount of NO2
generated may be varied by adding variable amounts of O3 from
a stable uncalibrated O3 generator. (9)
1.2 Apparatus. Figure 1, a schematic of a typical GPT apparatus,
shows the suggested configuration of the components listed below. All
connections between components in the calibration system downstream from
the O3 generator should be of glass, Teflon[reg],
or other non-reactive material.
1.2.1 Air flow controllers. Devices capable of maintaining constant
air flows within 2% of the required flowrate.
1.2.2 NO flow controller. A device capable of maintaining constant
NO flows within 2% of the required flowrate.
Component parts in contact with the NO should be of a non-reactive
material.
1.2.3 Air flowmeters. Calibrated flowmeters capable of measuring and
monitoring air flowrates with an accuracy of 2% of
the measured flowrate.
1.2.4 NO flowmeter. A calibrated flowmeter capable of measuring and
monitoring NO flowrates with an accuracy of 2% of
the measured flowrate. (Rotameters have been reported to operate
unreliably when measuring low NO flows and are not recommended.)
1.2.5 Pressure regulator for standard NO cylinder. This regulator
must have a nonreactive diaphragm and internal parts and a suitable
delivery pressure.
1.2.6 Ozone generator. The generator must be capable of generating
sufficient and stable levels of O3 for reaction with NO to
generate
[[Page 47]]
NO2 concentrations in the range required. Ozone generators of
the electric discharge type may produce NO and NO2 and are
not recommended.
1.2.7 Valve. A valve may be used as shown in Figure 1 to divert the
NO flow when zero air is required at the manifold. The valve should be
constructed of glass, Teflon[reg], or other nonreactive
material.
1.2.8 Reaction chamber. A chamber, constructed of glass,
Teflon[reg], or other nonreactive material, for the
quantitative reaction of O3 with excess NO. The chamber
should be of sufficient volume (VRC) such that the residence time
(tR) meets the requirements specified in 1.4. For practical
reasons, tR should be less than 2 minutes.
1.2.9 Mixing chamber. A chamber constructed of glass,
Teflon[reg], or other nonreactive material and designed to
provide thorough mixing of reaction products and diluent air. The
residence time is not critical when the dynamic parameter specification
given in 1.4 is met.
1.2.10 Output manifold. The output manifold should be constructed of
glass, Teflon[reg], or other non-reactive material and should
be of sufficient diameter to insure an insignificant pressure drop at
the analyzer connection. The system must have a vent designed to insure
atmospheric pressure at the manifold and to prevent ambient air from
entering the manifold.
1.3 Reagents.
1.3.1 NO concentration standard. Gas cylinder standard containing 50
to 100 ppm NO in N2 with less than 1 ppm NO2. This
standard must be traceable to a National Bureau of Standards (NBS) NO in
N2 Standard Reference Material (SRM 1683 or SRM 1684), an NBS
NO2 Standard Reference Material (SRM 1629), or an NBS/EPA-
approved commercially available Certified Reference Material (CRM).
CRM's are described in Reference 14, and a list of CRM sources is
available from the address shown for Reference 14. A recommended
protocol for certifying NO gas cylinders against either an NO SRM or CRM
is given in section 2.0.7 of Reference 15. Reference 13 gives procedures
for certifying an NO gas cylinder against an NBS NO2 SRM and
for determining the amount of NO2 impurity in an NO cylinder.
1.3.2 Zero air. Air, free of contaminants which will cause a
detectable response on the NO/NOX/NO2 analyzer or
which might react with either NO, O3, or NO2 in
the gas phase titration. A procedure for generating zero air is given in
reference 13.
1.4 Dynamic parameter specification.
1.4.1 The O3 generator air flowrate (F0) and
NO flowrate (FNO) (see Figure 1) must be adjusted such that
the following relationship holds:
[GRAPHIC] [TIFF OMITTED] TC08NO91.076
[GRAPHIC] [TIFF OMITTED] TC08NO91.077
[GRAPHIC] [TIFF OMITTED] TC08NO91.078
where:
PR = dynamic parameter specification, determined empirically, to insure
complete reaction of the available O3, ppm-minute
[NO]RC = NO concentration in the reaction chamber, ppm
R = residence time of the reactant gases in the reaction chamber, minute
[NO]STD = concentration of the undiluted NO standard, ppm
FNO = NO flowrate, scm\3\/min
FO = O3 generator air flowrate, scm\3\/min
VRC = volume of the reaction chamber, scm\3\
1.4.2 The flow conditions to be used in the GPT system are
determined by the following procedure:
(a) Determine FT, the total flow required at the output manifold
(FT=analyzer demand plus 10 to 50% excess).
(b) Establish [NO]OUT as the highest NO concentration
(ppm) which will be required at the output manifold. [NO]OUT
should be approximately equivalent to 90% of the upper range limit (URL)
of the NO2 concentration range to be covered.
(c) Determine FNO as
[GRAPHIC] [TIFF OMITTED] TC08NO91.079
(d) Select a convenient or available reaction chamber volume.
Initially, a trial VRC may be selected to be in the range of
approximately 200 to 500 scm\3\.
(e) Compute FO as
(f) Compute tR as
[GRAPHIC] [TIFF OMITTED] TC08NO91.080
Verify that tR < 2 minutes. If not, select a reaction chamber with a
smaller VRC.
(g) Compute the diluent air flowrate as
[GRAPHIC] [TIFF OMITTED] TC08NO91.081
where:
FD = diluent air flowrate, scm\3\/min
(h) If FO turns out to be impractical for the desired system, select
a reaction chamber
[[Page 48]]
having a different VRC and recompute FO and FD.
Note: A dynamic parameter lower than 2.75 ppm-minutes may be used if
it can be determined empirically that quantitative reaction of
O3 with NO occurs. A procedure for making this determination
as well as a more detailed discussion of the above requirements and
other related considerations is given in reference 13.
1.5 Procedure.
1.5.1 Assemble a dynamic calibration system such as the one shown in
Figure 1.
1.5.2 Insure that all flowmeters are calibrated under the conditions
of use against a reliable standard such as a soap-bubble meter or wet-
test meter. All volumetric flowrates should be corrected to 25 [deg]C
and 760 mm Hg. A discussion on the calibration of flowmeters is given in
reference 13.
1.5.3 Precautions must be taken to remove O2 and other
contaminants from the NO pressure regulator and delivery system prior to
the start of calibration to avoid any conversion of the standard NO to
NO2. Failure to do so can cause significant errors in
calibration. This problem may be minimized by (1) carefully evacuating
the regulator, when possible, after the regulator has been connected to
the cylinder and before opening the cylinder valve; (2) thoroughly
flushing the regulator and delivery system with NO after opening the
cylinder valve; (3) not removing the regulator from the cylinder between
calibrations unless absolutely necessary. Further discussion of these
procedures is given in reference 13.
1.5.4 Select the operating range of the NO/NOX/
NO2 analyzer to be calibrated. In order to obtain maximum
precision and accuracy for NO2 calibration, all three
channels of the analyzer should be set to the same range. If operation
of the NO and NOX channels on higher ranges is desired,
subsequent recalibration of the NO and NOX channels on the
higher ranges is recommended.
Note: Some analyzer designs may require identical ranges for NO,
NOX, and NO2 during operation of the analyzer.
1.5.5 Connect the recorder output cable(s) of the NO/NOX/
NO2 analyzer to the input terminals of the strip chart
recorder(s). All adjustments to the analyzer should be performed based
on the appropriate strip chart readings. References to analyzer
responses in the procedures given below refer to recorder responses.
1.5.6 Determine the GPT flow conditions required to meet the dynamic
parameter specification as indicated in 1.4.
1.5.7 Adjust the diluent air and O3 generator air flows
to obtain the flows determined in section 1.4.2. The total air flow must
exceed the total demand of the analyzer(s) connected to the output
manifold to insure that no ambient air is pulled into the manifold vent.
Allow the analyzer to sample zero air until stable NO, NOX,
and NO2 responses are obtained. After the responses have
stabilized, adjust the analyzer zero control(s).
Note: Some analyzers may have separate zero controls for NO,
NOX, and NO2. Other analyzers may have separate
zero controls only for NO and NOX, while still others may
have only one zero control common to all three channels.
Offsetting the analyzer zero adjustments to +5 percent of scale is
recommended to facilitate observing negative zero drift. Record the
stable zero air responses as ZNO, Znox, and Zno2.
1.5.8 Preparation of NO and NOX calibration curves.
1.5.8.1 Adjustment of NO span control. Adjust the NO flow from the
standard NO cylinder to generate an NO concentration of approximately 80
percent of the upper range limit (URL) of the NO range. This exact NO
concentration is calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.044
where:
[NO]OUT = diluted NO concentration at the output manifold, ppm
Sample this NO concentration until the NO and NOX responses
have stabilized. Adjust the NO span control to obtain a recorder
response as indicated below:
recorder response (percent scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.045
where:
URL = nominal upper range limit of the NO channel, ppm
Note: Some analyzers may have separate span controls for NO,
NOX, and NO2. Other analyzers may have separate
span controls only for NO and NOX, while still others may
have only one span control common to all three channels. When only one
span control is available, the span adjustment is made on the NO channel
of the analyzer.
If substantial adjustment of the NO span control is necessary, it may be
necessary to recheck the zero and span adjustments by repeating steps
1.5.7 and 1.5.8.1. Record the NO concentration and the analyzer's NO
response.
1.5.8.2 Adjustment of NOX span control. When adjusting
the analyzer's NOX span control, the presence of any
NO2 impurity in the standard NO cylinder must be taken into
account. Procedures for determining the amount of NO2
impurity in the standard NO cylinder are given in reference 13. The
exact NOX concentration is calculated from:
[[Page 49]]
[GRAPHIC] [TIFF OMITTED] TR31AU93.046
where:
[NOX]OUT = diluted NOX concentration at
the output manifold, ppm
[NO2]IMP = concentration of NO2
impurity in the standard NO cylinder, ppm
Adjust the NOX span control to obtain a recorder response as
indicated below:
recorder response (% scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.047
Note: If the analyzer has only one span control, the span adjustment
is made on the NO channel and no further adjustment is made here for
NOX.
If substantial adjustment of the NOX span control is
necessary, it may be necessary to recheck the zero and span adjustments
by repeating steps 1.5.7 and 1.5.8.2. Record the NOX
concentration and the analyzer's NOX response.
1.5.8.3 Generate several additional concentrations (at least five
evenly spaced points across the remaining scale are suggested to verify
linearity) by decreasing FNO or increasing FD. For
each concentration generated, calculate the exact NO and NOX
concentrations using equations (9) and (11) respectively. Record the
analyzer's NO and NOX responses for each concentration. Plot
the analyzer responses versus the respective calculated NO and
NOX concentrations and draw or calculate the NO and
NOX calibration curves. For subsequent calibrations where
linearity can be assumed, these curves may be checked with a two-point
calibration consisting of a zero air point and NO and NOX
concentrations of approximately 80% of the URL.
1.5.9 Preparation of NO2 calibration curve.
1.5.9.1 Assuming the NO2 zero has been properly adjusted
while sampling zero air in step 1.5.7, adjust FO and
FD as determined in section 1.4.2. Adjust FNO to
generate an NO concentration near 90% of the URL of the NO range. Sample
this NO concentration until the NO and NOX responses have
stabilized. Using the NO calibration curve obtained in section 1.5.8,
measure and record the NO concentration as [NO]orig. Using
the NOX calibration curve obtained in section 1.5.8, measure
and record the NOX concentration as
[NOX]orig.
1.5.9.2 Adjust the O3 generator to generate sufficient
O3 to produce a decrease in the NO concentration equivalent
to approximately 80% of the URL of the NO2 range. The
decrease must not exceed 90% of the NO concentration determined in step
1.5.9.1. After the analyzer responses have stabilized, record the
resultant NO and NOX concentrations as [NO]rem and
[NOX]rem.
1.5.9.3 Calculate the resulting NO2 concentration from:
[GRAPHIC] [TIFF OMITTED] TC08NO91.082
where:
[NO2]OUT = diluted NO2 concentration at
the output manifold, ppm
[NO]orig = original NO concentration, prior to addition of
O3, ppm
[NO]rem = NO concentration remaining after addition of
O3, ppm
Adjust the NO2 span control to obtain a recorder response as
indicated below:
recorder response (% scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.048
Note: If the analyzer has only one or two span controls, the span
adjustments are made on the NO channel or NO and NOX channels
and no further adjustment is made here for NO2.
If substantial adjustment of the NO2 span control is
necessary, it may be necessary to recheck the zero and span adjustments
by repeating steps 1.5.7 and 1.5.9.3. Record the NO2
concentration and the corresponding analyzer NO2 and
NOX responses.
1.5.9.4 Maintaining the same FNO, FO, and
FD as in section 1.5.9.1, adjust the ozone generator to
obtain several other concentrations of NO2 over the
NO2 range (at least five evenly spaced points across the
remaining scale are suggested). Calculate each NO2
concentration using equation (13) and record the corresponding analyzer
NO2 and NOX responses. Plot the analyzer's
NO2 responses versus the corresponding calculated
NO2 concentrations and draw or calculate the NO2
calibration curve.
1.5.10 Determination of converter efficiency.
1.5.10.1 For each NO2 concentration generated during the
preparation of the NO2 calibration curve (see section 1.5.9)
calculate the concentration of NO2 converted from:
[[Page 50]]
[GRAPHIC] [TIFF OMITTED] TC08NO91.083
where:
[NO2]CONV = concentration of NO2
converted, ppm
[NOX]orig = original NOX concentration
prior to addition of O3, ppm
[NOX]rem = NOX concentration remaining
after addition of O3, ppm
Note: Supplemental information on calibration and other procedures
in this method are given in reference 13.
Plot [NO2]CONV (y-axis) versus
[NO2]OUT (x-axis) and draw or calculate the
converter efficiency curve. The slope of the curve times 100 is the
average converter efficiency, EC The average converter
efficiency must be greater than 96%; if it is less than 96%, replace or
service the converter.
2. Alternative B--NO2 permeation device.
Major equipment required:
Stable O3 generator.
Chemiluminescence NO/NOX/NO2 analyzer with strip chart
recorder(s).
NO concentration standard.
NO2 concentration standard.
2.1 Principle. Atmospheres containing accurately known
concentrations of nitrogen dioxide are generated by means of a
permeation device. (10) The permeation device emits NO2 at a
known constant rate provided the temperature of the device is held
constant (0.1 [deg]C) and the device has been
accurately calibrated at the temperature of use. The NO2
emitted from the device is diluted with zero air to produce
NO2 concentrations suitable for calibration of the
NO2 channel of the NO/NOX/NO2 analyzer. An NO
concentration standard is used for calibration of the NO and NOX
channels of the analyzer.
2.2 Apparatus. A typical system suitable for generating the required
NO and NO2 concentrations is shown in Figure 2. All
connections between components downstream from the permeation device
should be of glass, Teflon[reg], or other non-reactive
material.
2.2.1 Air flow controllers. Devices capable of maintaining constant
air flows within 2% of the required flowrate.
2.2.2 NO flow controller. A device capable of maintaining constant
NO flows within 2% of the required flowrate.
Component parts in contact with the NO must be of a non-reactive
material.
2.2.3 Air flowmeters. Calibrated flowmeters capable of measuring and
monitoring air flowrates with an accuracy of 2% of
the measured flowrate.
2.2.4 NO flowmeter. A calibrated flowmeter capable of measuring and
monitoring NO flowrates with an accuracy of 2% of
the measured flowrate. (Rotameters have been reported to operate
unreliably when measuring low NO flows and are not recommended.)
2.2.5 Pressure regulator for standard NO cylinder. This regulator
must have a non-reactive diaphragm and internal parts and a suitable
delivery pressure.
2.2.6 Drier. Scrubber to remove moisture from the permeation device
air system. The use of the drier is optional with NO2
permeation devices not sensitive to moisture. (Refer to the supplier's
instructions for use of the permeation device.)
2.2.7 Constant temperature chamber. Chamber capable of housing the
NO2 permeation device and maintaining its temperature to
within 0.1 [deg]C.
2.2.8 Temperature measuring device. Device capable of measuring and
monitoring the temperature of the NO2 permeation device with
an accuracy of 0.05 [deg]C.
2.2.9 Valves. A valve may be used as shown in Figure 2 to divert the
NO2 from the permeation device when zero air or NO is
required at the manifold. A second valve may be used to divert the NO
flow when zero air or NO2 is required at the manifold.
The valves should be constructed of glass, Teflon[reg],
or other nonreactive material.
2.2.10 Mixing chamber. A chamber constructed of glass,
Teflon[reg], or other nonreactive material and designed to
provide thorough mixing of pollutant gas streams and diluent air.
2.2.11 Output manifold. The output manifold should be constructed of
glass, Teflon[reg], or other non-reactive material and should
be of sufficient diameter to insure an insignificant pressure drop at
the analyzer connection. The system must have a vent designed to insure
atmospheric pressure at the manifold and to prevent ambient air from
entering the manifold.
2.3 Reagents.
2.3.1 Calibration standards. Calibration standards are required for
both NO and NO2. The reference standard for the calibration
may be either an NO or NO2 standard, and must be traceable to
a National Bureau of Standards (NBS) NO in N2 Standard
Reference Material (SRM 1683 or SRM 1684), and NBS NO2
Standard Reference Material (SRM 1629), or an NBS/EPA-approved
commercially available Certified Reference Material (CRM). CRM's are
described in Reference 14, and a list of CRM sources is available from
the address shown for Reference 14. Reference 15 gives recommended
procedures for certifying an NO gas cylinder against an NO
[[Page 51]]
SRM or CRM and for certifying an NO2 permeation device
against an NO2 SRM. Reference 13 contains procedures for
certifying an NO gas cylinder against an NO2 SRM and for
certifying an NO2 permeation device against an NO SRM or CRM.
A procedure for determining the amount of NO2 impurity in an
NO cylinder is also contained in Reference 13. The NO or NO2
standard selected as the reference standard must be used to certify the
other standard to ensure consistency between the two standards.
2.3.1.1 NO2 Concentration standard. A permeation device
suitable for generating NO2 concentrations at the required
flow-rates over the required concentration range. If the permeation
device is used as the reference standard, it must be traceable to an SRM
or CRM as specified in 2.3.1. If an NO cylinder is used as the reference
standard, the NO2 permeation device must be certified against
the NO standard according to the procedure given in Reference 13. The
use of the permeation device should be in strict accordance with the
instructions supplied with the device. Additional information regarding
the use of permeation devices is given by Scaringelli et al. (11) and
Rook et al. (12).
2.3.1.2 NO Concentration standard. Gas cylinder containing 50 to 100
ppm NO in N2 with less than 1 ppm NO2. If this
cylinder is used as the reference standard, the cylinder must be
traceable to an SRM or CRM as specified in 2.3.1. If an NO2
permeation device is used as the reference standard, the NO cylinder
must be certified against the NO2 standard according to the
procedure given in Reference 13. The cylinder should be recertified on a
regular basis as determined by the local quality control program.
2.3.3 Zero air. Air, free of contaminants which might react with NO
or NO2 or cause a detectable response on the NO/NOX/
NO2 analyzer. When using permeation devices that are
sensitive to moisture, the zero air passing across the permeation device
must be dry to avoid surface reactions on the device. (Refer to the
supplier's instructions for use of the permeation device.) A procedure
for generating zero air is given in reference 13.
2.4 Procedure.
2.4.1 Assemble the calibration apparatus such as the typical one
shown in Figure 2.
2.4.2 Insure that all flowmeters are calibrated under the conditions
of use against a reliable standard such as a soap bubble meter or wet-
test meter. All volumetric flowrates should be corrected to 25 [deg]C
and 760 mm Hg. A discussion on the calibration of flowmeters is given in
reference 13.
2.4.3 Install the permeation device in the constant temperature
chamber. Provide a small fixed air flow (200-400 scm\3\/min) across the
device. The permeation device should always have a continuous air flow
across it to prevent large buildup of NO2 in the system and a
consequent restabilization period. Record the flowrate as FP. Allow the
device to stabilize at the calibration temperature for at least 24
hours. The temperature must be adjusted and controlled to within 0.1 [deg]C or less of the calibration temperature as
monitored with the temperature measuring device.
2.4.4 Precautions must be taken to remove O2 and other
contaminants from the NO pressure regulator and delivery system prior to
the start of calibration to avoid any conversion of the standard NO to
NO2. Failure to do so can cause significant errors in
calibration. This problem may be minimized by
(1) Carefully evacuating the regulator, when possible, after the
regulator has been connected to the cylinder and before opening the
cylinder valve;
(2) Thoroughly flushing the regulator and delivery system with NO
after opening the cylinder valve;
(3) Not removing the regulator from the cylinder between
calibrations unless absolutely necessary. Further discussion of these
procedures is given in reference 13.
2.4.5 Select the operating range of the NO/NOX NO2
analyzer to be calibrated. In order to obtain maximum precision and
accuracy for NO2 calibration, all three channels of the
analyzer should be set to the same range. If operation of the NO and NOX
channels on higher ranges is desired, subsequent recalibration of the NO
and NOX channels on the higher ranges is recommended.
Note: Some analyzer designs may require identical ranges for NO,
NOX, and NO2 during operation of the analyzer.
2.4.6 Connect the recorder output cable(s) of the NO/NOX/
NO2 analyzer to the input terminals of the strip chart
recorder(s). All adjustments to the analyzer should be performed based
on the appropriate strip chart readings. References to analyzer
responses in the procedures given below refer to recorder responses.
2.4.7 Switch the valve to vent the flow from the permeation device
and adjust the diluent air flowrate, FD, to provide zero air at the
output manifold. The total air flow must exceed the total demand of the
analyzer(s) connected to the output manifold to insure that no ambient
air is pulled into the manifold vent. Allow the analyzer to sample zero
air until stable NO, NOX, and NO2 responses are obtained.
After the responses have stabilized, adjust the analyzer zero
control(s).
Note: Some analyzers may have separate zero controls for NO, NOX,
and NO2. Other analyzers may have separate zero controls only
for NO and NOX, while still others may have only one zero common control
to all three channels.
Offsetting the analyzer zero adjustments to +5% of scale is recommended
to facilitate observing negative zero drift. Record the stable zero air
responses as ZNO, ZNOX, and
ZNO2.
[[Page 52]]
2.4.8 Preparation of NO and NOX calibration curves.
2.4.8.1 Adjustment of NO span control. Adjust the NO flow from the
standard NO cylinder to generate an NO concentration of approximately
80% of the upper range limit (URL) of the NO range. The exact NO
concentration is calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.049
where:
[NO]OUT = diluted NO concentration at the output manifold,
ppm
FNO = NO flowrate, scm\3\/min
[NO]STD=concentration of the undiluted NO standard, ppm
FD = diluent air flowrate, scm\3\/min
Sample this NO concentration until the NO and NOX responses have
stabilized. Adjust the NO span control to obtain a recorder response as
indicated below:
recorder response (% scale) =
[GRAPHIC] [TIFF OMITTED] TR31AU93.050
[GRAPHIC] [TIFF OMITTED] TR31AU93.051
where:
URL = nominal upper range limit of the NO channel, ppm
Note: Some analyzers may have separate span controls for NO, NOX,
and NO2. Other analyzers may have separate span controls only
for NO and NOX, while still others may have only one span control common
to all three channels. When only one span control is available, the span
adjustment is made on the NO channel of the analyzer.
If substantial adjustment of the NO span control is necessary, it may be
necessary to recheck the zero and span adjustments by repeating steps
2.4.7 and 2.4.8.1. Record the NO concentration and the analyzer's NO
response.
2.4.8.2 Adjustment of NOX span control. When adjusting the
analyzer's NOX span control, the presence of any NO2 impurity
in the standard NO cylinder must be taken into account. Procedures for
determining the amount of NO2 impurity in the standard NO
cylinder are given in reference 13. The exact NOX concentration is
calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.052
where:
[NOX]OUT = diluted NOX cencentration at
the output manifold, ppm
[NO2]IMP = concentration of NO2
impurity in the standard NO cylinder, ppm
Adjust the NOX span control to obtain a convenient recorder response as
indicated below:
recorder response (% scale)
[GRAPHIC] [TIFF OMITTED] TR31AU93.053
Note: If the analyzer has only one span control, the span adjustment
is made on the NO channel and no further adjustment is made here for
NOX.
If substantial adjustment of the NOX span control is
necessary, it may be necessary to recheck the zero and span adjustments
by repeating steps 2.4.7 and 2.4.8.2. Record the NOX
concentration and the analyzer's NOX response.
2.4.8.3 Generate several additional concentrations (at least five
evenly spaced points across the remaining scale are suggested to verify
linearity) by decreasing FNO or increasing FD. For each
concentration generated, calculate the exact NO and NOX
concentrations using equations (16) and (18) respectively. Record the
analyzer's NO and NOX responses for each concentration. Plot
the analyzer responses versus the respective calculated NO and
NOX concentrations and draw or calculate the NO and
NOX calibration curves. For subsequent calibrations where
linearity can be assumed, these curves may be checked with a two-point
calibration consisting of a zero point and NO and NOX
concentrations of approximately 80 percent of the URL.
2.4.9 Preparation of NO2 calibration curve.
2.4.9.1 Remove the NO flow. Assuming the NO2 zero has
been properly adjusted while sampling zero air in step 2.4.7, switch the
valve to provide NO2 at the output manifold.
2.4.9.2 Adjust FD to generate an NO2 concentration of
approximately 80 percent of the URL of the NO2 range. The
total air flow must exceed the demand of the analyzer(s) under
calibration. The actual concentration of NO2 is calculated
from:
[GRAPHIC] [TIFF OMITTED] TR31AU93.054
where:
[NO2]OUT = diluted NO2 concentration at
the output manifold, ppm
R = permeation rate, [micro]g/min
K = 0.532 [micro]l NO2/[micro]g NO2 (at 25 [deg]C
and 760 mm Hg)
Fp = air flowrate across permeation device, scm\3\/min
FD = diluent air flowrate, scm\3\/min
[[Page 53]]
Sample this NO2 concentration until the NOX and
NO2 responses have stabilized. Adjust the NO2 span
control to obtain a recorder response as indicated below:
recorder response (% scale)
[GRAPHIC] [TIFF OMITTED] TR31AU93.055
Note: If the analyzer has only one or two span controls, the span
adjustments are made on the NO channel or NO and NOX channels
and no further adjustment is made here for NO2.
If substantial adjustment of the NO2 span control is
necessary it may be necessary to recheck the zero and span adjustments
by repeating steps 2.4.7 and 2.4.9.2. Record the NO2
concentration and the analyzer's NO2 response. Using the
NOX calibration curve obtained in step 2.4.8, measure and
record the NOX concentration as [NOX]M.
2.4.9.3 Adjust FD to obtain several other concentrations of
NO2 over the NO2 range (at least five evenly
spaced points across the remaining scale are suggested). Calculate each
NO2 concentration using equation (20) and record the
corresponding analyzer NO2 and NOX responses. Plot
the analyzer's NO2 responses versus the corresponding
calculated NO2 concentrations and draw or calculate the
NO2 calibration curve.
2.4.10 Determination of converter efficiency.
2.4.10.1 Plot [NOX]M (y-axis) versus
[NO2]OUT (x-axis) and draw or calculate the
converter efficiency curve. The slope of the curve times 100 is the
average converter efficiency, EC. The average converter efficiency must
be greater than 96 percent; if it is less than 96 percent, replace or
service the converter.
Note: Supplemental information on calibration and other procedures
in this method are given in reference 13.
3. Frequency of calibration. The frequency of calibration, as well
as the number of points necessary to establish the calibration curve and
the frequency of other performance checks, will vary from one analyzer
to another. The user's quality control program should provide guidelines
for initial establishment of these variables and for subsequent
alteration as operational experience is accumulated. Manufacturers of
analyzers should include in their instruction/operation manuals
information and guidance as to these variables and on other matters of
operation, calibration, and quality control.
References
1. A. Fontijn, A. J. Sabadell, and R. J. Ronco, ``Homogeneous
Chemiluminescent Measurement of Nitric Oxide with Ozone,'' Anal. Chem.,
42, 575 (1970).
2. D. H. Stedman, E. E. Daby, F. Stuhl, and H. Niki, ``Analysis of
Ozone and Nitric Oxide by a Chemiluminiscent Method in Laboratory and
Atmospheric Studies of Photochemical Smog,'' J. Air Poll. Control
Assoc., 22, 260 (1972).
3. B. E. Martin, J. A. Hodgeson, and R. K. Stevens, ``Detection of
Nitric Oxide Chemiluminescence at Atmospheric Pressure,'' Presented at
164th National ACS Meeting, New York City, August 1972.
4. J. A. Hodgeson, K. A. Rehme, B. E. Martin, and R. K. Stevens,
``Measurements for Atmospheric Oxides of Nitrogen and Ammonia by
Chemiluminescence,'' Presented at 1972 APCA Meeting, Miami, FL, June
1972.
5. R. K. Stevens and J. A. Hodgeson, ``Applications of
Chemiluminescence Reactions to the Measurement of Air Pollutants,''
Anal. Chem., 45, 443A (1973).
6. L. P. Breitenbach and M. Shelef, ``Development of a Method for
the Analysis of NO2 and NH3 by NO-Measuring
Instruments,'' J. Air Poll. Control Assoc., 23, 128 (1973).
7. A. M. Winer, J. W. Peters, J. P. Smith, and J. N. Pitts, Jr.,
``Response of Commercial Chemiluminescent NO-NO2 Analyzers to
Other Nitrogen-Containing Compounds,'' Environ. Sci. Technol., 8, 1118
(1974).
8. K. A. Rehme, B. E. Martin, and J. A. Hodgeson, Tentative Method
for the Calibration of Nitric Oxide, Nitrogen Dioxide, and Ozone
Analyzers by Gas Phase Titration,'' EPA-R2-73-246, March 1974.
9. J. A. Hodgeson, R. K. Stevens, and B. E. Martin, ``A Stable Ozone
Source Applicable as a Secondary Standard for Calibration of Atmospheric
Monitors,'' ISA Transactions, 11, 161 (1972).
10. A. E. O'Keeffe and G. C. Ortman, ``Primary Standards for Trace
Gas Analysis,'' Anal. Chem., 38, 760 (1966).
11. F. P. Scaringelli, A. E. O'Keeffe, E. Rosenberg, and J. P. Bell,
``Preparation of Known Concentrations of Gases and Vapors with
Permeation Devices Calibrated Gravimetrically,'' Anal. Chem., 42, 871
(1970).
12. H. L. Rook, E. E. Hughes, R. S. Fuerst, and J. H. Margeson,
``Operation Characteristics of NO2 Permeation Devices,''
Presented at 167th National ACS Meeting, Los Angeles, CA, April 1974.
13. E. C. Ellis, ``Technical Assistance Document for the
Chemiluminescence Measurement of Nitrogen Dioxide,'' EPA-E600/4-75-003
(Available in draft form from the United States Environmental Protection
Agency, Department E (MD-76), Environmental Monitoring and Support
Laboratory, Research Triangle Park, NC 27711).
14. A Procedure for Establishing Traceability of Gas Mixtures to
Certain National Bureau of Standards Standard Reference Materials. EPA-
600/7-81-010, Joint publication by NBS and EPA. Available from the U.S.
Environmental Protection Agency, Environmental Monitoring Systems
Laboratory (MD-77), Research Triangle Park, NC 27711, May 1981.
[[Page 54]]
15. Quality Assurance Handbook for Air Pollution Measurement
Systems, Volume II, Ambient Air Specific Methods. The U.S. Environmental
Protection Agency, Environmental Monitoring Systems Laboratory, Research
Triangle Park, NC 27711. Publication No. EAP-600/4-77-027a.
[[Page 55]]
[41 FR 52688, Dec. 1, 1976, as amended at 48 FR 2529, Jan 20, 1983]
Appendix G to Part 50--Reference Method for the Determination of Lead in
Suspended Particulate Matter Collected From Ambient Air
1. Principle and applicability.
1.1 Ambient air suspended particulate matter is collected on a
glass-fiber filter for 24 hours using a high volume air sampler. The
analysis of the 24-hour samples may be performed for either individual
samples or composites of the samples collected over a calendar month or
quarter, provided that the compositing procedure has been approved in
accordance with section 2.8 of appendix C to part 58 of this chapter--
Modifications of methods by users. (Guidance or assistance in requesting
approval under Section 2.8 can be obtained from the address given in
section 2.7 of appendix C to part 58 of this chapter.)
1.2 Lead in the particulate matter is solubilized by extraction with
nitric acid (HNO3), facilitated by heat or by a mixture of
HNO3 and hydrochloric acid (HCl) facilitated by
ultrasonication.
1.3 The lead content of the sample is analyzed by atomic absorption
spectrometry using an air-acetylene flame, the 283.3 or 217.0 nm lead
absorption line, and the optimum instrumental conditions recommended by
the manufacturer.
1.4 The ultrasonication extraction with HNO3/HCl will
extract metals other than lead from ambient particulate matter.
2. Range, sensitivity, and lower detectable limit. The values given
below are typical of the methods capabilities. Absolute values will vary
for individual situations depending on the type of instrument used, the
lead line, and operating conditions.
2.1 Range. The typical range of the method is 0.07 to 7.5 [micro]g
Pb/m\3\ assuming an upper linear range of analysis of 15 [micro]g/ml and
an air volume of 2,400 m\3\.
2.2 Sensitivity. Typical sensitivities for a 1 percent change in
absorption (0.0044 absorbance units) are 0.2 and 0.5 [micro]g Pb/ml for
the 217.0 and 283.3 nm lines, respectively.
2.3 Lower detectable limit (LDL). A typical LDL is 0.07 [micro]g Pb/
m\3\. The above value was calculated by doubling the between-laboratory
standard deviation obtained for the lowest measurable lead concentration
in a collaborative test of the method.(15) An air volume of 2,400 m\3\
was assumed.
3. Interferences. Two types of interferences are possible: chemical
and light scattering.
3.1 Chemical. Reports on the absence (1, 2, 3, 4, 5) of chemical
interferences far outweigh those reporting their presence, (6)
therefore, no correction for chemical interferences is given here. If
the analyst suspects that the sample matrix is causing a chemical
interference, the interference can be verified and corrected for by
carrying out the analysis
[[Page 56]]
with and without the method of standard additions.(7)
3.2 Light scattering. Nonatomic absorption or light scattering,
produced by high concentrations of dissolved solids in the sample, can
produce a significant interference, especially at low lead
concentrations. (2) The interference is greater at the 217.0 nm line
than at the 283.3 nm line. No interference was observed using the 283.3
nm line with a similar method.(1)
Light scattering interferences can, however, be corrected for
instrumentally. Since the dissolved solids can vary depending on the
origin of the sample, the correction may be necessary, especially when
using the 217.0 nm line. Dual beam instruments with a continuum source
give the most accurate correction. A less accurate correction can be
obtained by using a nonabsorbing lead line that is near the lead
analytical line. Information on use of these correction techniques can
be obtained from instrument manufacturers' manuals.
If instrumental correction is not feasible, the interference can be
eliminated by use of the ammonium pyrrolidinecarbodithioate-
methylisobutyl ketone, chelation-solvent extraction technique of sample
preparation.(8)
4. Precision and bias.
4.1 The high-volume sampling procedure used to collect ambient air
particulate matter has a between-laboratory relative standard deviation
of 3.7 percent over the range 80 to 125 [micro]g/m\3\.(9) The combined
extraction-analysis procedure has an average within-laboratory relative
standard deviation of 5 to 6 percent over the range 1.5 to 15 [micro]g
Pb/ml, and an average between laboratory relative standard deviation of
7 to 9 percent over the same range. These values include use of either
extraction procedure.
4.2 Single laboratory experiments and collaborative testing indicate
that there is no significant difference in lead recovery between the hot
and ultrasonic extraction procedures.(15)
5. Apparatus.
5.1 Sampling.
5.1.1 High-Volume Sampler. Use and calibrate the sampler as
described in appendix B to this part.
5.2 Analysis.
5.2.1 Atomic absorption spectrophotometer. Equipped with lead hollow
cathode or electrodeless discharge lamp.
5.2.1.1 Acetylene. The grade recommended by the instrument
manufacturer should be used. Change cylinder when pressure drops below
50-100 psig.
5.2.1.2 Air. Filtered to remove particulate, oil, and water.
5.2.2 Glassware. Class A borosilicate glassware should be used
throughout the analysis.
5.2.2.1 Beakers. 30 and 150 ml. graduated, Pyrex.
5.2.2.2 Volumetric flasks. 100-ml.
5.2.2.3 Pipettes. To deliver 50, 30, 15, 8, 4, 2, 1 ml.
5.2.2.4 Cleaning. All glassware should be scrupulously cleaned. The
following procedure is suggested. Wash with laboratory detergent, rinse,
soak for 4 hours in 20 percent (w/w) HNO3, rinse 3 times with
distilled-deionized water, and dry in a dust free manner.
5.2.3 Hot plate.
5.2.4. Ultrasonication water bath, unheated. Commercially available
laboratory ultrasonic cleaning baths of 450 watts or higher ``cleaning
power,'' i.e., actual ultrasonic power output to the bath have been
found satisfactory.
5.2.5 Template. To aid in sectioning the glass-fiber filter. See
figure 1 for dimensions.
5.2.6 Pizza cutter. Thin wheel. Thickness 1mm.
5.2.7 Watch glass.
5.2.8 Polyethylene bottles. For storage of samples. Linear
polyethylene gives better storage stability than other polyethylenes and
is preferred.
5.2.9 Parafilm ``M''.\1\ American Can Co., Marathon Products,
Neenah, Wis., or equivalent.
---------------------------------------------------------------------------
\1\ Mention of commercial products does not imply endorsement by the
U.S. Environmental Protection Agency.
---------------------------------------------------------------------------
6. Reagents.
6.1 Sampling.
6.1.1 Glass fiber filters. The specifications given below are
intended to aid the user in obtaining high quality filters with
reproducible properties. These specifications have been met by EPA
contractors.
6.1.1.1 Lead content. The absolute lead content of filters is not
critical, but low values are, of course, desirable. EPA typically
obtains filters with a lead content of 75 [micro]g/filter.
It is important that the variation in lead content from filter to
filter, within a given batch, be small.
6.1.1.2 Testing.
6.1.1.2.1 For large batches of filters (500 filters)
select at random 20 to 30 filters from a given batch. For small batches
(500 filters) a lesser number of filters may be taken. Cut
one \3/4\x8 strip from each filter anywhere in the
filter. Analyze all strips, separately, according to the directions in
sections 7 and 8.
6.1.1.2.2 Calculate the total lead in each filter as
[GRAPHIC] [TIFF OMITTED] TC08NO91.084
where:
Fb = Amount of lead per 72 square inches of filter, [micro]g.
6.1.1.2.3 Calculate the mean, Fb, of the values and the
relative standard deviation
[[Page 57]]
(standard deviation/mean x 100). If the relative standard deviation is
high enough so that, in the analysts opinion, subtraction of
Fb, (section 10.3) may result in a significant error in the
[micro]g Pb/m\3\, the batch should be rejected.
6.1.1.2.4 For acceptable batches, use the value of Fb to
correct all lead analyses (section 10.3) of particulate matter collected
using that batch of filters. If the analyses are below the LDL (section
2.3) no correction is necessary.
6.2 Analysis.
6.2.1 Concentrated (15.6 M) HNO3. ACS reagent grade
HNO3 and commercially available redistilled HNO3
has found to have sufficiently low lead concentrations.
6.2.2 Concentrated (11.7 M) HCl. ACS reagent grade.
6.2.3 Distilled-deionized water. (D.I. water).
6.2.4 3 M HNO3. This solution is used in the hot
extraction procedure. To prepare, add 192 ml of concentrated
HNO3 to D.I. water in a 1 l volumetric flask. Shake well,
cool, and dilute to volume with D.I. water. Caution: Nitric acid fumes
are toxic. Prepare in a well ventilated fume hood.
6.2.5 0.45 M HNO3. This solution is used as the matrix
for calibration standards when using the hot extraction procedure. To
prepare, add 29 ml of concentrated HNO3 to D.I. water in a 1
l volumetric flask. Shake well, cool, and dilute to volume with D.I.
water.
6.2.6 2.6 M HNO3+0 to 0.9 M HCl. This solution is used in
the ultrasonic extraction procedure. The concentration of HCl can be
varied from 0 to 0.9 M. Directions are given for preparation of a 2.6 M
HNO3+0.9 M HCl solution. Place 167 ml of concentrated
HNO3 into a 1 l volumetric flask and add 77 ml of
concentrated HCl. Stir 4 to 6 hours, dilute to nearly 1 l with D.I.
water, cool to room temperature, and dilute to 1 l.
6.2.7 0.40 M HNO3 + X M HCl. This solution is used as the
matrix for calibration standards when using the ultrasonic extraction
procedure. To prepare, add 26 ml of concentrated HNO3, plus
the ml of HCl required, to a 1 l volumetric flask. Dilute to nearly 1 l
with D.I. water, cool to room temperature, and dilute to 1 l. The amount
of HCl required can be determined from the following equation:
[GRAPHIC] [TIFF OMITTED] TC08NO91.085
where:
y = ml of concentrated HCl required.
x = molarity of HCl in 6.2.6.
0.15 = dilution factor in 7.2.2.
6.2.8 Lead nitrate, Pb(NO3)2. ACS reagent
grade, purity 99.0 percent. Heat for 4 hours at 120 [deg]C and cool in a
desiccator.
6.3 Calibration standards.
6.3.1 Master standard, 1000 [micro]g Pb/ml in HNO3.
Dissolve 1.598 g of Pb(NO3)2 in 0.45 M
HNO3 contained in a 1 l volumetric flask and dilute to volume
with 0.45 M HNO3.
6.3.2 Master standard, 1000 [micro]g Pb/ml in HNO3/HCl.
Prepare as in section 6.3.1 except use the HNO3/HCl solution
in section 6.2.7.
Store standards in a polyethylene bottle. Commercially available
certified lead standard solutions may also be used.
7. Procedure.
7.1 Sampling. Collect samples for 24 hours using the procedure
described in reference 10 with glass-fiber filters meeting the
specifications in section 6.1.1. Transport collected samples to the
laboratory taking care to minimize contamination and loss of sample.
(16).
7.2 Sample preparation.
7.2.1 Hot extraction procedure.
7.2.1.1 Cut a \3/4\x8 strip from the exposed
filter using a template and a pizza cutter as described in Figures 1 and
2. Other cutting procedures may be used.
Lead in ambient particulate matter collected on glass fiber filters
has been shown to be uniformly distributed across the filter. \1,3,11\
Another study \12\ has shown that when sampling near a roadway, strip
position contributes significantly to the overall variability associated
with lead analyses. Therefore, when sampling near a roadway, additional
strips should be analyzed to minimize this variability.
7.2.1.2 Fold the strip in half twice and place in a 150-ml beaker.
Add 15 ml of 3 M HNO3 to cover the sample. The acid should
completely cover the sample. Cover the beaker with a watch glass.
7.2.1.3 Place beaker on the hot-plate, contained in a fume hood, and
boil gently for 30 min. Do not let the sample evaporate to dryness.
Caution: Nitric acid fumes are toxic.
7.2.1.4 Remove beaker from hot plate and cool to near room
temperature.
7.2.1.5 Quantitatively transfer the sample as follows:
7.2.1.5.1 Rinse watch glass and sides of beaker with D.I. water.
7.2.1.5.2 Decant extract and rinsings into a 100-ml volumetric
flask.
7.2.1.5.3 Add D.I. water to 40 ml mark on beaker, cover with watch
glass, and set aside for a minimum of 30 minutes. This is a critical
step and cannot be omitted since it allows the HNO3 trapped
in the filter to diffuse into the rinse water.
7.2.1.5.4 Decant the water from the filter into the volumetric
flask.
7.2.1.5.5 Rinse filter and beaker twice with D.I. water and add
rinsings to volumetric flask until total volume is 80 to 85 ml.
7.2.1.5.6 Stopper flask and shake vigorously. Set aside for
approximately 5 minutes or until foam has dissipated.
7.2.1.5.7 Bring solution to volume with D.I. water. Mix thoroughly.
[[Page 58]]
7.2.1.5.8 Allow solution to settle for one hour before proceeding
with analysis.
7.2.1.5.9 If sample is to be stored for subsequent analysis,
transfer to a linear polyethylene bottle.
7.2.2 Ultrasonic extraction procedure.
7.2.2.1 Cut a \3/4\x8 strip from the exposed
filter as described in section 7.2.1.1.
7.2.2.2 Fold the strip in half twice and place in a 30 ml beaker.
Add 15 ml of the HNO3/HCl solution in section 6.2.6. The acid
should completely cover the sample. Cover the beaker with parafilm.
The parafilm should be placed over the beaker such that none of the
parafilm is in contact with water in the ultrasonic bath. Otherwise,
rinsing of the parafilm (section 7.2.2.4.1) may contaminate the sample.
7.2.2.3 Place the beaker in the ultrasonication bath and operate for
30 minutes.
7.2.2.4 Quantitatively transfer the sample as follows:
7.2.2.4.1 Rinse parafilm and sides of beaker with D.I. water.
7.2.2.4.2 Decant extract and rinsings into a 100 ml volumetric
flask.
7.2.2.4.3 Add 20 ml D.I. water to cover the filter strip, cover with
parafilm, and set aside for a minimum of 30 minutes. This is a critical
step and cannot be omitted. The sample is then processed as in sections
7.2.1.5.4 through 7.2.1.5.9.
Note: Samples prepared by the hot extraction procedure are now in
0.45 M HNO3. Samples prepared by the ultrasonication
procedure are in 0.40 M HNO3 + X M HCl.
8. Analysis.
8.1 Set the wavelength of the monochromator at 283.3 or 217.0 nm.
Set or align other instrumental operating conditions as recommended by
the manufacturer.
8.2 The sample can be analyzed directly from the volumetric flask,
or an appropriate amount of sample decanted into a sample analysis tube.
In either case, care should be taken not to disturb the settled solids.
8.3 Aspirate samples, calibration standards and blanks (section 9.2)
into the flame and record the equilibrium absorbance.
8.4 Determine the lead concentration in [micro]g Pb/ml, from the
calibration curve, section 9.3.
8.5 Samples that exceed the linear calibration range should be
diluted with acid of the same concentration as the calibration standards
and reanalyzed.
9. Calibration.
9.1 Working standard, 20 [micro]g Pb/ml. Prepared by diluting 2.0 ml
of the master standard (section 6.3.1 if the hot acid extraction was
used or section 6.3.2 if the ultrasonic extraction procedure was used)
to 100 ml with acid of the same concentration as used in preparing the
master standard.
9.2 Calibration standards. Prepare daily by diluting the working
standard, with the same acid matrix, as indicated below. Other lead
concentrations may be used.
------------------------------------------------------------------------
Concentration
Volume of 20 [micro]g/ml working standard, ml Final [micro]g Pb/
volume, ml ml
------------------------------------------------------------------------
0............................................ 100 0
1.0.......................................... 200 0.1
2.0.......................................... 200 0.2
2.0.......................................... 100 0.4
4.0.......................................... 100 0.8
8.0.......................................... 100 1.6
15.0......................................... 100 3.0
30.0......................................... 100 6.0
50.0......................................... 100 10.0
100.0........................................ 100 20.0
------------------------------------------------------------------------
9.3 Preparation of calibration curve. Since the working range of
analysis will vary depending on which lead line is used and the type of
instrument, no one set of instructions for preparation of a calibration
curve can be given. Select standards (plus the reagent blank), in the
same acid concentration as the samples, to cover the linear absorption
range indicated by the instrument manufacturer. Measure the absorbance
of the blank and standards as in section 8.0. Repeat until good
agreement is obtained between replicates. Plot absorbance (y-axis)
versus concentration in [micro]g Pb/ml (x-axis). Draw (or compute) a
straight line through the linear portion of the curve. Do not force the
calibration curve through zero. Other calibration procedures may be
used.
To determine stability of the calibration curve, remeasure--
alternately--one of the following calibration standards for every 10th
sample analyzed: Concentration <=1 [micro]g Pb/ml; concentration <=10
[micro]g Pb/ml. If either standard deviates by more than 5 percent from
the value predicted by the calibration curve, recalibrate and repeat the
previous 10 analyses.
10. Calculation.
10.1 Measured air volume. Calculate the measured air volume at
Standard Temperature and Pressure as described in Reference 10.
10.2 Lead concentration. Calculate lead concentration in the air
sample.
[[Page 59]]
where:
C = Concentration, [micro]g Pb/sm\3\.
[micro]g Pb/ml = Lead concentration determined from section 8.
100 ml/strip = Total sample volume.
12 strips = Total useable filter area, 8x9.
Exposed area of one strip, \3/4\x7.
Filter = Total area of one strip, \3/4\x8.
Fb = Lead concentration of blank filter, [micro]g, from
section 6.1.1.2.3.
VSTP = Air volume from section 10.2.
11. Quality control.
\3/4\x8 glass fiber filter strips containing
80 to 2000 [micro]g Pb/strip (as lead salts) and blank strips with zero
Pb content should be used to determine if the method--as being used--has
any bias. Quality control charts should be established to monitor
differences between measured and true values. The frequency of such
checks will depend on the local quality control program.
To minimize the possibility of generating unreliable data, the user
should follow practices established for assuring the quality of air
pollution data, (13) and take part in EPA's semiannual audit program for
lead analyses.
12. Trouble shooting.
1. During extraction of lead by the hot extraction procedure, it is
important to keep the sample covered so that corrosion products--formed
on fume hood surfaces which may contain lead--are not deposited in the
extract.
2. The sample acid concentration should minimize corrosion of the
nebulizer. However, different nebulizers may require lower acid
concentrations. Lower concentrations can be used provided samples and
standards have the same acid concentration.
3. Ashing of particulate samples has been found, by EPA and
contractor laboratories, to be unnecessary in lead analyses by atomic
absorption. Therefore, this step was omitted from the method.
4. Filtration of extracted samples, to remove particulate matter,
was specifically excluded from sample preparation, because some analysts
have observed losses of lead due to filtration.
5. If suspended solids should clog the nebulizer during analysis of
samples, centrifuge the sample to remove the solids.
13. Authority.
(Secs. 109 and 301(a), Clean Air Act, as amended (42 U.S.C. 7409,
7601(a)))
14. References.
1. Scott, D. R. et al. ``Atomic Absorption and Optical Emission
Analysis of NASN Atmospheric Particulate Samples for Lead.'' Envir. Sci.
and Tech., 10, 877-880 (1976).
2. Skogerboe, R. K. et al. ``Monitoring for Lead in the
Environment.'' pp. 57-66, Department of Chemistry, Colorado State
University, Fort Collins, CO 80523. Submitted to National Science
Foundation for publications, 1976.
3. Zdrojewski, A. et al. ``The Accurate Measurement of Lead in
Airborne Particulates.'' Inter. J. Environ. Anal. Chem., 2, 63-77
(1972).
4. Slavin, W., ``Atomic Absorption Spectroscopy.'' Published by
Interscience Company, New York, NY (1968).
5. Kirkbright, G. F., and Sargent, M., ``Atomic Absorption and
Fluorescence Spectroscopy.'' Published by Academic Press, New York, NY
1974.
6. Burnham, C. D. et al., ``Determination of Lead in Airborne
Particulates in Chicago and Cook County, IL, by Atomic Absorption
Spectroscopy.'' Envir. Sci. and Tech., 3, 472-475 (1969).
7. ``Proposed Recommended Practices for Atomic Absorption
Spectrometry.'' ASTM Book of Standards, part 30, pp. 1596-1608 (July
1973).
8. Koirttyohann, S. R. and Wen, J. W., ``Critical Study of the APCD-
MIBK Extraction System for Atomic Absorption.'' Anal. Chem., 45, 1986-
1989 (1973).
9. Collaborative Study of Reference Method for the Determination of
Suspended Particulates in the Atmosphere (High Volume Method).
Obtainable from National Technical Information Service, Department of
Commerce, Port Royal Road, Springfield, VA 22151, as PB-205-891.
10. [Reserved]
11. Dubois, L., et al., ``The Metal Content of Urban Air.'' JAPCA,
16, 77-78 (1966).
12. EPA Report No. 600/4-77-034, June 1977, ``Los Angeles Catalyst
Study Symposium.'' Page 223.
13. Quality Assurance Handbook for Air Pollution Measurement System.
Volume 1--Principles. EPA-600/9-76-005, March 1976.
14. Thompson, R. J. et al., ``Analysis of Selected Elements in
Atmospheric Particulate Matter by Atomic Absorption.'' Atomic Absorption
Newsletter, 9, No. 3, May-June 1970.
15. To be published. EPA, QAB, EMSL, RTP, N.C. 27711
[[Page 60]]
16. Quality Assurance Handbook for Air Pollution Measurement
Systems. Volume II--Ambient Air Specific Methods. EPA-600/4-77/027a, May
1977.
[[Page 61]]
(Secs. 109, 301(a) of the Clean Air Act, as amended (42 U.S.C. 7409,
7601(a)); secs. 110, 301(a) and 319 of the Clean Air Act (42 U.S.C.
7410, 7601(a), 7619))
[43 FR 46258, Oct. 5, 1978; 44 FR 37915, June 29, 1979, as amended at 46
FR 44163, Sept. 3, 1981; 52 FR 24664, July 1, 1987]
Appendix H to Part 50--Interpretation of the 1-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone
1. General
This appendix explains how to determine when the expected number of
days per calendar year with maximum hourly average concentrations above
0.12 ppm (235 [micro]g/m\3\) is equal to or less than 1. An expanded
discussion of these procedures and associated examples are contained in
the ``Guideline for Interpretation of Ozone Air Quality Standards.'' For
purposes of clarity in the following discussion, it is convenient to use
the term ``exceedance'' to describe a daily maximum hourly average ozone
measurement that is greater than the level of the standard. Therefore,
the phrase ``expected number of days with maximum hourly average ozone
concentrations above the level of the standard'' may be simply stated as
the ``expected number of exceedances.''
[[Page 62]]
The basic principle in making this determination is relatively
straightforward. Most of the complications that arise in determining the
expected number of annual exceedances relate to accounting for
incomplete sampling. In general, the average number of exceedances per
calendar year must be less than or equal to 1. In its simplest form, the
number of exceedances at a monitoring site would be recorded for each
calendar year and then averaged over the past 3 calendar years to
determine if this average is less than or equal to 1.
2. Interpretation of Expected Exceedances
The ozone standard states that the expected number of exceedances
per year must be less than or equal to 1. The statistical term
``expected number'' is basically an arithmetic average. The following
example explains what it would mean for an area to be in compliance with
this type of standard. Suppose a monitoring station records a valid
daily maximum hourly average ozone value for every day of the year
during the past 3 years. At the end of each year, the number of days
with maximum hourly concentrations above 0.12 ppm is determined and this
number is averaged with the results of previous years. As long as this
average remains ``less than or equal to 1,'' the area is in compliance.
3. Estimating the Number of Exceedances for a Year
In general, a valid daily maximum hourly average value may not be
available for each day of the year, and it will be necessary to account
for these missing values when estimating the number of exceedances for a
particular calendar year. The purpose of these computations is to
determine if the expected number of exceedances per year is less than or
equal to 1. Thus, if a site has two or more observed exceedances each
year, the standard is not met and it is not necessary to use the
procedures of this section to account for incomplete sampling.
The term ``missing value'' is used here in the general sense to
describe all days that do not have an associated ozone measurement. In
some cases, a measurement might actually have been missed but in other
cases no measurement may have been scheduled for that day. A daily
maximum ozone value is defined to be the highest hourly ozone value
recorded for the day. This daily maximum value is considered to be valid
if 75 percent of the hours from 9:01 a.m. to 9:00 p.m. (LST) were
measured or if the highest hour is greater than the level of the
standard.
In some areas, the seasonal pattern of ozone is so pronounced that
entire months need not be sampled because it is extremely unlikely that
the standard would be exceeded. Any such waiver of the ozone monitoring
requirement would be handled under provisions of 40 CFR, part 58. Some
allowance should also be made for days for which valid daily maximum
hourly values were not obtained but which would quite likely have been
below the standard. Such an allowance introduces a complication in that
it becomes necessary to define under what conditions a missing value may
be assumed to have been less than the level of the standard. The
following criterion may be used for ozone:
A missing daily maximum ozone value may be assumed to be less than
the level of the standard if the valid daily maxima on both the
preceding day and the following day do not exceed 75 percent of the
level of the standard.
Let z denote the number of missing daily maximum values that may be
assumed to be less than the standard. Then the following formula shall
be used to estimate the expected number of exceedances for the year:
[GRAPHIC] [TIFF OMITTED] TC08NO91.086
(*Indicates multiplication.)
where:
e = the estimated number of exceedances for the year,
N = the number of required monitoring days in the year,
n = the number of valid daily maxima,
v = the number of daily values above the level of the standard, and
z = the number of days assumed to be less than the standard level.
This estimated number of exceedances shall be rounded to one decimal
place (fractional parts equal to 0.05 round up).
It should be noted that N will be the total number of days in the
year unless the appropriate Regional Administrator has granted a waiver
under the provisions of 40 CFR part 58.
The above equation may be interpreted intuitively in the following
manner. The estimated number of exceedances is equal to the observed
number of exceedances (v) plus an increment that accounts for incomplete
sampling. There were (N-n) missing values for the year but a certain
number of these, namely z, were assumed to be less than the standard.
Therefore, (N-n-z) missing values are considered to include possible
exceedances. The fraction of measured values that are above the level of
the standard is v/n. It is assumed that this same fraction applies to
the (N-n-z) missing values and that (v/n)*(N-n-z) of these values would
also have exceeded the level of the standard.
[44 FR 8220, Feb. 8, 1979, as amended at 62 FR 38895, July 18, 1997]
[[Page 63]]
Appendix I to Part 50--Interpretation of the 8-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone
1. General.
This appendix explains the data handling conventions and
computations necessary for determining whether the national 8-hour
primary and secondary ambient air quality standards for ozone specified
in Sec. 50.10 are met at an ambient ozone air quality monitoring site.
Ozone is measured in the ambient air by a reference method based on
appendix D of this part. Data reporting, data handling, and computation
procedures to be used in making comparisons between reported ozone
concentrations and the level of the ozone standard are specified in the
following sections. Whether to exclude, retain, or make adjustments to
the data affected by stratospheric ozone intrusion or other natural
events is subject to the approval of the appropriate Regional
Administrator.
2. Primary and Secondary Ambient Air Quality Standards for Ozone.
2.1 Data Reporting and Handling Conventions.
2.1.1 Computing 8-hour averages. Hourly average concentrations shall
be reported in parts per million (ppm) to the third decimal place, with
additional digits to the right being truncated. Running 8-hour averages
shall be computed from the hourly ozone concentration data for each hour
of the year and the result shall be stored in the first, or start, hour
of the 8-hour period. An 8-hour average shall be considered valid if at
least 75% of the hourly averages for the 8-hour period are available. In
the event that only 6 (or 7) hourly averages are available, the 8-hour
average shall be computed on the basis of the hours available using 6
(or 7) as the divisor. (8-hour periods with three or more missing hours
shall not be ignored if, after substituting one-half the minimum
detectable limit for the missing hourly concentrations, the 8-hour
average concentration is greater than the level of the standard.) The
computed 8-hour average ozone concentrations shall be reported to three
decimal places (the insignificant digits to the right of the third
decimal place are truncated, consistent with the data handling
procedures for the reported data.)
2.1.2 Daily maximum 8-hour average concentrations. (a) There are 24
possible running 8-hour average ozone concentrations for each calendar
day during the ozone monitoring season. (Ozone monitoring seasons vary
by geographic location as designated in part 58, appendix D to this
chapter.) The daily maximum 8-hour concentration for a given calendar
day is the highest of the 24 possible 8-hour average concentrations
computed for that day. This process is repeated, yielding a daily
maximum 8-hour average ozone concentration for each calendar day with
ambient ozone monitoring data. Because the 8-hour averages are recorded
in the start hour, the daily maximum 8-hour concentrations from two
consecutive days may have some hourly concentrations in common.
Generally, overlapping daily maximum 8-hour averages are not likely,
except in those non-urban monitoring locations with less pronounced
diurnal variation in hourly concentrations.
(b) An ozone monitoring day shall be counted as a valid day if valid
8-hour averages are available for at least 75% of possible hours in the
day (i.e., at least 18 of the 24 averages). In the event that less than
75% of the 8-hour averages are available, a day shall also be counted as
a valid day if the daily maximum 8-hour average concentration for that
day is greater than the level of the ambient standard.
2.2 Primary and Secondary Standard-related Summary Statistic. The
standard-related summary statistic is the annual fourth-highest daily
maximum 8-hour ozone concentration, expressed in parts per million,
averaged over three years. The 3-year average shall be computed using
the three most recent, consecutive calendar years of monitoring data
meeting the data completeness requirements described in this appendix.
The computed 3-year average of the annual fourth-highest daily maximum
8-hour average ozone concentrations shall be expressed to three decimal
places (the remaining digits to the right are truncated.)
2.3 Comparisons with the Primary and Secondary Ozone Standards. (a)
The primary and secondary ozone ambient air quality standards are met at
an ambient air quality monitoring site when the 3-year average of the
annual fourth-highest daily maximum 8-hour average ozone concentration
is less than or equal to 0.08 ppm. The number of significant figures in
the level of the standard dictates the rounding convention for comparing
the computed 3-year average annual fourth-highest daily maximum 8-hour
average ozone concentration with the level of the standard. The third
decimal place of the computed value is rounded, with values equal to or
greater than 5 rounding up. Thus, a computed 3-year average ozone
concentration of 0.085 ppm is the smallest value that is greater than
0.08 ppm.
(b) This comparison shall be based on three consecutive, complete
calendar years of air quality monitoring data. This requirement is met
for the three year period at a monitoring site if daily maximum 8-hour
average concentrations are available for at least 90%, on average, of
the days during the designated ozone monitoring season, with a minimum
data completeness in any one year of at least 75% of the designated
sampling days. When
[[Page 64]]
computing whether the minimum data completeness requirements have been
met, meteorological or ambient data may be sufficient to demonstrate
that meteorological conditions on missing days were not conducive to
concentrations above the level of the standard. Missing days assumed
less than the level of the standard are counted for the purpose of
meeting the data completeness requirement, subject to the approval of
the appropriate Regional Administrator.
(c) Years with concentrations greater than the level of the standard
shall not be ignored on the ground that they have less than complete
data. Thus, in computing the 3-year average fourth maximum
concentration, calendar years with less than 75% data completeness shall
be included in the computation if the average annual fourth maximum 8-
hour concentration is greater than the level of the standard.
(d) Comparisons with the primary and secondary ozone standards are
demonstrated by examples 1 and 2 in paragraphs (d)(1) and (d) (2)
respectively as follows:
(1) As shown in example 1, the primary and secondary standards are
met at this monitoring site because the 3-year average of the annual
fourth-highest daily maximum 8-hour average ozone concentrations (i.e.,
0.084 ppm) is less than or equal to 0.08 ppm. The data completeness
requirement is also met because the average percent of days with valid
ambient monitoring data is greater than 90%, and no single year has less
than 75% data completeness.
Example 1. Ambient monitoring site attaining the primary and secondary ozone standards
----------------------------------------------------------------------------------------------------------------
1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest
Percent Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
Year Valid Days hour Conc. hour Conc. hour Conc. hour Conc. hour Conc.
(ppm) (ppm) (ppm) (ppm) (ppm)
----------------------------------------------------------------------------------------------------------------
1993.............................. 100% 0.092 0.091 0.090 0.088 0.085
----------------------------------------------------------------------------------------------------------------
1994.............................. 96% 0.090 0.089 0.086 0.084 0.080
----------------------------------------------------------------------------------------------------------------
1995.............................. 98% 0.087 0.085 0.083 0.080 0.075
================================================================================================================
Average....................... 98%
----------------------------------------------------------------------------------------------------------------
(2) As shown in example 2, the primary and secondary standards are
not met at this monitoring site because the 3-year average of the
fourth-highest daily maximum 8-hour average ozone concentrations (i.e.,
0.093 ppm) is greater than 0.08 ppm. Note that the ozone concentration
data for 1994 is used in these computations, even though the data
capture is less than 75%, because the average fourth-highest daily
maximum 8-hour average concentration is greater than 0.08 ppm.
Example 2. Ambient Monitoring Site Failing to Meet the Primary and Secondary Ozone Standards
----------------------------------------------------------------------------------------------------------------
1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest
Percent Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
Year Valid Days hour Conc. hour Conc. hour Conc. hour Conc. hour Conc.
(ppm) (ppm) (ppm) (ppm) (ppm)
----------------------------------------------------------------------------------------------------------------
1993.............................. 96% 0.105 0.103 0.103 0.102 0.102
----------------------------------------------------------------------------------------------------------------
1994.............................. 74% 0.090 0.085 0.082 0.080 0.078
----------------------------------------------------------------------------------------------------------------
1995.............................. 98% 0.103 0.101 0.101 0.097 0.095
================================================================================================================
Average....................... 89%
----------------------------------------------------------------------------------------------------------------
3. Design Values for Primary and Secondary Ambient Air Quality
Standards for Ozone. The air quality design value at a monitoring site
is defined as that concentration that when reduced to the level of the
standard ensures that the site meets the standard. For a concentration-
based standard, the air quality design value is simply the standard-
related test statistic. Thus, for the primary and secondary ozone
standards, the 3-year average annual fourth-highest daily maximum 8-hour
average ozone concentration is also the air quality design value for the
site.
[62 FR 38895, July 18, 1997]
Appendix J to Part 50--Reference Method for the Determination of
Particulate Matter as PM10 in the Atmosphere
1.0 Applicability.
[[Page 65]]
1.1 This method provides for the measurement of the mass
concentration of particulate matter with an aerodynamic diameter less
than or equal to a nominal 10 micrometers (PM1O) in ambient
air over a 24-hour period for purposes of determining attainment and
maintenance of the primary and secondary national ambient air quality
standards for particulate matter specified in Sec. 50.6 of this
chapter. The measurement process is nondestructive, and the
PM10 sample can be subjected to subsequent physical or
chemical analyses. Quality assurance procedures and guidance are
provided in part 58, appendices A and B, of this chapter and in
References 1 and 2.
2.0 Principle.
2.1 An air sampler draws ambient air at a constant flow rate into a
specially shaped inlet where the suspended particulate matter is
inertially separated into one or more size fractions within the
PM10 size range. Each size fraction in the PM1O
size range is then collected on a separate filter over the specified
sampling period. The particle size discrimination characteristics
(sampling effectiveness and 50 percent cutpoint) of the sampler inlet
are prescribed as performance specifications in part 53 of this chapter.
2.2 Each filter is weighed (after moisture equilibration) before and
after use to determine the net weight (mass) gain due to collected
PM10. The total volume of air sampled, corrected to EPA
reference conditions (25 C, 101.3 kPa), is determined from the measured
flow rate and the sampling time. The mass concentration of
PM10 in the ambient air is computed as the total mass of
collected particles in the PM10 size range divided by the
volume of air sampled, and is expressed in micrograms per standard cubic
meter ([micro]g/std m\3\). For PM10 samples collected at
temperatures and pressures significantly different from EPA reference
conditions, these corrected concentrations sometimes differ
substantially from actual concentrations (in micrograms per actual cubic
meter), particularly at high elevations. Although not required, the
actual PM10 concentration can be calculated from the
corrected concentration, using the average ambient temperature and
barometric pressure during the sampling period.
2.3 A method based on this principle will be considered a reference
method only if (a) the associated sampler meets the requirements
specified in this appendix and the requirements in part 53 of this
chapter, and (b) the method has been designated as a reference method in
accordance with part 53 of this chapter.
3.0 Range.
3.1 The lower limit of the mass concentration range is determined by
the repeatability of filter tare weights, assuming the nominal air
sample volume for the sampler. For samplers having an automatic filter-
changing mechanism, there may be no upper limit. For samplers that do
not have an automatic filter-changing mechanism, the upper limit is
determined by the filter mass loading beyond which the sampler no longer
maintains the operating flow rate within specified limits due to
increased pressure drop across the loaded filter. This upper limit
cannot be specified precisely because it is a complex function of the
ambient particle size distribution and type, humidity, filter type, and
perhaps other factors. Nevertheless, all samplers should be capable of
measuring 24-hour PM10 mass concentrations of at least 300
[micro]g/std m\3\ while maintaining the operating flow rate within the
specified limits.
4.0 Precision.
4.1 The precision of PM10 samplers must be 5 [micro]g/
m\3\ for PM10 concentrations below 80 [micro]g/m\3\ and 7
percent for PM10 concentrations above 80 [micro]g/m\3\, as
required by part 53 of this chapter, which prescribes a test procedure
that determines the variation in the PM10 concentration
measurements of identical samplers under typical sampling conditions.
Continual assessment of precision via collocated samplers is required by
part 58 of this chapter for PM10 samplers used in certain
monitoring networks.
5.0 Accuracy.
5.1 Because the size of the particles making up ambient particulate
matter varies over a wide range and the concentration of particles
varies with particle size, it is difficult to define the absolute
accuracy of PM10 samplers. Part 53 of this chapter provides a
specification for the sampling effectiveness of PM10
samplers. This specification requires that the expected mass
concentration calculated for a candidate PM10 sampler, when
sampling a specified particle size distribution, be within 10 percent of that calculated for an ideal sampler whose
sampling effectiveness is explicitly specified. Also, the particle size
for 50 percent sampling effectivensss is required to be 10 0.5 micrometers. Other specifications related to
accuracy apply to flow measurement and calibration, filter media,
analytical (weighing) procedures, and artifact. The flow rate accuracy
of PM10 samplers used in certain monitoring networks is
required by part 58 of this chapter to be assessed periodically via flow
rate audits.
6.0 Potential Sources of Error.
6.1 Volatile Particles. Volatile particles collected on filters are
often lost during shipment and/or storage of the filters prior to the
post-sampling weighing \3\. Although shipment or storage of loaded
filters is sometimes unavoidable, filters should be reweighed as soon as
practical to minimize these losses.
6.2 Artifacts. Positive errors in PM10 concentration
measurements may result from retention of gaseous species on filters.
\4,5\ Such errors include the retention of sulfur
[[Page 66]]
dioxide and nitric acid. Retention of sulfur dioxide on filters,
followed by oxidation to sulfate, is referred to as artifact sulfate
formation, a phenomenon which increases with increasing filter
alkalinity. \6\ Little or no artifact sulfate formation should occur
using filters that meet the alkalinity specification in section 7.2.4.
Artifact nitrate formation, resulting primarily from retention of nitric
acid, occurs to varying degrees on many filter types, including glass
fiber, cellulose ester, and many quartz fiber filters. \5,7,8,9,10\ Loss
of true atmospheric particulate nitrate during or following sampling may
also occur due to dissociation or chemical reaction. This phenomenon has
been observed on Teflon[reg] filters \8\ and inferred for
quartz fiber filters. \11,12\ The magnitude of nitrate artifact errors
in PM10 mass concentration measurements will vary with
location and ambient temperature; however, for most sampling locations,
these errors are expected to be small.
6.3 Humidity. The effects of ambient humidity on the sample are
unavoidable. The filter equilibration procedure in section 9.0 is
designed to minimize the effects of moisture on the filter medium.
6.4 Filter Handling. Careful handling of filters between presampling
and postsampling weighings is necessary to avoid errors due to damaged
filters or loss of collected particles from the filters. Use of a filter
cartridge or cassette may reduce the magnitude of these errors. Filters
must also meet the integrity specification in section 7.2.3.
6.5 Flow Rate Variation. Variations in the sampler's operating flow
rate may alter the particle size discrimination characteristics of the
sampler inlet. The magnitude of this error will depend on the
sensitivity of the inlet to variations in flow rate and on the particle
distribution in the atmosphere during the sampling period. The use of a
flow control device (section 7.1.3) is required to minimize this error.
6.6 Air Volume Determination. Errors in the air volume determination
may result from errors in the flow rate and/or sampling time
measurements. The flow control device serves to minimize errors in the
flow rate determination, and an elapsed time meter (section 7.1.5) is
required to minimize the error in the sampling time measurement.
7.0 Apparatus.
7.1 PM10 Sampler.
7.1.1 The sampler shall be designed to:
a. Draw the air sample into the sampler inlet and through the
particle collection filter at a uniform face velocity.
b. Hold and seal the filter in a horizontal position so that sample
air is drawn downward through the filter.
c. Allow the filter to be installed and removed conveniently.
d. Protect the filter and sampler from precipitation and prevent
insects and other debris from being sampled.
e. Minimize air leaks that would cause error in the measurement of
the air volume passing through the filter.
f. Discharge exhaust air at a sufficient distance from the sampler
inlet to minimize the sampling of exhaust air.
g. Minimize the collection of dust from the supporting surface.
7.1.2 The sampler shall have a sample air inlet system that, when
operated within a specified flow rate range, provides particle size
discrimination characteristics meeting all of the applicable performance
specifications prescribed in part 53 of this chapter. The sampler inlet
shall show no significant wind direction dependence. The latter
requirement can generally be satisfied by an inlet shape that is
circularly symmetrical about a vertical axis.
7.1.3 The sampler shall have a flow control device capable of
maintaining the sampler's operating flow rate within the flow rate
limits specified for the sampler inlet over normal variations in line
voltage and filter pressure drop.
7.1.4 The sampler shall provide a means to measure the total flow
rate during the sampling period. A continuous flow recorder is
recommended but not required. The flow measurement device shall be
accurate to 2 percent.
7.1.5 A timing/control device capable of starting and stopping the
sampler shall be used to obtain a sample collection period of 24 1 hr (1,440 60 min). An elapsed
time meter, accurate to within 15 minutes, shall
be used to measure sampling time. This meter is optional for samplers
with continuous flow recorders if the sampling time measurement obtained
by means of the recorder meets the 15 minute
accuracy specification.
7.1.6 The sampler shall have an associated operation or instruction
manual as required by part 53 of this chapter which includes detailed
instructions on the calibration, operation, and maintenance of the
sampler.
7.2 Filters.
7.2.1 Filter Medium. No commercially available filter medium is
ideal in all respects for all samplers. The user's goals in sampling
determine the relative importance of various filter characteristics
(e.g., cost, ease of handling, physical and chemical characteristics,
etc.) and, consequently, determine the choice among acceptable filters.
Furthermore, certain types of filters may not be suitable for use with
some samplers, particularly under heavy loading conditions (high mass
concentrations), because of high or rapid increase in the filter flow
resistance that would exceed the capability of the sampler's flow
control device. However, samplers equipped with automatic filter-
changing
[[Page 67]]
mechanisms may allow use of these types of filters. The specifications
given below are minimum requirements to ensure acceptability of the
filter medium for measurement of PM10 mass concentrations.
Other filter evaluation criteria should be considered to meet individual
sampling and analysis objectives.
7.2.2 Collection Efficiency. =99 percent, as measured by
the DOP test (ASTM-2986) with 0.3 [micro]m particles at the sampler's
operating face velocity.
7.2.3 Integrity. 5 [micro]g/m\3\ (assuming
sampler's nominal 24-hour air sample volume). Integrity is measured as
the PM10 concentration equivalent corresponding to the
average difference between the initial and the final weights of a random
sample of test filters that are weighed and handled under actual or
simulated sampling conditions, but have no air sample passed through
them (i.e., filter blanks). As a minimum, the test procedure must
include initial equilibration and weighing, installation on an
inoperative sampler, removal from the sampler, and final equilibration
and weighing.
7.2.4 Alkalinity. <25 microequivalents/gram of filter, as measured
by the procedure given in Reference 13 following at least two months
storage in a clean environment (free from contamination by acidic gases)
at room temperature and humidity.
7.3 Flow Rate Transfer Standard. The flow rate transfer standard
must be suitable for the sampler's operating flow rate and must be
calibrated against a primary flow or volume standard that is traceable
to the National Bureau of Standards (NBS). The flow rate transfer
standard must be capable of measuring the sampler's operating flow rate
with an accuracy of 2 percent.
7.4 Filter Conditioning Environment.
7.4.1 Temperature range: 15 to 30 C.
7.4.2 Temperature control: 3 C.
7.4.3 Humidity range: 20% to 45% RH.
7.4.4 Humidity control: 5% RH.
7.5 Analytical Balance. The analytical balance must be suitable for
weighing the type and size of filters required by the sampler. The range
and sensitivity required will depend on the filter tare weights and mass
loadings. Typically, an analytical balance with a sensitivity of 0.1 mg
is required for high volume samplers (flow rates 0.5 m\3\/
min). Lower volume samplers (flow rates <0.5 m\3\/min) will require a
more sensitive balance.
8.0 Calibration.
8.1 General Requirements.
8.1.1 Calibration of the sampler's flow measurement device is
required to establish traceability of subsequent flow measurements to a
primary standard. A flow rate transfer standard calibrated against a
primary flow or volume standard shall be used to calibrate or verify the
accuracy of the sampler's flow measurement device.
8.1.2 Particle size discrimination by inertial separation requires
that specific air velocities be maintained in the sampler's air inlet
system. Therefore, the flow rate through the sampler's inlet must be
maintained throughout the sampling period within the design flow rate
range specified by the manufacturer. Design flow rates are specified as
actual volumetric flow rates, measured at existing conditions of
temperature and pressure (Qa). In contrast, mass
concentrations of PM10 are computed using flow rates
corrected to EPA reference conditions of temperature and pressure
(Qstd).
8.2 Flow Rate Calibration Procedure.
8.2.1 PM10 samplers employ various types of flow control
and flow measurement devices. The specific procedure used for flow rate
calibration or verification will vary depending on the type of flow
controller and flow indicator employed. Calibration in terms of actual
volumetric flow rates (Qa) is generally recommended, but
other measures of flow rate (e.g., Qstd) may be used provided
the requirements of section 8.1 are met. The general procedure given
here is based on actual volumetric flow units (Qa) and serves
to illustrate the steps involved in the calibration of a PM10
sampler. Consult the sampler manufacturer's instruction manual and
Reference 2 for specific guidance on calibration. Reference 14 provides
additional information on the use of the commonly used measures of flow
rate and their interrelationships.
8.2.2 Calibrate the flow rate transfer standard against a primary
flow or volume standard traceable to NBS. Establish a calibration
relationship (e.g., an equation or family of curves) such that
traceability to the primary standard is accurate to within 2 percent
over the expected range of ambient conditions (i.e., temperatures and
pressures) under which the transfer standard will be used. Recalibrate
the transfer standard periodically.
8.2.3 Following the sampler manufacturer's instruction manual,
remove the sampler inlet and connect the flow rate transfer standard to
the sampler such that the transfer standard accurately measures the
sampler's flow rate. Make sure there are no leaks between the transfer
standard and the sampler.
8.2.4 Choose a minimum of three flow rates (actual m\3\/min), spaced
over the acceptable flow rate range specified for the inlet (see 7.1.2)
that can be obtained by suitable adjustment of the sampler flow rate. In
accordance with the sampler manufacturer's instruction manual, obtain or
verify the calibration relationship between the flow rate (actual m\3\/
min) as indicated by the transfer standard and the sampler's flow
indicator response. Record the ambient temperature and barometric
pressure. Temperature and pressure corrections to subsequent flow
indicator readings may be required for certain types of
[[Page 68]]
flow measurement devices. When such corrections are necessary,
correction on an individual or daily basis is preferable. However,
seasonal average temperature and average barometric pressure for the
sampling site may be incorporated into the sampler calibration to avoid
daily corrections. Consult the sampler manufacturer's instruction manual
and Reference 2 for additional guidance.
8.2.5 Following calibration, verify that the sampler is operating at
its design flow rate (actual m\3\/min) with a clean filter in place.
8.2.6 Replace the sampler inlet.
9.0 Procedure.
9.1 The sampler shall be operated in accordance with the specific
guidance provided in the sampler manufacturer's instruction manual and
in Reference 2. The general procedure given here assumes that the
sampler's flow rate calibration is based on flow rates at ambient
conditions (Qa) and serves to illustrate the steps involved
in the operation of a PM10 sampler.
9.2 Inspect each filter for pinholes, particles, and other
imperfections. Establish a filter information record and assign an
identification number to each filter.
9.3 Equilibrate each filter in the conditioning environment (see
7.4) for at least 24 hours.
9.4 Following equilibration, weigh each filter and record the
presampling weight with the filter identification number.
9.5 Install a preweighed filter in the sampler following the
instructions provided in the sampler manufacturer's instruction manual.
9.6 Turn on the sampler and allow it to establish run-temperature
conditions. Record the flow indicator reading and, if needed, the
ambient temperature and barometric pressure. Determine the sampler flow
rate (actual m\3\/min) in accordance with the instructions provided in
the sampler manufacturer's instruction manual. NOTE.--No onsite
temperature or pressure measurements are necessary if the sampler's flow
indicator does not require temperature or pressure corrections or if
seasonal average temperature and average barometric pressure for the
sampling site are incorporated into the sampler calibration (see step
8.2.4). If individual or daily temperature and pressure corrections are
required, ambient temperature and barometric pressure can be obtained by
on-site measurements or from a nearby weather station. Barometric
pressure readings obtained from airports must be station pressure, not
corrected to sea level, and may need to be corrected for differences in
elevation between the sampling site and the airport.
9.7 If the flow rate is outside the acceptable range specified by
the manufacturer, check for leaks, and if necessary, adjust the flow
rate to the specified setpoint. Stop the sampler.
9.8 Set the timer to start and stop the sampler at appropriate
times. Set the elapsed time meter to zero or record the initial meter
reading.
9.9 Record the sample information (site location or identification
number, sample date, filter identification number, and sampler model and
serial number).
9.10 Sample for 24 1 hours.
9.11 Determine and record the average flow rate (Qa) in
actual m\3\/min for the sampling period in accordance with the
instructions provided in the sampler manufacturer's instruction manual.
Record the elapsed time meter final reading and, if needed, the average
ambient temperature and barometric pressure for the sampling period (see
note following step 9.6).
9.12 Carefully remove the filter from the sampler, following the
sampler manufacturer's instruction manual. Touch only the outer edges of
the filter.
9.13 Place the filter in a protective holder or container (e.g.,
petri dish, glassine envelope, or manila folder).
9.14 Record any factors such as meteorological conditions,
construction activity, fires or dust storms, etc., that might be
pertinent to the measurement on the filter information record.
9.15 Transport the exposed sample filter to the filter conditioning
environment as soon as possible for equilibration and subsequent
weighing.
9.16 Equilibrate the exposed filter in the conditioning environment
for at least 24 hours under the same temperature and humidity conditions
used for presampling filter equilibration (see 9.3).
9.17 Immediately after equilibration, reweigh the filter and record
the postsampling weight with the filter identification number.
10.0 Sampler Maintenance.
10.1 The PM10 sampler shall be maintained in strict
accordance with the maintenance procedures specified in the sampler
manufacturer's instruction manual.
11.0 Calculations.
11.1 Calculate the average flow rate over the sampling period
corrected to EPA reference conditions as Qstd. When the
sampler's flow indicator is calibrated in actual volumetric units
(Qa), Qstd is calculated as:
Qstd=Qax(Pav/
Tav)(Tstd/Pstd)
where
Qstd = average flow rate at EPA reference conditions, std
m\3\/min;
Qa = average flow rate at ambient conditions, m\3\/min;
Pav = average barometric pressure during the sampling period
or average barometric pressure for the sampling site, kPa (or mm Hg);
Tav = average ambient temperature during the sampling period
or seasonal average
[[Page 69]]
ambient temperature for the sampling site, K;
Tstd = standard temperature, defined as 298 K;
Pstd = standard pressure, defined as 101.3 kPa (or 760 mm
Hg).
11.2 Calculate the total volume of air sampled as:
Vstd = Qstdxt
where
Vstd = total air sampled in standard volume units, std m\3\;
t = sampling time, min.
11.3 Calculate the PM10 concentration as:
PM10 = (Wf-Wi)x10\6\/Vstd
where
PM10 = mass concentration of PM10, [micro]g/std
m\3\;
Wf, Wi = final and initial weights of filter
collecting PM1O particles, g;
10\6\ = conversion of g to [micro]g.
Note: If more than one size fraction in the PM10 size
range is collected by the sampler, the sum of the net weight gain by
each collection filter [[Sigma](Wf-Wi)] is used to
calculate the PM10 mass concentration.
12.0 References.
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume I, Principles. EPA-600/9-76-005, March 1976. Available from CERI,
ORD Publications, U.S. Environmental Protection Agency, 26 West St.
Clair Street, Cincinnati, OH 45268.
2. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume II, Ambient Air Specific Methods. EPA-600/4-77-027a, May 1977.
Available from CERI, ORD Publications, U.S. Environmental Protection
Agency, 26 West St. Clair Street, Cincinnati, OH 45268.
3. Clement, R.E., and F.W. Karasek. Sample Composition Changes in
Sampling and Analysis of Organic Compounds in Aerosols. Int. J. Environ.
Analyt. Chem., 7:109, 1979.
4. Lee, R.E., Jr., and J. Wagman. A Sampling Anomaly in the
Determination of Atmospheric Sulfate Concentration. Amer. Ind. Hyg.
Assoc. J., 27:266, 1966.
5. Appel, B.R., S.M. Wall, Y. Tokiwa, and M. Haik. Interference
Effects in Sampling Particulate Nitrate in Ambient Air. Atmos. Environ.,
13:319, 1979.
6. Coutant, R.W. Effect of Environmental Variables on Collection of
Atmospheric Sulfate. Environ. Sci. Technol., 11:873, 1977.
7. Spicer, C.W., and P. Schumacher. Interference in Sampling
Atmospheric Particulate Nitrate. Atmos. Environ., 11:873, 1977.
8. Appel, B.R., Y. Tokiwa, and M. Haik. Sampling of Nitrates in
Ambient Air. Atmos. Environ., 15:283, 1981.
9. Spicer, C.W., and P.M. Schumacher. Particulate Nitrate:
Laboratory and Field Studies of Major Sampling Interferences. Atmos.
Environ., 13:543, 1979.
10. Appel, B.R. Letter to Larry Purdue, U.S. EPA, Environmental
Monitoring and Support Laboratory. March 18, 1982, Docket No. A-82-37,
II-I-1.
11. Pierson, W.R., W.W. Brachaczek, T.J. Korniski, T.J. Truex, and
J.W. Butler. Artifact Formation of Sulfate, Nitrate, and Hydrogen Ion on
Backup Filters: Allegheny Mountain Experiment. J. Air Pollut. Control
Assoc., 30:30, 1980.
12. Dunwoody, C.L. Rapid Nitrate Loss From PM10 Filters.
J. Air Pollut. Control Assoc., 36:817, 1986.
13. Harrell, R.M. Measuring the Alkalinity of Hi-Vol Air Filters.
EMSL/RTP-SOP-QAD-534, October 1985. Available from the U.S.
Environmental Protection Agency, EMSL/QAD, Research Triangle Park, NC
27711.
14. Smith, F., P.S. Wohlschlegel, R.S.C. Rogers, and D.J. Mulligan.
Investigation of Flow Rate Calibration Procedures Associated With the
High Volume Method for Determination of Suspended Particulates. EPA-600/
4-78-047, U.S. Environmental Protection Agency, Research Triangle Park,
NC 27711, 1978.
[52 FR 24664, July 1, 1987; 52 FR 29467, Aug. 7, 1987]
Appendix K to Part 50--Interpretation of the National Ambient Air
Quality Standards for PM10
1.0 General.
(a) This appendix explains the computations necessary for analyzing
particulate matter data to determine attainment of the 24-hour and
annual standards specified in 40 CFR 50.6. For the primary and secondary
standards, particulate matter is measured in the ambient air as
PM10 (particles with an aerodynamic diameter less than or
equal to a nominal 10 micrometers) by a reference method based on
appendix J of this part and designated in accordance with part 53 of
this chapter, or by an equivalent method designated in accordance with
part 53 of this chapter. The required frequency of measurements is
specified in part 58 of this chapter.
(b) The terms used in this appendix are defined as follows:
Average refers to an arithmetic mean. All particulate matter
standards are expressed in terms of expected annual values: Expected
number of exceedances per year for the 24-hour standards and expected
annual arithmetic mean for the annual standards.
Daily value for PM10 refers to the 24-hour average
concentration of PM10 calculated or measured from midnight to
midnight (local time).
Exceedance means a daily value that is above the level of the 24-
hour standard after
[[Page 70]]
rounding to the nearest 10 [micro]g/m\3\ (i.e., values ending in 5 or
greater are to be rounded up).
Expected annual value is the number approached when the annual
values from an increasing number of years are averaged, in the absence
of long-term trends in emissions or meteorological conditions.
Year refers to a calendar year.
(c) Although the discussion in this appendix focuses on monitored
data, the same principles apply to modeling data, subject to EPA
modeling guidelines.
2.0 Attainment Determinations.
2.1 24-Hour Primary and Secondary Standards.
(a) Under 40 CFR 50.6(a) the 24-hour primary and secondary standards
are attained when the expected number of exceedances per year at each
monitoring site is less than or equal to one. In the simplest case, the
number of expected exceedances at a site is determined by recording the
number of exceedances in each calendar year and then averaging them over
the past 3 calendar years. Situations in which 3 years of data are not
available and possible adjustments for unusual events or trends are
discussed in sections 2.3 and 2.4 of this appendix. Further, when data
for a year are incomplete, it is necessary to compute an estimated
number of exceedances for that year by adjusting the observed number of
exceedances. This procedure, performed by calendar quarter, is described
in section 3.0 of this appendix. The expected number of exceedances is
then estimated by averaging the individual annual estimates for the past
3 years.
(b) The comparison with the allowable expected exceedance rate of
one per year is made in terms of a number rounded to the nearest tenth
(fractional values equal to or greater than 0.05 are to be rounded up;
e.g., an exceedance rate of 1.05 would be rounded to 1.1, which is the
lowest rate for nonattainment).
2.2 Annual Primary and Secondary Standards. Under 40 CFR 50.6(b),
the annual primary and secondary standards are attained when the
expected annual arithmetic mean PM10 concentration is less
than or equal to the level of the standard. In the simplest case, the
expected annual arithmetic mean is determined by averaging the annual
arithmetic mean PM10 concentrations for the past 3 calendar
years. Because of the potential for incomplete data and the possible
seasonality in PM10 concentrations, the annual mean shall be
calculated by averaging the four quarterly means of PM10
concentrations within the calendar year. The equations for calculating
the annual arithmetic mean are given in section 4.0 of this appendix.
Situations in which 3 years of data are not available and possible
adjustments for unusual events or trends are discussed in sections 2.3
and 2.4 of this appendix. The expected annual arithmetic mean is rounded
to the nearest 1 [micro]g/m\3\ before comparison with the annual
standards (fractional values equal to or greater than 0.5 are to be
rounded up).
2.3 Data Requirements.
(a) 40 CFR 58.13 specifies the required minimum frequency of
sampling for PM10. For the purposes of making comparisons
with the particulate matter standards, all data produced by National Air
Monitoring Stations (NAMS), State and Local Air Monitoring Stations
(SLAMS) and other sites submitted to EPA in accordance with the part 58
requirements must be used, and a minimum of 75 percent of the scheduled
PM10 samples per quarter are required.
(b) To demonstrate attainment of either the annual or 24-hour
standards at a monitoring site, the monitor must provide sufficient data
to perform the required calculations of sections 3.0 and 4.0 of this
appendix. The amount of data required varies with the sampling
frequency, data capture rate and the number of years of record. In all
cases, 3 years of representative monitoring data that meet the 75
percent criterion of the previous paragraph should be utilized, if
available, and would suffice. More than 3 years may be considered, if
all additional representative years of data meeting the 75 percent
criterion are utilized. Data not meeting these criteria may also suffice
to show attainment; however, such exceptions will have to be approved by
the appropriate Regional Administrator in accordance with EPA guidance.
(c) There are less stringent data requirements for showing that a
monitor has failed an attainment test and thus has recorded a violation
of the particulate matter standards. Although it is generally necessary
to meet the minimum 75 percent data capture requirement per quarter to
use the computational equations described in sections 3.0 and 4.0 of
this appendix, this criterion does not apply when less data is
sufficient to unambiguously establish nonattainment. The following
examples illustrate how nonattainment can be demonstrated when a site
fails to meet the completeness criteria. Nonattainment of the 24-hour
primary standards can be established by the observed annual number of
exceedances (e.g., four observed exceedances in a single year), or by
the estimated number of exceedances derived from the observed number of
exceedances and the required number of scheduled samples (e.g., two
observed exceedances with every other day sampling). Nonattainment of
the annual standards can be demonstrated on the basis of quarterly mean
concentrations developed from observed data combined with one-half the
minimum detectable concentration substituted for missing values. In both
cases, expected annual values must exceed the levels allowed by the
standards.
2.4 Adjustment for Exceptional Events and Trends.
[[Page 71]]
(a) An exceptional event is an uncontrollable event caused by
natural sources of particulate matter or an event that is not expected
to recur at a given location. Inclusion of such a value in the
computation of exceedances or averages could result in inappropriate
estimates of their respective expected annual values. To reduce the
effect of unusual events, more than 3 years of representative data may
be used. Alternatively, other techniques, such as the use of statistical
models or the use of historical data could be considered so that the
event may be discounted or weighted according to the likelihood that it
will recur. The use of such techniques is subject to the approval of the
appropriate Regional Administrator in accordance with EPA guidance.
(b) In cases where long-term trends in emissions and air quality are
evident, mathematical techniques should be applied to account for the
trends to ensure that the expected annual values are not inappropriately
biased by unrepresentative data. In the simplest case, if 3 years of
data are available under stable emission conditions, this data should be
used. In the event of a trend or shift in emission patterns, either the
most recent representative year(s) could be used or statistical
techniques or models could be used in conjunction with previous years of
data to adjust for trends. The use of less than 3 years of data, and any
adjustments are subject to the approval of the appropriate Regional
Administrator in accordance with EPA guidance.
3.0 Computational Equations for the 24-hour Standards.
3.1 Estimating Exceedances for a Year.
(a) If PM10 sampling is scheduled less frequently than
every day, or if some scheduled samples are missed, a PM10
value will not be available for each day of the year. To account for the
possible effect of incomplete data, an adjustment must be made to the
data collected at each monitoring location to estimate the number of
exceedances in a calendar year. In this adjustment, the assumption is
made that the fraction of missing values that would have exceeded the
standard level is identical to the fraction of measured values above
this level. This computation is to be made for all sites that are
scheduled to monitor throughout the entire year and meet the minimum
data requirements of section 2.3 of this appendix. Because of possible
seasonal imbalance, this adjustment shall be applied on a quarterly
basis. The estimate of the expected number of exceedances for the
quarter is equal to the observed number of exceedances plus an increment
associated with the missing data. The following equation must be used
for these computations:
Equation 1
[GRAPHIC] [TIFF OMITTED] TR18JY97.180
where:
eq = the estimated number of exceedances for calendar quarter
q;
vq = the observed number of exceedances for calendar quarter
q;
Nq = the number of days in calendar quarter q;
nq = the number of days in calendar quarter q with
PM10 data; and
q = the index for calendar quarter, q=1, 2, 3 or 4.
(b) The estimated number of exceedances for a calendar quarter must
be rounded to the nearest hundredth (fractional values equal to or
greater than 0.005 must be rounded up).
(c) The estimated number of exceedances for the year, e, is the sum
of the estimates for each calendar quarter.
Equation 2
[GRAPHIC] [TIFF OMITTED] TR18JY97.181
(d) The estimated number of exceedances for a single year must be
rounded to one decimal place (fractional values equal to or greater than
0.05 are to be rounded up). The expected number of exceedances is then
estimated by averaging the individual annual estimates for the most
recent 3 or more representative years of data. The expected number of
exceedances must be rounded to one decimal place (fractional values
equal to or greater than 0.05 are to be rounded up).
(e) The adjustment for incomplete data will not be necessary for
monitoring or modeling data which constitutes a complete record, i.e.,
365 days per year.
(f) To reduce the potential for overestimating the number of
expected exceedances, the correction for missing data will not be
required for a calendar quarter in which the first observed exceedance
has occurred if:
(1) There was only one exceedance in the calendar quarter;
(2) Everyday sampling is subsequently initiated and maintained for 4
calendar quarters in accordance with 40 CFR 58.13; and
(3) Data capture of 75 percent is achieved during the required
period of everyday sampling. In addition, if the first exceedance is
observed in a calendar quarter in which the monitor is already sampling
every day, no adjustment for missing data will be made to the first
exceedance if a 75 percent data capture rate was achieved in the quarter
in which it was observed.
[[Page 72]]
Example 1
a. During a particular calendar quarter, 39 out of a possible 92
samples were recorded, with one observed exceedance of the 24-hour
standard. Using Equation 1, the estimated number of exceedances for the
quarter is:
eq=1x92/39=2.359 or 2.36.
b. If the estimated exceedances for the other 3 calendar quarters in
the year were 2.30, 0.0 and 0.0, then, using Equation 2, the estimated
number of exceedances for the year is 2.36=2.30=0.0=0.0 which equals
4.66 or 4.7. If no exceedances were observed for the 2 previous years,
then the expected number of exceedances is estimated by: (1/
3)x(4.7=0=0)=1.57 or 1.6. Since 1.6 exceeds the allowable number of
expected exceedances, this monitoring site would fail the attainment
test.
Example 2
In this example, everyday sampling was initiated following the first
observed exceedance as required by 40 CFR 58.13. Accordingly, the first
observed exceedance would not be adjusted for incomplete sampling.
During the next three quarters, 1.2 exceedances were estimated. In this
case, the estimated exceedances for the year would be 1.0=1.2=0.0=0.0
which equals 2.2. If, as before, no exceedances were observed for the
two previous years, then the estimated exceedances for the 3-year period
would then be (1/3)x(2.2=0.0=0.0)=0.7, and the monitoring site would not
fail the attainment test.
3.2 Adjustments for Non-Scheduled Sampling Days.
(a) If a systematic sampling schedule is used and sampling is
performed on days in addition to the days specified by the systematic
sampling schedule, e.g., during episodes of high pollution, then an
adjustment must be made in the eqution for the estimation of
exceedances. Such an adjustment is needed to eliminate the bias in the
estimate of the quarterly and annual number of exceedances that would
occur if the chance of an exceedance is different for scheduled than for
non-scheduled days, as would be the case with episode sampling.
(b) The required adjustment treats the systematic sampling schedule
as a stratified sampling plan. If the period from one scheduled sample
until the day preceding the next scheduled sample is defined as a
sampling stratum, then there is one stratum for each scheduled sampling
day. An average number of observed exceedances is computed for each of
these sampling strata. With nonscheduled sampling days, the estimated
number of exceedances is defined as:
Equation 3
[GRAPHIC] [TIFF OMITTED] TR18JY97.182
where:
eq = the estimated number of exceedances for the quarter;
Nq = the number of days in the quarter;
mq = the number of strata with samples during the quarter;
vj = the number of observed exceedances in stratum j; and
kj = the number of actual samples in stratum j.
(c) Note that if only one sample value is recorded in each stratum,
then Equation 3 reduces to Equation 1.
Example 3
A monitoring site samples according to a systematic sampling
schedule of one sample every 6 days, for a total of 15 scheduled samples
in a quarter out of a total of 92 possible samples. During one 6-day
period, potential episode levels of PM10 were suspected, so 5
additional samples were taken. One of the regular scheduled samples was
missed, so a total of 19 samples in 14 sampling strata were measured.
The one 6-day sampling stratum with 6 samples recorded 2 exceedances.
The remainder of the quarter with one sample per stratum recorded zero
exceedances. Using Equation 3, the estimated number of exceedances for
the quarter is:
eq=(92/14)x(2/6=0=. . .=0)=2.19.
4.0 Computational Equations for Annual Standards.
4.1 Calculation of the Annual Arithmetic Mean. (a) An annual
arithmetic mean value for PM10 is determined by averaging the
quarterly means for the 4 calendar quarters of the year. The following
equation is to be used for calculation of the mean for a calendar
quarter:
Equation 4
[GRAPHIC] [TIFF OMITTED] TR18JY97.183
where:
xq = the quarterly mean concentration for quarter q, q=1, 2,
3, or 4,
nq = the number of samples in the quarter, and
xi = the ith concentration value recorded in the quarter.
(b) The quarterly mean, expressed in [micro]g/m\3\, must be rounded
to the nearest tenth (fractional values of 0.05 should be rounded up).
[[Page 73]]
(c) The annual mean is calculated by using the following equation:
Equation 5
[GRAPHIC] [TIFF OMITTED] TR18JY97.184
where:
x = the annual mean; and
xq = the mean for calendar quarter q.
(d) The average of quarterly means must be rounded to the nearest
tenth (fractional values of 0.05 should be rounded up).
(e) The use of quarterly averages to compute the annual average will
not be necessary for monitoring or modeling data which results in a
complete record, i.e., 365 days per year.
(f) The expected annual mean is estimated as the average of three or
more annual means. This multi-year estimate, expressed in [micro]g/m\3\,
shall be rounded to the nearest integer for comparison with the annual
standard (fractional values of 0.5 should be rounded up).
Example 4
Using Equation 4, the quarterly means are calculated for each
calendar quarter. If the quarterly means are 52.4, 75.3, 82.1, and 63.2
[micro]g/m\3\, then the annual mean is:
x = (1/4)x(52.4=75.3=82.1=63.2) = 68.25 or 68.3.
4.2 Adjustments for Non-scheduled Sampling Days. (a) An adjustment
in the calculation of the annual mean is needed if sampling is performed
on days in addition to the days specified by the systematic sampling
schedule. For the same reasons given in the discussion of estimated
exceedances, under section 3.2 of this appendix, the quarterly averages
would be calculated by using the following equation:
Equation 6
[GRAPHIC] [TIFF OMITTED] TR18JY97.185
where:
xq = the quarterly mean concentration for quarter q, q=1, 2,
3, or 4;
xij = the ith concentration value recorded in stratum j;
kj = the number of actual samples in stratum j; and
mq = the number of strata with data in the quarter.
(b) If one sample value is recorded in each stratum, Equation 6
reduces to a simple arithmetic average of the observed values as
described by Equation 4.
Example 5
a. During one calendar quarter, 9 observations were recorded. These
samples were distributed among 7 sampling strata, with 3 observations in
one stratum. The concentrations of the 3 observations in the single
stratum were 202, 242, and 180 [micro]g/m\3\. The remaining 6 observed
concentrations were 55, 68, 73, 92, 120, and 155 [micro]g/m\3\. Applying
the weighting factors specified in Equation 6, the quarterly mean is:
xq = (1/7) x [(1/3) x (202 = 242 = 180) = 155 = 68 = 73 = 92
= 120 = 155] = 110.1
b. Although 24-hour measurements are rounded to the nearest 10
[micro]g/m\3\ for determinations of exceedances of the 24-hour standard,
note that these values are rounded to the nearest 1 [micro]g/m\3\ for
the calculation of means.
[62 FR 38712, July 18, 1997]
Appendix L to Part 50--Reference Method for the Determination of Fine
Particulate Matter as PM2.5 in the Atmosphere
1.0 Applicability.
1.1 This method provides for the measurement of the mass
concentration of fine particulate matter having an aerodynamic diameter
less than or equal to a nominal 2.5 micrometers (PM2.5) in
ambient air over a 24-hour period for purposes of determining whether
the primary and secondary national ambient air quality standards for
fine particulate matter specified in Sec. 50.7 of this part are met.
The measurement process is considered to be nondestructive, and the
PM2.5 sample obtained can be subjected to subsequent physical
or chemical analyses. Quality assessment procedures are provided in part
58, appendix A of this chapter, and quality assurance guidance are
provided in references 1, 2, and 3 in section 13.0 of this appendix.
1.2 This method will be considered a reference method for purposes
of part 58 of this chapter only if:
(a) The associated sampler meets the requirements specified in this
appendix and the applicable requirements in part 53 of this chapter, and
(b) The method and associated sampler have been designated as a
reference method in accordance with part 53 of this chapter.
1.3 PM2.5 samplers that meet nearly all specifications
set forth in this method but have minor deviations and/or modifications
of the reference method sampler will be designated as ``Class I''
equivalent methods for PM2.5 in accordance with part 53 of
this chapter.
2.0 Principle.
2.1 An electrically powered air sampler draws ambient air at a
constant volumetric flow rate into a specially shaped inlet and
[[Page 74]]
through an inertial particle size separator (impactor) where the
suspended particulate matter in the PM2.5 size range is
separated for collection on a polytetrafluoroethylene (PTFE) filter over
the specified sampling period. The air sampler and other aspects of this
reference method are specified either explicitly in this appendix or
generally with reference to other applicable regulations or quality
assurance guidance.
2.2 Each filter is weighed (after moisture and temperature
conditioning) before and after sample collection to determine the net
gain due to collected PM2.5. The total volume of air sampled
is determined by the sampler from the measured flow rate at actual
ambient temperature and pressure and the sampling time. The mass
concentration of PM2.5 in the ambient air is computed as the
total mass of collected particles in the PM2.5 size range
divided by the actual volume of air sampled, and is expressed in
micrograms per cubic meter of air ([micro]g/m\3\).
3.0 PM2.5 Measurement Range.
3.1 Lower concentration limit. The lower detection limit of the mass
concentration measurement range is estimated to be approximately 2
[micro]g/m\3\, based on noted mass changes in field blanks in
conjunction with the 24 m\3\ nominal total air sample volume specified
for the 24-hour sample.
3.2 Upper concentration limit. The upper limit of the mass
concentration range is determined by the filter mass loading beyond
which the sampler can no longer maintain the operating flow rate within
specified limits due to increased pressure drop across the loaded
filter. This upper limit cannot be specified precisely because it is a
complex function of the ambient particle size distribution and type,
humidity, the individual filter used, the capacity of the sampler flow
rate control system, and perhaps other factors. Nevertheless, all
samplers are estimated to be capable of measuring 24-hour
PM2.5 mass concentrations of at least 200 [micro]g/m\3\ while
maintaining the operating flow rate within the specified limits.
3.3 Sample period. The required sample period for PM2.5
concentration measurements by this method shall be 1,380 to 1500 minutes
(23 to 25 hours). However, when a sample period is less than 1,380
minutes, the measured concentration (as determined by the collected
PM2.5 mass divided by the actual sampled air volume),
multiplied by the actual number of minutes in the sample period and
divided by 1,440, may be used as if it were a valid concentration
measurement for the specific purpose of determining a violation of the
NAAQS. This value assumes that the PM2.5 concentration is
zero for the remaining portion of the sample period and therefore
represents the minimum concentration that could have been measured for
the full 24-hour sample period. Accordingly, if the value thus
calculated is high enough to be an exceedance, such an exceedance would
be a valid exceedance for the sample period. When reported to AIRS, this
data value should receive a special code to identify it as not to be
commingled with normal concentration measurements or used for other
purposes.
4.0 Accuracy.
4.1 Because the size and volatility of the particles making up
ambient particulate matter vary over a wide range and the mass
concentration of particles varies with particle size, it is difficult to
define the accuracy of PM2.5 measurements in an absolute
sense. The accuracy of PM2.5 measurements is therefore
defined in a relative sense, referenced to measurements provided by this
reference method. Accordingly, accuracy shall be defined as the degree
of agreement between a subject field PM2.5 sampler and a
collocated PM2.5 reference method audit sampler operating
simultaneously at the monitoring site location of the subject sampler
and includes both random (precision) and systematic (bias) errors. The
requirements for this field sampler audit procedure are set forth in
part 58, appendix A of this chapter.
4.2 Measurement system bias. Results of collocated measurements
where the duplicate sampler is a reference method sampler are used to
assess a portion of the measurement system bias according to the
schedule and procedure specified in part 58, appendix A of this chapter.
4.3 Audits with reference method samplers to determine system
accuracy and bias. According to the schedule and procedure specified in
part 58, appendix A of this chapter, a reference method sampler is
required to be located at each of selected PM2.5 SLAMS sites
as a duplicate sampler. The results from the primary sampler and the
duplicate reference method sampler are used to calculate accuracy of the
primary sampler on a quarterly basis, bias of the primary sampler on an
annual basis, and bias of a single reporting organization on an annual
basis. Reference 2 in section 13.0 of this appendix provides additional
information and guidance on these reference method audits.
4.4 Flow rate accuracy and bias. Part 58, appendix A of this chapter
requires that the flow rate accuracy and bias of individual
PM2.5 samplers used in SLAMS monitoring networks be assessed
periodically via audits of each sampler's operational flow rate. In
addition, part 58, appendix A of this chapter requires that flow rate
bias for each reference and equivalent method operated by each reporting
organization be assessed quarterly and annually. Reference 2 in section
13.0 of this appendix provides additional information and guidance on
flow rate accuracy audits and calculations for accuracy and bias.
5.0 Precision. A data quality objective of 10 percent coefficient of
variation or better has
[[Page 75]]
been established for the operational precision of PM2.5
monitoring data.
5.1 Tests to establish initial operational precision for each
reference method sampler are specified as a part of the requirements for
designation as a reference method under Sec. 53.58 of this chapter.
5.2 Measurement System Precision. Collocated sampler results, where
the duplicate sampler is not a reference method sampler but is a sampler
of the same designated method as the primary sampler, are used to assess
measurement system precision according to the schedule and procedure
specified in part 58, appendix A of this chapter. Part 58, appendix A of
this chapter requires that these collocated sampler measurements be used
to calculate quarterly and annual precision estimates for each primary
sampler and for each designated method employed by each reporting
organization. Reference 2 in section 13.0 of this appendix provides
additional information and guidance on this requirement.
6.0 Filter for PM2.5 Sample Collection. Any filter
manufacturer or vendor who sells or offers to sell filters specifically
identified for use with this PM2.5 reference method shall
certify that the required number of filters from each lot of filters
offered for sale as such have been tested as specified in this section
6.0 and meet all of the following design and performance specifications.
6.1 Size. Circular, 46.2 mm diameter 0.25 mm.
6.2 Medium. Polytetrafluoroethylene (PTFE Teflon), with integral
support ring.
6.3 Support ring. Polymethylpentene (PMP) or equivalent inert
material, 0.38 0.04 mm thick, outer diameter 46.2
mm 0.25 mm, and width of 3.68 mm ( 0.00, -0.51 mm).
6.4 Pore size. 2 [micro]m as measured by ASTM F 316-94.
6.5 Filter thickness. 30 to 50 [micro]m.
6.6 Maximum pressure drop (clean filter). 30 cm H2O
column @ 16.67 L/min clean air flow.
6.7 Maximum moisture pickup. Not more than 10 [micro]g weight
increase after 24-hour exposure to air of 40 percent relative humidity,
relative to weight after 24-hour exposure to air of 35 percent relative
humidity.
6.8 Collection efficiency. Greater than 99.7 percent, as measured by
the DOP test (ASTM D 2986-91) with 0.3 [micro]m particles at the
sampler's operating face velocity.
6.9 Filter weight stability. Filter weight loss shall be less than
20 [micro]g, as measured in each of the following two tests specified in
sections 6.9.1 and 6.9.2 of this appendix. The following conditions
apply to both of these tests: Filter weight loss shall be the average
difference between the initial and the final filter weights of a random
sample of test filters selected from each lot prior to sale. The number
of filters tested shall be not less than 0.1 percent of the filters of
each manufacturing lot, or 10 filters, whichever is greater. The filters
shall be weighed under laboratory conditions and shall have had no air
sample passed through them, i.e., filter blanks. Each test procedure
must include initial conditioning and weighing, the test, and final
conditioning and weighing. Conditioning and weighing shall be in
accordance with sections 8.0 through 8.2 of this appendix and general
guidance provided in reference 2 of section 13.0 of this appendix.
6.9.1 Test for loose, surface particle contamination. After the
initial weighing, install each test filter, in turn, in a filter
cassette (Figures L-27, L-28, and L-29 of this appendix) and drop the
cassette from a height of 25 cm to a flat hard surface, such as a
particle-free wood bench. Repeat two times, for a total of three drop
tests for each test filter. Remove the test filter from the cassette and
weigh the filter. The average change in weight must be less than 20
[micro]g.
6.9.2 Test for temperature stability. After weighing each filter,
place the test filters in a drying oven set at 40 [deg]C 2 [deg]C for not less than 48 hours. Remove, condition,
and reweigh each test filter. The average change in weight must be less
than 20 [micro]g.
6.10 Alkalinity. Less than 25 microequivalents/gram of filter, as
measured by the guidance given in reference 2 in section 13.0 of this
appendix.
6.11 Supplemental requirements. Although not required for
determination of PM2.5 mass concentration under this
reference method, additional specifications for the filter must be
developed by users who intend to subject PM2.5 filter samples
to subsequent chemical analysis. These supplemental specifications
include background chemical contamination of the filter and any other
filter parameters that may be required by the method of chemical
analysis. All such supplemental filter specifications must be compatible
with and secondary to the primary filter specifications given in this
section 6.0 of this appendix.
7.0 PM2.5 Sampler.
7.1 Configuration. The sampler shall consist of a sample air inlet,
downtube, particle size separator (impactor), filter holder assembly,
air pump and flow rate control system, flow rate measurement device,
ambient and filter temperature monitoring system, barometric pressure
measurement system, timer, outdoor environmental enclosure, and suitable
mechanical, electrical, or electronic control capability to meet or
exceed the design and functional performance as specified in this
section 7.0 of this appendix. The performance specifications require
that the sampler:
(a) Provide automatic control of sample volumetric flow rate and
other operational parameters.
(b) Monitor these operational parameters as well as ambient
temperature and pressure.
(c) Provide this information to the sampler operator at the end of
each sample period in
[[Page 76]]
digital form, as specified in table L-1 of section 7.4.19 of this
appendix.
7.2 Nature of specifications. The PM2.5 sampler is
specified by a combination of design and performance requirements. The
sample inlet, downtube, particle size discriminator, filter cassette,
and the internal configuration of the filter holder assembly are
specified explicitly by design figures and associated mechanical
dimensions, tolerances, materials, surface finishes, assembly
instructions, and other necessary specifications. All other aspects of
the sampler are specified by required operational function and
performance, and the design of these other aspects (including the design
of the lower portion of the filter holder assembly) is optional, subject
to acceptable operational performance. Test procedures to demonstrate
compliance with both the design and performance requirements are set
forth in subpart E of part 53 of this chapter.
7.3 Design specifications. Except as indicated in this section 7.3
of this appendix, these components must be manufactured or reproduced
exactly as specified, in an ISO 9001-registered facility, with
registration initially approved and subsequently maintained during the
period of manufacture. See Sec. 53.1(t) of this chapter for the
definition of an ISO-registered facility. Minor modifications or
variances to one or more components that clearly would not affect the
aerodynamic performance of the inlet, downtube, impactor, or filter
cassette will be considered for specific approval. Any such proposed
modifications shall be described and submitted to the EPA for specific
individual acceptability either as part of a reference or equivalent
method application under part 53 of this chapter or in writing in
advance of such an intended application under part 53 of this chapter.
7.3.1 Sample inlet assembly. The sample inlet assembly, consisting
of the inlet, downtube, and impactor shall be configured and assembled
as indicated in Figure L-1 of this appendix and shall meet all
associated requirements. A portion of this assembly shall also be
subject to the maximum overall sampler leak rate specification under
section 7.4.6 of this appendix.
7.3.2 Inlet. The sample inlet shall be fabricated as indicated in
Figures L-2 through L-18 of this appendix and shall meet all associated
requirements.
7.3.3 Downtube. The downtube shall be fabricated as indicated in
Figure L-19 of this appendix and shall meet all associated requirements.
7.3.4 Impactor.
7.3.4.1 The impactor (particle size separator) shall be fabricated
as indicated in Figures L-20 through L-24 of this appendix and shall
meet all associated requirements. Following the manufacture and
finishing of each upper impactor housing (Figure L-21 of this appendix),
the dimension of the impaction jet must be verified by the manufacturer
using Class ZZ go/no-go plug gauges that are traceable to NIST.
7.3.4.2 Impactor filter specifications:
(a) Size. Circular, 35 to 37 mm diameter.
(b) Medium. Borosilicate glass fiber, without binder.
(c) Pore size. 1 to 1.5 micrometer, as measured by ASTM F 316-80.
(d) Thickness. 300 to 500 micrometers.
7.3.4.3 Impactor oil specifications:
(a) Composition. Tetramethyltetraphenyltrisiloxane, single-compound
diffusion oil.
(b) Vapor pressure. Maximum 2x10-8 mm Hg at 25 [deg]C.
(c) Viscosity. 36 to 40 centistokes at 25 [deg]C.
(d) Density. 1.06 to 1.07 g/cm\3\ at 25 [deg]C.
(e) Quantity. 1 mL 0.1 mL.
7.3.5 Filter holder assembly. The sampler shall have a sample filter
holder assembly to adapt and seal to the down tube and to hold and seal
the specified filter, under section 6.0 of this appendix, in the sample
air stream in a horizontal position below the downtube such that the
sample air passes downward through the filter at a uniform face
velocity. The upper portion of this assembly shall be fabricated as
indicated in Figures L-25 and L-26 of this appendix and shall accept and
seal with the filter cassette, which shall be fabricated as indicated in
Figures L-27 through L-29 of this appendix.
(a) The lower portion of the filter holder assembly shall be of a
design and construction that:
(1) Mates with the upper portion of the assembly to complete the
filter holder assembly,
(2) Completes both the external air seal and the internal filter
cassette seal such that all seals are reliable over repeated filter
changings, and
(3) Facilitates repeated changing of the filter cassette by the
sampler operator.
(b) Leak-test performance requirements for the filter holder
assembly are included in section 7.4.6 of this appendix.
(c) If additional or multiple filters are stored in the sampler as
part of an automatic sequential sample capability, all such filters,
unless they are currently and directly installed in a sampling channel
or sampling configuration (either active or inactive), shall be covered
or (preferably) sealed in such a way as to:
(1) Preclude significant exposure of the filter to possible
contamination or accumulation of dust, insects, or other material that
may be present in the ambient air, sampler, or sampler ventilation air
during storage periods either before or after sampling; and
(2) To minimize loss of volatile or semi-volatile PM sample
components during storage of the filter following the sample period.
[[Page 77]]
7.3.6 Flow rate measurement adapter. A flow rate measurement adapter
as specified in Figure L-30 of this appendix shall be furnished with
each sampler.
7.3.7 Surface finish. All internal surfaces exposed to sample air
prior to the filter shall be treated electrolytically in a sulfuric acid
bath to produce a clear, uniform anodized surface finish of not less
than 1000 mg/ft\2\ (1.08 mg/cm\2\) in accordance with military standard
specification (mil. spec.) 8625F, Type II, Class 1 in reference 4 of
section 13.0 of this appendix. This anodic surface coating shall not be
dyed or pigmented. Following anodization, the surfaces shall be sealed
by immersion in boiling deionized water for not less than 15 minutes.
Section 53.51(d)(2) of this chapter should also be consulted.
7.3.8 Sampling height. The sampler shall be equipped with legs, a
stand, or other means to maintain the sampler in a stable, upright
position and such that the center of the sample air entrance to the
inlet, during sample collection, is maintained in a horizontal plane and
is 2.0 0.2 meters above the floor or other
horizontal supporting surface. Suitable bolt holes, brackets, tie-downs,
or other means should be provided to facilitate mechanically securing
the sample to the supporting surface to prevent toppling of the sampler
due to wind.
7.4 Performance specifications.
7.4.1 Sample flow rate. Proper operation of the impactor requires
that specific air velocities be maintained through the device.
Therefore, the design sample air flow rate through the inlet shall be
16.67 L/min (1.000 m\3\/hour) measured as actual volumetric flow rate at
the temperature and pressure of the sample air entering the inlet.
7.4.2 Sample air flow rate control system. The sampler shall have a
sample air flow rate control system which shall be capable of providing
a sample air volumetric flow rate within the specified range, under
section 7.4.1 of this appendix, for the specified filter, under section
6.0 of this appendix, at any atmospheric conditions specified, under
section 7.4.7 of this appendix, at a filter pressure drop equal to that
of a clean filter plus up to 75 cm water column (55 mm Hg), and over the
specified range of supply line voltage, under section 7.4.15.1 of this
appendix. This flow control system shall allow for operator adjustment
of the operational flow rate of the sampler over a range of at least
15 percent of the flow rate specified in section
7.4.1 of this appendix.
7.4.3 Sample flow rate regulation. The sample flow rate shall be
regulated such that for the specified filter, under section 6.0 of this
appendix, at any atmospheric conditions specified, under section 7.4.7
of this appendix, at a filter pressure drop equal to that of a clean
filter plus up to 75 cm water column (55 mm Hg), and over the specified
range of supply line voltage, under section 7.4.15.1 of this appendix,
the flow rate is regulated as follows:
7.4.3.1 The volumetric flow rate, measured or averaged over
intervals of not more than 5 minutes over a 24-hour period, shall not
vary more than 5 percent from the specified 16.67
L/min flow rate over the entire sample period.
7.4.3.2 The coefficient of variation (sample standard deviation
divided by the mean) of the flow rate, measured over a 24-hour period,
shall not be greater than 2 percent.
7.4.3.3 The amplitude of short-term flow rate pulsations, such as
may originate from some types of vacuum pumps, shall be attenuated such
that they do not cause significant flow measurement error or affect the
collection of particles on the particle collection filter.
7.4.4 Flow rate cut off. The sampler's sample air flow rate control
system shall terminate sample collection and stop all sample flow for
the remainder of the sample period in the event that the sample flow
rate deviates by more than 10 percent from the sampler design flow rate
specified in section 7.4.1 of this appendix for more than 60 seconds.
However, this sampler cut-off provision shall not apply during periods
when the sampler is inoperative due to a temporary power interruption,
and the elapsed time of the inoperative period shall not be included in
the total sample time measured and reported by the sampler, under
section 7.4.13 of this appendix.
7.4.5 Flow rate measurement.
7.4.5.1 The sampler shall provide a means to measure and indicate
the instantaneous sample air flow rate, which shall be measured as
volumetric flow rate at the temperature and pressure of the sample air
entering the inlet, with an accuracy of 2 percent.
The measured flow rate shall be available for display to the sampler
operator at any time in either sampling or standby modes, and the
measurement shall be updated at least every 30 seconds. The sampler
shall also provide a simple means by which the sampler operator can
manually start the sample flow temporarily during non-sampling modes of
operation, for the purpose of checking the sample flow rate or the flow
rate measurement system.
7.4.5.2 During each sample period, the sampler's flow rate
measurement system shall automatically monitor the sample volumetric
flow rate, obtaining flow rate measurements at intervals of not greater
than 30 seconds.
(a) Using these interval flow rate measurements, the sampler shall
determine or calculate the following flow-related parameters, scaled in
the specified engineering units:
(1) The instantaneous or interval-average flow rate, in L/min.
(2) The value of the average sample flow rate for the sample period,
in L/min.
[[Page 78]]
(3) The value of the coefficient of variation (sample standard
deviation divided by the average) of the sample flow rate for the sample
period, in percent.
(4) The occurrence of any time interval during the sample period in
which the measured sample flow rate exceeds a range of 5 percent of the average flow rate for the sample period
for more than 5 minutes, in which case a warning flag indicator shall be
set.
(5) The value of the integrated total sample volume for the sample
period, in m\3\.
(b) Determination or calculation of these values shall properly
exclude periods when the sampler is inoperative due to temporary
interruption of electrical power, under section 7.4.13 of this appendix,
or flow rate cut off, under section 7.4.4 of this appendix.
(c) These parameters shall be accessible to the sampler operator as
specified in table L-1 of section 7.4.19 of this appendix. In addition,
it is strongly encouraged that the flow rate for each 5-minute interval
during the sample period be available to the operator following the end
of the sample period.
7.4.6 Leak test capability.
7.4.6.1 External leakage. The sampler shall include an external air
leak-test capability consisting of components, accessory hardware,
operator interface controls, a written procedure in the associated
Operation/Instruction Manual, under section 7.4.18 of this appendix, and
all other necessary functional capability to permit and facilitate the
sampler operator to conveniently carry out a leak test of the sampler at
a field monitoring site without additional equipment. The sampler
components to be subjected to this leak test include all components and
their interconnections in which external air leakage would or could
cause an error in the sampler's measurement of the total volume of
sample air that passes through the sample filter.
(a) The suggested technique for the operator to use for this leak
test is as follows:
(1) Remove the sampler inlet and installs the flow rate measurement
adapter supplied with the sampler, under section 7.3.6 of this appendix.
(2) Close the valve on the flow rate measurement adapter and use the
sampler air pump to draw a partial vacuum in the sampler, including (at
least) the impactor, filter holder assembly (filter in place), flow
measurement device, and interconnections between these devices, of at
least 55 mm Hg (75 cm water column), measured at a location downstream
of the filter holder assembly.
(3) Plug the flow system downstream of these components to isolate
the components under vacuum from the pump, such as with a built-in
valve.
(4) Stop the pump.
(5) Measure the trapped vacuum in the sampler with a built-in
pressure measuring device.
(6) (i) Measure the vacuum in the sampler with the built-in pressure
measuring device again at a later time at least 10 minutes after the
first pressure measurement.
(ii) Caution: Following completion of the test, the adaptor valve
should be opened slowly to limit the flow rate of air into the sampler.
Excessive air flow rate may blow oil out of the impactor.
(7) Upon completion of the test, open the adaptor valve, remove the
adaptor and plugs, and restore the sampler to the normal operating
configuration.
(b) The associated leak test procedure shall require that for
successful passage of this test, the difference between the two pressure
measurements shall not be greater than the number of mm of Hg specified
for the sampler by the manufacturer, based on the actual internal volume
of the sampler, that indicates a leak of less than 80 mL/min.
(c) Variations of the suggested technique or an alternative external
leak test technique may be required for samplers whose design or
configuration would make the suggested technique impossible or
impractical. The specific proposed external leak test procedure, or
particularly an alternative leak test technique, proposed for a
particular candidate sampler may be described and submitted to the EPA
for specific individual acceptability either as part of a reference or
equivalent method application under part 53 of this chapter or in
writing in advance of such an intended application under part 53 of this
chapter.
7.4.6.2 Internal, filter bypass leakage. The sampler shall include
an internal, filter bypass leak-check capability consisting of
components, accessory hardware, operator interface controls, a written
procedure in the Operation/Instruction Manual, and all other necessary
functional capability to permit and facilitate the sampler operator to
conveniently carry out a test for internal filter bypass leakage in the
sampler at a field monitoring site without additional equipment. The
purpose of the test is to determine that any portion of the sample flow
rate that leaks past the sample filter without passing through the
filter is insignificant relative to the design flow rate for the
sampler.
(a) The suggested technique for the operator to use for this leak
test is as follows:
(1) Carry out an external leak test as provided under section
7.4.6.1 of this appendix which indicates successful passage of the
prescribed external leak test.
(2) Install a flow-impervious membrane material in the filter
cassette, either with or without a filter, as appropriate, which
effectively prevents air flow through the filter.
(3) Use the sampler air pump to draw a partial vacuum in the
sampler, downstream of the filter holder assembly, of at least 55 mm Hg
(75 cm water column).
[[Page 79]]
(4) Plug the flow system downstream of the filter holder to isolate
the components under vacuum from the pump, such as with a built-in
valve.
(5) Stop the pump.
(6) Measure the trapped vacuum in the sampler with a built-in
pressure measuring device.
(7) Measure the vacuum in the sampler with the built-in pressure
measuring device again at a later time at least 10 minutes after the
first pressure measurement.
(8) Remove the flow plug and membrane and restore the sampler to the
normal operating configuration.
(b) The associated leak test procedure shall require that for
successful passage of this test, the difference between the two pressure
measurements shall not be greater than the number of mm of Hg specified
for the sampler by the manufacturer, based on the actual internal volume
of the portion of the sampler under vacuum, that indicates a leak of
less than 80 mL/min.
(c) Variations of the suggested technique or an alternative
internal, filter bypass leak test technique may be required for samplers
whose design or configuration would make the suggested technique
impossible or impractical. The specific proposed internal leak test
procedure, or particularly an alternative internal leak test technique
proposed for a particular candidate sampler may be described and
submitted to the EPA for specific individual acceptability either as
part of a reference or equivalent method application under part 53 of
this chapter or in writing in advance of such intended application under
part 53 of this chapter.
7.4.7 Range of operational conditions. The sampler is required to
operate properly and meet all requirements specified in this appendix
over the following operational ranges.
7.4.7.1 Ambient temperature. -30 to =45 [deg]C (Note: Although for
practical reasons, the temperature range over which samplers are
required to be tested under part 53 of this chapter is -20 to =40
[deg]C, the sampler shall be designed to operate properly over this
wider temperature range.).
7.4.7.2 Ambient relative humidity. 0 to 100 percent.
7.4.7.3 Barometric pressure range. 600 to 800 mm Hg.
7.4.8 Ambient temperature sensor. The sampler shall have capability
to measure the temperature of the ambient air surrounding the sampler
over the range of -30 to =45 [deg]C, with a resolution of 0.1 [deg]C and
accuracy of 2.0 [deg]C, referenced as described in
reference 3 in section 13.0 of this appendix, with and without maximum
solar insolation.
7.4.8.1 The ambient temperature sensor shall be mounted external to
the sampler enclosure and shall have a passive, naturally ventilated sun
shield. The sensor shall be located such that the entire sun shield is
at least 5 cm above the horizontal plane of the sampler case or
enclosure (disregarding the inlet and downtube) and external to the
vertical plane of the nearest side or protuberance of the sampler case
or enclosure. The maximum temperature measurement error of the ambient
temperature measurement system shall be less than 1.6 [deg]C at 1 m/s
wind speed and 1000 W/m2 solar radiation intensity.
7.4.8.2 The ambient temperature sensor shall be of such a design and
mounted in such a way as to facilitate its convenient dismounting and
immersion in a liquid for calibration and comparison to the filter
temperature sensor, under section 7.4.11 of this appendix.
7.4.8.3 This ambient temperature measurement shall be updated at
least every 30 seconds during both sampling and standby (non-sampling)
modes of operation. A visual indication of the current (most recent)
value of the ambient temperature measurement, updated at least every 30
seconds, shall be available to the sampler operator during both sampling
and standby (non-sampling) modes of operation, as specified in table L-1
of section 7.4.19 of this appendix.
7.4.8.4 This ambient temperature measurement shall be used for the
purpose of monitoring filter temperature deviation from ambient
temperature, as required by section 7.4.11 of this appendix, and may be
used for purposes of effecting filter temperature control, under section
7.4.10 of this appendix, or computation of volumetric flow rate, under
sections 7.4.1 to 7.4.5 of this appendix, if appropriate.
7.4.8.5 Following the end of each sample period, the sampler shall
report the maximum, minimum, and average temperature for the sample
period, as specified in table L-1 of section 7.4.19 of this appendix.
7.4.9 Ambient barometric sensor. The sampler shall have capability
to measure the barometric pressure of the air surrounding the sampler
over a range of 600 to 800 mm Hg referenced as described in reference 3
in section 13.0 of this appendix; also see part 53, subpart E of this
chapter. This barometric pressure measurement shall have a resolution of
5 mm Hg and an accuracy of 10 mm Hg and shall be
updated at least every 30 seconds. A visual indication of the value of
the current (most recent) barometric pressure measurement, updated at
least every 30 seconds, shall be available to the sampler operator
during both sampling and standby (non-sampling) modes of operation, as
specified in table L-1 of section 7.4.19 of this appendix. This
barometric pressure measurement may be used for purposes of computation
of volumetric flow rate, under sections 7.4.1 to 7.4.5 of this appendix,
if appropriate. Following the end of a sample period, the sampler shall
report the maximum, minimum, and mean barometric pressures for the
sample period,
[[Page 80]]
as specified in table L-1 of section 7.4.19 of this appendix.
7.4.10 Filter temperature control (sampling and post-sampling). The
sampler shall provide a means to limit the temperature rise of the
sample filter (all sample filters for sequential samplers), from
insolation and other sources, to no more 5 [deg]C above the temperature
of the ambient air surrounding the sampler, during both sampling and
post-sampling periods of operation. The post-sampling period is the non-
sampling period between the end of the active sampling period and the
time of retrieval of the sample filter by the sampler operator.
7.4.11 Filter temperature sensor(s).
7.4.11.1 The sampler shall have the capability to monitor the
temperature of the sample filter (all sample filters for sequential
samplers) over the range of -30 to =45 [deg]C during both sampling and
non-sampling periods. While the exact location of this temperature
sensor is not explicitly specified, the filter temperature measurement
system must demonstrate agreement, within 1 [deg]C, with a test
temperature sensor located within 1 cm of the center of the filter
downstream of the filter during both sampling and non-sampling modes, as
specified in the filter temperature measurement test described in part
53, subpart E of this chapter. This filter temperature measurement shall
have a resolution of 0.1 [deg]C and accuracy of 1.0 [deg]C, referenced as described in reference 3 in
section 13.0 of this appendix. This temperature sensor shall be of such
a design and mounted in such a way as to facilitate its reasonably
convenient dismounting and immersion in a liquid for calibration and
comparison to the ambient temperature sensor under section 7.4.8 of this
appendix.
7.4.11.2 The filter temperature measurement shall be updated at
least every 30 seconds during both sampling and standby (non-sampling)
modes of operation. A visual indication of the current (most recent)
value of the filter temperature measurement, updated at least every 30
seconds, shall be available to the sampler operator during both sampling
and standby (non-sampling) modes of operation, as specified in table L-1
of section 7.4.19 of this appendix.
7.4.11.3 For sequential samplers, the temperature of each filter
shall be measured individually unless it can be shown, as specified in
the filter temperature measurement test described in Sec. 53.57 of this
chapter, that the temperature of each filter can be represented by fewer
temperature sensors.
7.4.11.4 The sampler shall also provide a warning flag indicator
following any occurrence in which the filter temperature (any filter
temperature for sequential samplers) exceeds the ambient temperature by
more than 5 [deg]C for more than 30 consecutive minutes during either
the sampling or post-sampling periods of operation, as specified in
table L-1 of section 7.4.19 of this appendix, under section 10.12 of
this appendix, regarding sample validity when a warning flag occurs. It
is further recommended (not required) that the sampler be capable of
recording the maximum differential between the measured filter
temperature and the ambient temperature and its time and date of
occurrence during both sampling and post-sampling (non-sampling) modes
of operation and providing for those data to be accessible to the
sampler operator following the end of the sample period, as suggested in
table L-1 of section 7.4.19 of this appendix.
7.4.12 Clock/timer system.
(a) The sampler shall have a programmable real-time clock timing/
control system that:
(1) Is capable of maintaining local time and date, including year,
month, day-of-month, hour, minute, and second to an accuracy of 1.0 minute per month.
(2) Provides a visual indication of the current system time,
including year, month, day-of-month, hour, and minute, updated at least
each minute, for operator verification.
(3) Provides appropriate operator controls for setting the correct
local time and date.
(4) Is capable of starting the sample collection period and sample
air flow at a specific, operator-settable time and date, and stopping
the sample air flow and terminating the sampler collection period 24
hours (1440 minutes) later, or at a specific, operator-settable time and
date.
(b) These start and stop times shall be readily settable by the
sampler operator to within 1.0 minute. The system
shall provide a visual indication of the current start and stop time
settings, readable to 1.0 minute, for verification
by the operator, and the start and stop times shall also be available
via the data output port, as specified in table L-1 of section 7.4.19 of
this appendix. Upon execution of a programmed sample period start, the
sampler shall automatically reset all sample period information and
warning flag indications pertaining to a previous sample period. Refer
also to section 7.4.15.4 of this appendix regarding retention of current
date and time and programmed start and stop times during a temporary
electrical power interruption.
7.4.13 Sample time determination. The sampler shall be capable of
determining the elapsed sample collection time for each PM2.5
sample, accurate to within 1.0 minute, measured as
the time between the start of the sampling period, under section 7.4.12
of this appendix and the termination of the sample period, under section
7.4.12 of this appendix or section 7.4.4 of this appendix. This elapsed
sample time shall not include periods when the sampler is inoperative
due to a temporary interruption of electrical power, under section
7.4.15.4 of this appendix. In the event that the elapsed sample time
determined for the sample period is not within the
[[Page 81]]
range specified for the required sample period in section 3.3 of this
appendix, the sampler shall set a warning flag indicator. The date and
time of the start of the sample period, the value of the elapsed sample
time for the sample period, and the flag indicator status shall be
available to the sampler operator following the end of the sample
period, as specified in table L-1 of section 7.4.19 of this appendix.
7.4.14 Outdoor environmental enclosure. The sampler shall have an
outdoor enclosure (or enclosures) suitable to protect the filter and
other non-weatherproof components of the sampler from precipitation,
wind, dust, extremes of temperature and humidity; to help maintain
temperature control of the filter (or filters, for sequential samplers);
and to provide reasonable security for sampler components and settings.
7.4.15 Electrical power supply.
7.4.15.1 The sampler shall be operable and function as specified
herein when operated on an electrical power supply voltage of 105 to 125
volts AC (RMS) at a frequency of 59 to 61 Hz. Optional operation as
specified at additional power supply voltages and/or frequencies shall
not be precluded by this requirement.
7.4.15.2 The design and construction of the sampler shall comply
with all applicable National Electrical Code and Underwriters
Laboratories electrical safety requirements.
7.4.15.3 The design of all electrical and electronic controls shall
be such as to provide reasonable resistance to interference or
malfunction from ordinary or typical levels of stray electromagnetic
fields (EMF) as may be found at various monitoring sites and from
typical levels of electrical transients or electronic noise as may often
or occasionally be present on various electrical power lines.
7.4.15.4 In the event of temporary loss of electrical supply power
to the sampler, the sampler shall not be required to sample or provide
other specified functions during such loss of power, except that the
internal clock/timer system shall maintain its local time and date
setting within 1 minute per week, and the sampler
shall retain all other time and programmable settings and all data
required to be available to the sampler operator following each sample
period for at least 7 days without electrical supply power. When
electrical power is absent at the operator-set time for starting a
sample period or is interrupted during a sample period, the sampler
shall automatically start or resume sampling when electrical power is
restored, if such restoration of power occurs before the operator-set
stop time for the sample period.
7.4.15.5 The sampler shall have the capability to record and retain
a record of the year, month, day-of-month, hour, and minute of the start
of each power interruption of more than 1 minute duration, up to 10 such
power interruptions per sample period. (More than 10 such power
interruptions shall invalidate the sample, except where an exceedance is
measured, under section 3.3 of this appendix.) The sampler shall provide
for these power interruption data to be available to the sampler
operator following the end of the sample period, as specified in table
L-1 of section 7.4.19 of this appendix.
7.4.16 Control devices and operator interface. The sampler shall
have mechanical, electrical, or electronic controls, control devices,
electrical or electronic circuits as necessary to provide the timing,
flow rate measurement and control, temperature control, data storage and
computation, operator interface, and other functions specified.
Operator-accessible controls, data displays, and interface devices shall
be designed to be simple, straightforward, reliable, and easy to learn,
read, and operate under field conditions. The sampler shall have
provision for operator input and storage of up to 64 characters of
numeric (or alphanumeric) data for purposes of site, sampler, and sample
identification. This information shall be available to the sampler
operator for verification and change and for output via the data output
port along with other data following the end of a sample period, as
specified in table L-1 of section 7.4.19 of this appendix. All data
required to be available to the operator following a sample collection
period or obtained during standby mode in a post-sampling period shall
be retained by the sampler until reset, either manually by the operator
or automatically by the sampler upon initiation of a new sample
collection period.
7.4.17 Data output port requirement. The sampler shall have a
standard RS-232C data output connection through which digital data may
be exported to an external data storage or transmission device. All
information which is required to be available at the end of each sample
period shall be accessible through this data output connection. The
information that shall be accessible though this output port is
summarized in table L-1 of section 7.4.19 of this appendix. Since no
specific format for the output data is provided, the sampler
manufacturer or vendor shall make available to sampler purchasers
appropriate computer software capable of receiving exported sampler data
and correctly translating the data into a standard spreadsheet format
and optionally any other formats as may be useful to sampler users. This
requirement shall not preclude the sampler from offering other types of
output connections in addition to the required RS-232C port.
7.4.18 Operation/instruction manual. The sampler shall include an
associated comprehensive operation or instruction manual, as required by
part 53 of this chapter, which includes detailed operating instructions
on
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the setup, operation, calibration, and maintenance of the sampler. This
manual shall provide complete and detailed descriptions of the
operational and calibration procedures prescribed for field use of the
sampler and all instruments utilized as part of this reference method.
The manual shall include adequate warning of potential safety hazards
that may result from normal use or malfunction of the method and a
description of necessary safety precautions. The manual shall also
include a clear description of all procedures pertaining to
installation, operation, periodic and corrective maintenance, and
troubleshooting, and shall include parts identification diagrams.
7.4.19 Data reporting requirements. The various information that the
sampler is required to provide and how it is to be provided is
summarized in the following table L-1.
Table L-1--Summary of Information To Be Provided By the Sampler
--------------------------------------------------------------------------------------------------------------------------------------------------------
Availability Format
Appendix L section -------------------------------------------------------------------------------------------------
Information to be provided reference End of Visual Data output
Anytime \1\ period \2\ display \3\ \4\ Digital reading \5\ Units
--------------------------------------------------------------------------------------------------------------------------------------------------------
Flow rate, 30-second maximum 7.4.5.1............ [bcheck] ............ [bcheck] * XX.X............... L/min
interval.
Flow rate, average for the sample 7.4.5.2............ * [bcheck] * [bcheck] XX.X............... L/min
period.
Flow rate, CV, for sample period. 7.4.5.2............ * [bcheck] * [bcheck][msh XX.X............... %
box]
Flow rate, 5-min. average out of 7.4.5.2............ [bcheck] [bcheck] [bcheck] [bcheck][msh On/Off............. ...................
spec. (FLAG \6\). box]
Sample volume, total............. 7.4.5.2............ * [bcheck] [bcheck] [bcheck][msh XX.X............... m\3\
box]
Temperature, ambient, 30-second 7.4.8.............. [bcheck] ............ [bcheck] ............ XX.X............... [deg]C
interval.
Temperature, ambient, min., max., 7.4.8.............. * [bcheck] [bcheck] [bcheck][msh XX.X............... [deg]C
average for the sample period. box]
Baro pressure, ambient, 30-second 7.4.9.............. [bcheck] ............ [bcheck] ............ XXX................ mm Hg
interval.
Baro pressure, ambient, min., 7.4.9.............. * [bcheck] [bcheck] [bcheck][msh XXX................ mm Hg
max., average for the sample box]
period.
Filter temperature, 30-second 7.4.11............. [bcheck] ............ [bcheck] ............ XX.X............... [deg]C
interval.
Filter temperature differential, 7.4.11............. * [bcheck] [bcheck] [bcheck][msh On/Off............. ...................
30-second interval, out of spec. box]
(FLAG \6\).
Filter temperature, maximum 7.4.11............. * * * * X.X, YY/MM/DD HH:mm [deg]C, Yr./Mon./
differential from ambient, date, Day Hrs. min
time of occurrence.
Date and time.................... 7.4.12............. [bcheck] ............ [bcheck] ............ YY/MM/DD HH:mm..... Yr./Mon./Day Hrs.
min
Sample start and stop time 7.4.12............. [bcheck] [bcheck] [bcheck] [bcheck] YY/MM/DD HH:mm..... Yr./Mon./Day Hrs.
settings. min
Sample period start time......... 7.4.12............. ............ [bcheck] [bcheck] [bcheck][msh YYYY/MM/DD HH:mm... Yr./Mon./Day Hrs.
box] min
Elapsed sample time.............. 7.4.13............. * [bcheck] [bcheck] [bcheck][msh HH:mm.............. Hrs. min
box]
Elapsed sample time, out of spec. 7.4.13............. ............ [bcheck] [bcheck] [bcheck][msh On/Off............. ...................
(FLAG \6\). box]
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Power interruptions <=1 min., 7.4.15.5........... * [bcheck] * [bcheck] 1HH:mm, 2HH:mm, etc Hrs. min
start time of first 10. ....
User-entered information, such as 7.4.16............. [bcheck] [bcheck] [bcheck] [bcheck][msh As entered......... ...................
sampler and site identification. box]
--------------------------------------------------------------------------------------------------------------------------------------------------------
[bcheck] Provision of this information is required.
*Provision of this information is optional. If information related to the entire sample period is optionally provided prior to the end of the sample
period, the value provided should be the value calculated for the portion of the sampler period completed up to the time the information is provided.
[mshbox] Indicates that this information is also required to be provided to the AIRS data bank; see Sec. Sec. 58.26 and 58.35 of this chapter.
\1\ Information is required to be available to the operator at any time the sampler is operating, whether sampling or not.
\2\ Information relates to the entire sampler period and must be provided following the end of the sample period until reset manually by the operator or
automatically by the sampler upon the start of a new sample period.
\3\ Information shall be available to the operator visually.
\4\ Information is to be available as digital data at the sampler's data output port specified in section 7.4.16 of this appendix following the end of
the sample period until reset manually by the operator or automatically by the sampler upon the start of a new sample period.
\5\ Digital readings, both visual and data output, shall have not less than the number of significant digits and resolution specified.
\6\ Flag warnings may be displayed to the operator by a single-flag indicator or each flag may be displayed individually. Only a set (on) flag warning
must be indicated; an off (unset) flag may be indicated by the absence of a flag warning. Sampler users should refer to section 10.12 of this appendix
regarding the validity of samples for which the sampler provided an associated flag warning.
8.0 Filter Weighing. See reference 2 in section 13.0 of this
appendix, for additional, more detailed guidance.
8.1 Analytical balance. The analytical balance used to weigh filters
must be suitable for weighing the type and size of filters specified,
under section 6.0 of this appendix, and have a readability of 1 [micro]g. The balance shall be calibrated as specified
by the manufacturer at installation and recalibrated immediately prior
to each weighing session. See reference 2 in section 13.0 of this
appendix for additional guidance.
8.2 Filter conditioning. All sample filters used shall be
conditioned immediately before both the pre- and post-sampling weighings
as specified below. See reference 2 in section 13.0 of this appendix for
additional guidance.
8.2.1 Mean temperature. 20 - 23 [deg]C.
8.2.2 Temperature control. 2 [deg]C over 24
hours.
8.2.3 Mean humidity. Generally, 30-40 percent relative humidity;
however, where it can be shown that the mean ambient relative humidity
during sampling is less than 30 percent, conditioning is permissible at
a mean relative humidity within 5 relative
humidity percent of the mean ambient relative humidity during sampling,
but not less than 20 percent.
8.2.4 Humidity control. 5 relative humidity
percent over 24 hours.
8.2.5 Conditioning time. Not less than 24 hours.
8.3 Weighing procedure.
8.3.1 New filters should be placed in the conditioning environment
immediately upon arrival and stored there until the pre-sampling
weighing. See reference 2 in section 13.0 of this appendix for
additional guidance.
8.3.2 The analytical balance shall be located in the same controlled
environment in which the filters are conditioned. The filters shall be
weighed immediately following the conditioning period without
intermediate or transient exposure to other conditions or environments.
8.3.3 Filters must be conditioned at the same conditions (humidity
within 5 relative humidity percent) before both
the pre- and post-sampling weighings.
8.3.4 Both the pre- and post-sampling weighings should be carried
out on the same analytical balance, using an effective technique to
neutralize static charges on the filter, under reference 2 in section
13.0 of this appendix. If possible, both weighings should be carried out
by the same analyst.
8.3.5 The pre-sampling (tare) weighing shall be within 30 days of
the sampling period.
8.3.6 The post-sampling conditioning and weighing shall be completed
within 240 hours (10 days) after the end of the sample period, unless
the filter sample is maintained at 4 [deg]C or less during the entire
time between retrieval from the sampler and the start of the
conditioning, in which case the period shall not exceed 30 days.
Reference 2 in section 13.0 of this appendix has additional guidance on
transport of cooled filters.
8.3.7 Filter blanks.
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8.3.7.1 New field blank filters shall be weighed along with the pre-
sampling (tare) weighing of each lot of PM2.5 filters. These
blank filters shall be transported to the sampling site, installed in
the sampler, retrieved from the sampler without sampling, and reweighed
as a quality control check.
8.3.7.2 New laboratory blank filters shall be weighed along with the
pre-sampling (tare) weighing of each set of PM2.5 filters.
These laboratory blank filters should remain in the laboratory in
protective containers during the field sampling and should be reweighed
as a quality control check.
8.3.8 Additional guidance for proper filter weighing and related
quality assurance activities is provided in reference 2 in section 13.0
of this appendix.
9.0 Calibration. Reference 2 in section 13.0 of this appendix
contains additional guidance.
9.1 General requirements.
9.1.1 Multipoint calibration and single-point verification of the
sampler's flow rate measurement device must be performed periodically to
establish and maintain traceability of subsequent flow measurements to a
flow rate standard.
9.1.2 An authoritative flow rate standard shall be used for
calibrating or verifying the sampler's flow rate measurement device with
an accuracy of 2 percent. The flow rate standard
shall be a separate, stand-alone device designed to connect to the flow
rate measurement adapter, Figure L-30 of this appendix. This flow rate
standard must have its own certification and be traceable to a National
Institute of Standards and Technology (NIST) primary standard for volume
or flow rate. If adjustments to the sampler's flow rate measurement
system calibration are to be made in conjunction with an audit of the
sampler's flow measurement system, such adjustments shall be made
following the audit. Reference 2 in section 13.0 of this appendix
contains additional guidance.
9.1.3 The sampler's flow rate measurement device shall be re-
calibrated after electromechanical maintenance or transport of the
sampler.
9.2 Flow rate calibration/verification procedure.
9.2.1 PM2.5 samplers may employ various types of flow
control and flow measurement devices. The specific procedure used for
calibration or verification of the flow rate measurement device will
vary depending on the type of flow rate controller and flow rate
measurement employed. Calibration shall be in terms of actual ambient
volumetric flow rates (Qa), measured at the sampler's inlet
downtube. The generic procedure given here serves to illustrate the
general steps involved in the calibration of a PM2.5 sampler.
The sampler operation/instruction manual required under section 7.4.18
of this appendix and the Quality Assurance Handbook in reference 2 in
section 13.0 of this appendix provide more specific and detailed
guidance for calibration.
9.2.2 The flow rate standard used for flow rate calibration shall
have its own certification and be traceable to a NIST primary standard
for volume or flow rate. A calibration relationship for the flow rate
standard, e.g., an equation, curve, or family of curves relating actual
flow rate (Qa) to the flow rate indicator reading, shall be
established that is accurate to within 2 percent over the expected range
of ambient temperatures and pressures at which the flow rate standard
may be used. The flow rate standard must be re-calibrated or re-verified
at least annually.
9.2.3 The sampler flow rate measurement device shall be calibrated
or verified by removing the sampler inlet and connecting the flow rate
standard to the sampler's downtube in accordance with the operation/
instruction manual, such that the flow rate standard accurately measures
the sampler's flow rate. The sampler operator shall first carry out a
sampler leak check and confirm that the sampler passes the leak test and
then verify that no leaks exist between the flow rate standard and the
sampler.
9.2.4 The calibration relationship between the flow rate (in actual
L/min) indicated by the flow rate standard and by the sampler's flow
rate measurement device shall be established or verified in accordance
with the sampler operation/instruction manual. Temperature and pressure
corrections to the flow rate indicated by the flow rate standard may be
required for certain types of flow rate standards. Calibration of the
sampler's flow rate measurement device shall consist of at least three
separate flow rate measurements (multipoint calibration) evenly spaced
within the range of -10 percent to =10 percent of the sampler's
operational flow rate, section 7.4.1 of this appendix. Verification of
the sampler's flow rate shall consist of one flow rate measurement at
the sampler's operational flow rate. The sampler operation/instruction
manual and reference 2 in section 13.0 of this appendix provide
additional guidance.
9.2.5 If during a flow rate verification the reading of the
sampler's flow rate indicator or measurement device differs by 4 percent or more from the flow rate measured by the
flow rate standard, a new multipoint calibration shall be performed and
the flow rate verification must then be repeated.
9.2.6 Following the calibration or verification, the flow rate
standard shall be removed from the sampler and the sampler inlet shall
be reinstalled. Then the sampler's normal operating flow rate (in L/min)
shall be determined with a clean filter in place. If the flow rate
indicated by the sampler differs by 2 percent or
more from the required sampler flow rate, the sampler flow rate must be
adjusted to the required flow rate, under section 7.4.1 of this
appendix.
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9.3 Periodic calibration or verification of the calibration of the
sampler's ambient temperature, filter temperature, and barometric
pressure measurement systems is also required. Reference 3 of section
13.0 of this appendix contains additional guidance.
10.0 PM2.5 Measurement Procedure. The detailed procedure
for obtaining valid PM2.5 measurements with each specific
sampler designated as part of a reference method for PM2.5
under part 53 of this chapter shall be provided in the sampler-specific
operation or instruction manual required by section 7.4.18 of this
appendix. Supplemental guidance is provided in section 2.12 of the
Quality Assurance Handbook listed in reference 2 in section 13.0 of this
appendix. The generic procedure given here serves to illustrate the
general steps involved in the PM2.5 sample collection and
measurement, using a PM2.5 reference method sampler.
10.1 The sampler shall be set up, calibrated, and operated in
accordance with the specific, detailed guidance provided in the specific
sampler's operation or instruction manual and in accordance with a
specific quality assurance program developed and established by the
user, based on applicable supplementary guidance provided in reference 2
in section 13.0 of this appendix.
10.2 Each new sample filter shall be inspected for correct type and
size and for pinholes, particles, and other imperfections. Unacceptable
filters should be discarded. A unique identification number shall be
assigned to each filter, and an information record shall be established
for each filter. If the filter identification number is not or cannot be
marked directly on the filter, alternative means, such as a number-
identified storage container, must be established to maintain positive
filter identification.
10.3 Each filter shall be conditioned in the conditioning
environment in accordance with the requirements specified in section 8.2
of this appendix.
10.4 Following conditioning, each filter shall be weighed in
accordance with the requirements specified in section 8.0 of this
appendix and the presampling weight recorded with the filter
identification number.
10.5 A numbered and preweighed filter shall be installed in the
sampler following the instructions provided in the sampler operation or
instruction manual.
10.6 The sampler shall be checked and prepared for sample collection
in accordance with instructions provided in the sampler operation or
instruction manual and with the specific quality assurance program
established for the sampler by the user.
10.7 The sampler's timer shall be set to start the sample collection
at the beginning of the desired sample period and stop the sample
collection 24 hours later.
10.8 Information related to the sample collection (site location or
identification number, sample date, filter identification number, and
sampler model and serial number) shall be recorded and, if appropriate,
entered into the sampler.
10.9 The sampler shall be allowed to collect the PM2.5
sample during the set 24-hour time period.
10.10 Within 96 hours of the end of the sample collection period,
the filter, while still contained in the filter cassette, shall be
carefully removed from the sampler, following the procedure provided in
the sampler operation or instruction manual and the quality assurance
program, and placed in a protective container. The protective container
shall contain no loose material that could be transferred to the filter.
The protective container shall hold the filter cassette securely such
that the cover shall not come in contact with the filter's surfaces.
Reference 2 in section 13.0 of this appendix contains additional
information.
10.11 The total sample volume in actual m\3\ for the sampling period
and the elapsed sample time shall be obtained from the sampler and
recorded in accordance with the instructions provided in the sampler
operation or instruction manual. All sampler warning flag indications
and other information required by the local quality assurance program
shall also be recorded.
10.12 All factors related to the validity or representativeness of
the sample, such as sampler tampering or malfunctions, unusual
meteorological conditions, construction activity, fires or dust storms,
etc. shall be recorded as required by the local quality assurance
program. The occurrence of a flag warning during a sample period shall
not necessarily indicate an invalid sample but rather shall indicate the
need for specific review of the QC data by a quality assurance officer
to determine sample validity.
10.13 After retrieval from the sampler, the exposed filter
containing the PM2.5 sample should be transported to the
filter conditioning environment as soon as possible ideally to arrive at
the conditioning environment within 24 hours for conditioning and
subsequent weighing. During the period between filter retrieval from the
sampler and the start of the conditioning, the filter shall be
maintained as cool as practical and continuously protected from exposure
to temperatures over 25 [deg]C. See section 8.3.6 of this appendix
regarding time limits for completing the post-sampling weighing. See
reference 2 in section 13.0 of this appendix for additional guidance on
transporting filter samplers to the conditioning and weighing
laboratory.
10.14. The exposed filter containing the PM2.5 sample
shall be re-conditioned in the conditioning environment in accordance
with the requirements specified in section 8.2 of this appendix.
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10.15. The filter shall be reweighed immediately after conditioning
in accordance with the requirements specified in section 8.0 of this
appendix, and the postsampling weight shall be recorded with the filter
identification number.
10.16 The PM2.5 concentration shall be calculated as
specified in section 12.0 of this appendix.
11.0 Sampler Maintenance. The sampler shall be maintained as
described by the sampler's manufacturer in the sampler-specific
operation or instruction manual required under section 7.4.18 of this
appendix and in accordance with the specific quality assurance program
developed and established by the user based on applicable supplementary
guidance provided in reference 2 in section 13.0 of this appendix.
12.0 Calculations
12.1 (a) The PM2.5 concentration is calculated as:
PM2.5 = (Wf - Wi)/Va
where:
PM2.5 = mass concentration of PM2.5, [micro]g/
m\3\;
Wf, Wi = final and initial weights, respectively,
of the filter used to collect the PM2.5 particle sample,
[micro]g;
Va = total air volume sampled in actual volume units, as
provided by the sampler, m\3\.
Note: Total sample time must be between 1,380 and 1,500 minutes (23
and 25 hrs) for a fully valid PM2.5 sample; however, see also
section 3.3 of this appendix.
13.0 References.
1. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume I, Principles. EPA/600/R-94/038a, April 1994. Available from
CERI, ORD Publications, U.S. Environmental Protection Agency, 26 West
Martin Luther King Drive, Cincinnati, Ohio 45268.
2. Copies of section 2.12 of the Quality Assurance Handbook for Air
Pollution Measurement Systems, Volume II, Ambient Air Specific Methods,
EPA/600/R-94/038b, are available from Department E (MD-77B), U.S. EPA,
Research Triangle Park, NC 27711.
3. Quality Assurance Handbook for Air Pollution Measurement Systems,
Volume IV: Meteorological Measurements, (Revised Edition) EPA/600/R-94/
038d, March, 1995. Available from CERI, ORD Publications, U.S.
Environmental Protection Agency, 26 West Martin Luther King Drive,
Cincinnati, Ohio 45268.
4. Military standard specification (mil. spec.) 8625F, Type II,
Class 1 as listed in Department of Defense Index of Specifications and
Standards (DODISS), available from DODSSP-Customer Service,
Standardization Documents Order Desk, 700 Robbins Avenue, Building 4D,
Philadelphia, PA 1911-5094.
14.0 Figures L-1 through L-30 to Appendix L.
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Appendix M to Part 50 [Reserved]
Appendix N to Part 50--Interpretation of the National Ambient Air
Quality Standards for PM2.5
1.0 General.
(a) This appendix explains the data handling conventions and
computations necessary for determining when the annual and 24-hour
primary and secondary national ambient air quality standards for PM
specified in Sec. 50.7 of this part are met. Particulate matter is
measured in the ambient air as PM2.5 (particles with an
aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by
a reference method based on appendix L of this part, as applicable, and
designated in accordance with part 53 of this chapter, or by an
equivalent method designated in accordance with part 53 of this chapter.
Data handling and computation procedures to be used in making
comparisons between reported PM2.5 concentrations and the
levels of the PM standards are specified in the following sections.
(b) Data resulting from uncontrollable or natural events, for
example structural fires or high winds, may require special
consideration. In some cases, it may be appropriate to exclude these
data because they could result in inappropriate values to compare with
the levels of the PM standards. In other cases, it may be more
appropriate to retain the data for comparison with the level of the PM
standards and then allow the EPA to formulate the appropriate regulatory
response. Whether to exclude, retain, or make adjustments to the data
affected by uncontrollable or natural events is subject to the approval
of the appropriate Regional Administrator.
(c) The terms used in this appendix are defined as follows:
Average and mean refer to an arithmetic mean.
Daily value for PM refers to the 24-hour average concentration of
PM2.5 calculated or measured from midnight to midnight (local
time).
Designated monitors are those monitoring sites designated in a State
PM Monitoring Network Description for spatial averaging in areas opting
for spatial averaging in accordance with part 58 of this chapter.
98th percentile means the daily value out of a year of
PM2.5 monitoring data below which 98 percent of all values in
the group fall.
Year refers to a calendar year.
(d) Sections 2.1 and 2.5 of this appendix contain data handling
instructions for the option of using a spatially averaged network of
monitors for the annual standard. If spatial averaging is not considered
for an area, then the spatial average is equivalent to the annual
average of a single site and is treated accordingly in subsequent
calculations. For example, paragraph (a)(3) of section 2.1 of this
appendix could be eliminated since the spatial average would be
equivalent to the annual average.
2.0 Comparisons with the PM2.5 Standards.
2.1 Annual PM2.5 Standard.
(a) The annual PM2.5 standard is met when the 3-year
average of the spatially averaged annual means is less than or equal to
15.0 [micro]g/m\3\. The 3-year average of the spatially averaged annual
means is determined by averaging quarterly means at each monitor to
obtain the annual mean PM2.5 concentrations at each monitor,
then averaging across all designated monitors, and finally averaging for
3 consecutive years. The steps can be summarized as follows:
(1) Average 24-hour measurements to obtain quarterly means at each
monitor.
(2) Average quarterly means to obtain annual means at each monitor.
(3) Average across designated monitoring sites to obtain an annual
spatial mean for an area (this can be one site in which case the spatial
mean is equal to the annual mean).
(4) Average 3 years of annual spatial means to obtain a 3-year
average of spatially averaged annual means.
(b) In the case of spatial averaging, 3 years of spatial averages
are required to demonstrate that the standard has been met. Designated
sites with less than 3 years of data shall be included in spatial
averages for those years that data completeness requirements are met.
For the annual PM2.5 standard, a year meets data completeness
requirements when at least 75 percent of the scheduled sampling days for
each quarter have valid data. However, years with high concentrations
and more than a minimal amount of data (at least 11 samples in each
quarter) shall not be ignored just because they are comprised of
quarters with less than complete data. Thus, in computing annual
spatially averaged means, years containing quarters with at least 11
samples but less than 75 percent data completeness shall be included in
the computation if the resulting spatially averaged annual mean
concentration (rounded according to the conventions of section 2.3 of
this appendix) is greater than the level of the standard.
(c) Situations may arise in which there are compelling reasons to
retain years containing quarters which do not meet the data completeness
requirement of 75 percent or the minimum number of 11 samples. The use
of less than complete data is subject to the approval of the appropriate
Regional Administrator.
(d) The equations for calculating the 3-year average annual mean of
the PM2.5 standard are given in section 2.5 of this appendix.
2.2 24-Hour PM2.5 Standard.
(a) The 24-hour PM2.5 standard is met when the 3-year
average of the 98th percentile values at each monitoring site
is less than or
[[Page 118]]
equal to 65 [micro]g/m\3\. This comparison shall be based on 3
consecutive, complete years of air quality data. A year meets data
completeness requirements when at least 75 percent of the scheduled
sampling days for each quarter have valid data. However, years with high
concentrations shall not be ignored just because they are comprised of
quarters with less than complete data. Thus, in computing the 3-year
average 98th percentile value, years containing quarters with
less than 75 percent data completeness shall be included in the
computation if the annual 98th percentile value (rounded
according to the conventions of section 2.3 of this appendix) is greater
than the level of the standard.
(b) Situations may arise in which there are compelling reasons to
retain years containing quarters which do not meet the data completeness
requirement. The use of less than complete data is subject to the
approval of the appropriate Regional Administrator.
(c) The equations for calculating the 3-year average of the annual
98th percentile values is given in section 2.6 of this
appendix.
2.3 Rounding Conventions. For the purposes of comparing calculated
values to the applicable level of the standard, it is necessary to round
the final results of the calculations described in sections 2.5 and 2.6
of this appendix. For the annual PM2.5 standard, the 3-year
average of the spatially averaged annual means shall be rounded to the
nearest 0.1 [micro]g/m\3\ (decimals 0.05 and greater are rounded up to
the next 0.1, and any decimal lower than 0.05 is rounded down to the
nearest 0.1). For the 24-hour PM2.5 standard, the 3-year
average of the annual 98th percentile values shall be rounded
to the nearest 1 [micro]g/m\3\ (decimals 0.5 and greater are rounded up
to nearest whole number, and any decimal lower than 0.5 is rounded down
to the nearest whole number).
2.4 Monitoring Considerations.
(a) Section 58.13 of this chapter specifies the required minimum
frequency of sampling for PM2.5. Exceptions to the specified
sampling frequencies, such as a reduced frequency during a season of
expected low concentrations, are subject to the approval of the
appropriate Regional Administrator. Section 58.14 of 40 CFR part 58 and
section 2.8 of appendix D of 40 CFR part 58, specify which monitors are
eligible for making comparisons with the PM standards. In determining a
spatial mean using two or more monitoring sites operating in a given
year, the annual mean for an individual site may be included in the
spatial mean if and only if the mean for that site meets the criterion
specified in Sec. 2.8 of appendix D of 40 CFR part 58. In the event
data from an otherwise eligible site is excluded from being averaged
with data from other sites on the basis of this criterion, then the 3-
year mean from that site shall be compared directly to the annual
standard.
(b) For the annual PM2.5 standard, when designated
monitors are located at the same site and are reporting PM2.5
values for the same time periods, and when spatial averaging has been
chosen, their concentrations shall be averaged before an area-wide
spatial average is calculated. Such monitors will then be considered as
one monitor.
2.5 Equations for the Annual PM2.5 Standard.
(a) An annual mean value for PM2.5 is determined by first
averaging the daily values of a calendar quarter:
Equation 1
[GRAPHIC] [TIFF OMITTED] TR18JY97.000
where:
xq,y,s = the mean for quarter q of year y for site s;
nq = the number of monitored values in the quarter; and
xi,q,y,s = the ith value in quarter q for year y
for site s.
(b) The following equation is then to be used for calculation of the
annual mean:
Equation 2
[GRAPHIC] [TIFF OMITTED] TR18JY97.001
where:
xy,s = the annual mean concentration for year y (y = 1, 2, or
3) and for site s; and
xq,y,s = the mean for quarter q of year y for site s.
(c)(1) The spatially averaged annual mean for year y is computed by
first calculating the annual mean for each site designated to be
included in a spatial average, xy,s, and then computing the
average of these values across sites:
Equation 3
[GRAPHIC] [TIFF OMITTED] TR18JY97.002
where:
xy = the spatially averaged mean for year y;
xy,s = the annual mean for year y and site s; and
ns = the number of sites designated to be averaged.
(2) In the event that an area designated for spatial averaging has
two or more sites at the same location producing data for the
[[Page 119]]
same time periods, the sites are averaged together before using Equation
3 by:
Equation 4
[GRAPHIC] [TIFF OMITTED] TR18JY97.003
where:
xy,s* = the annual mean for year y for the sites at the same
location (which will now be considered one site);
nc = the number of sites at the same location designated to
be included in the spatial average; and
xy,s = the annual mean for year y and site s.
(d) The 3-year average of the spatially averaged annual means is
calculated by using the following equation:
Equation 5
[GRAPHIC] [TIFF OMITTED] TR18JY97.004
where:
x = the 3-year average of the spatially averaged annual means; and
xy = the spatially averaged annual mean for year y.
Example 1--Area Designated for Spatial Averaging That Meets the Primary
Annual PM2.5 Standard.
a. In an area designated for spatial averaging, four designated
monitors recorded data in at least 1 year of a particular 3-year period.
Using Equations 1 and 2, the annual means for PM2.5 at each
site are calculated for each year. The following table can be created
from the results. Data completeness percentages for the quarter with the
fewest number of samples are also shown.
Table 1--Results from Equations 1 and 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Site Site Site Site
[bottom]1 [bottom]2 [bottom]3 [bottom]4 Spatial mean
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year 1......................................... Annual mean ([micro]g/m\3\)...... 12.7 ............ ............ ............ 12.7
% data completeness.............. 80 0 0 0 ............
Year 2......................................... Annual mean ([micro]g/m\3\)...... 12.6 17.5 15.2 ............ 15.05
% data completeness.............. 90 63 38 0 ............
Year 3......................................... Annual mean ([micro]g/m\3\)...... 12.5 18.5 14.1 16.9 15.50
% data completeness.............. 90 80 85 50 ............
3-year mean.................................... ................................. ............ ............ ............ ............ 14.42
--------------------------------------------------------------------------------------------------------------------------------------------------------
b. The data from these sites are averaged in the order described in
section 2.1 of this appendix. Note that the annual mean from site
3 in year 2 and the annual mean from site 4 in year 3
do not meet the 75 percent data completeness criteria. Assuming the 38
percent data completeness represents a quarter with fewer than 11
samples, site 3 in year 2 does not meet the minimum data
completeness requirement of 11 samples in each quarter. The site is
therefore excluded from the calculation of the spatial mean for year 2.
However, since the spatial mean for year 3 is above the level of the
standard and the minimum data requirement of 11 samples in each quarter
has been met, the annual mean from site 4 in year 3 is included
in the calculation of the spatial mean for year 3 and in the calculation
of the 3-year average. The 3-year average is rounded to 14.4 [micro]g/
m\3\, indicating that this area meets the annual PM2.5
standard.
Example 2--Area With Two Monitors at the Same Location That Meets the
Primary Annual PM2.5 Standard.
a. In an area designated for spatial averaging, six designated
monitors, with two monitors at the same location (5 and
6), recorded data in a particular 3-year period. Using
Equations 1 and 2, the annual means for PM2.5 are calculated
for each year. The following table can be created from the results.
Table 2--Results From Equations 1 and 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Average of
Site Site Site Site Site Site [bottom]5 Spatial
Annual mean ([micro]g/m\3\) [bottom]1 [bottom]2 [bottom]3 [bottom]4 [bottom]5 [bottom]6 and mean
[bottom]6
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year 1............................................ 12.9 9.9 12.6 11.1 14.5 14.6 14.55 12.21
Year 2............................................ 14.5 13.3 12.2 10.9 16.1 16.0 16.05 13.39
Year 3............................................ 14.4 12.4 11.5 9.7 12.3 12.1 12.20 12.04
3-Year mean....................................... ........... ........... ........... ........... ........... ........... .......... 12.55
--------------------------------------------------------------------------------------------------------------------------------------------------------
[[Page 120]]
b. The annual means for sites 5 and 6 are averaged
together using Equation 4 before the spatial average is calculated using
Equation 3 since they are in the same location. The 3-year mean is
rounded to 12.6 [micro]g/m\3\, indicating that this area meets the
annual PM2.5 standard.
Example 3--Area With a Single Monitor That Meets the Primary Annual
PM2.5 Standard.
a. Given data from a single monitor in an area, the calculations are
as follows. Using Equations 1 and 2, the annual means for
PM2.5 are calculated for each year. If the annual means are
10.28, 17.38, and 12.25 [micro]g/m\3\, then the 3-year mean is:
[GRAPHIC] [TIFF OMITTED] TR18JY97.005
b. This value is rounded to 13.3, indicating that this area meets
the annual PM2.5 standard.
2.6 Equations for the 24-Hour PM2.5 Standard.
(a) When the data for a particular site and year meet the data
completeness requirements in section 2.2 of this appendix, calculation
of the 98th percentile is accomplished by the following
steps. All the daily values from a particular site and year comprise a
series of values (x1, x2, x3, ...,
xn), that can be sorted into a series where each number is
equal to or larger than the preceding number (x[1],
x[2], x[3], ..., x[n]). In this case,
x[1] is the smallest number and x[n] is the
largest value. The 98th percentile is found from the sorted
series of daily values which is ordered from the lowest to the highest
number. Compute (0.98) x (n) as the number ``i.d'', where ``i'' is the
integer part of the result and ``d'' is the decimal part of the result.
The 98th percentile value for year y, P0.98, y, is
given by Equation 6:
Equation 6
[GRAPHIC] [TIFF OMITTED] TR18JY97.006
where:
P0.98,y = 98th percentile for year y;
x[i=1] = the (i=1)th number in the ordered series
of numbers; and
i = the integer part of the product of 0.98 and n.
(b) The 3-year average 98th percentile is then calculated
by averaging the annual 98th percentiles:
Equation 7
[GRAPHIC] [TIFF OMITTED] TR18JY97.007
(c) The 3-year average 98th percentile is rounded
according to the conventions in section 2.3 of this appendix before a
comparison with the standard is made.
Example 4--Ambient Monitoring Site With Every-Day Sampling That Meets
the Primary 24-Hour PM2.5 Standard.
a. In each year of a particular 3 year period, varying numbers of
daily PM2.5 values (e.g., 281, 304, and 296) out of a
possible 365 values were recorded at a particular site with the
following ranked values (in [micro]g/m\3\):
Table 3--Ordered Monitoring Data For 3 Years
----------------------------------------------------------------------------------------------------------------
Year 1 Year 2 Year 3
----------------------------------------------------------------------------------------------------------------
j rank Xj value j rank Xj value j rank Xj value
----------------------------------------------------------------------------------------------------------------
275 57.9 296 54.3 290 66.0
276 59.0 297 57.1 291 68.4
277 62.2 298 63.0 292 69.8
----------------------------------------------------------------------------------------------------------------
b. Using Equation 6, the 98th percentile values for each
year are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.008
[[Page 121]]
[GRAPHIC] [TIFF OMITTED] TR18JY97.009
[GRAPHIC] [TIFF OMITTED] TR18JY97.010
c.1. Using Equation 7, the 3-year average 98th percentile
is calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.011
2. Therefore, this site meets the 24-hour PM2.5 standard.
[62 FR 38755, July 18, 1997, as amended at 69 FR 45595, July 30, 2004]