This file describes the following data set: ATMOSPHERIC METHANE MIXING RATIOS--THE NOAA/CMDL GLOBAL COOPERATIVE AIR SAMPLING NETWORK, 1983-1993. CDIAC DB-1008 (1994) E.J. Dlugokencky, P.M. Lang, and K.A. Masarie, National Oceanic and Atmospheric Administration, Boulder, Colorado, U.S.A. L.P. Steele, Commonwealth Scientific and Industrial Research Organisation, Aspendale, Victoria, Australia CONTENTS I. Introduction II. Source and Scope of the Data III. Inventory of Sampling Sites IV. File Descriptions "*.ch4" (85 files -- each file presents all individual methane measurements at one NOAA/CMDL fixed monitoring site or one ocean vessel at one latitudinal site) "monthly.fxd" (file presents all monthly mean methane values for NOAA/CMDL fixed monitoring sites "monthly.shp" (file presents all monthly mean methane values for NOAA/CMDL shipboard sites) "sitemap.ps" (PostScript image file showing the location of sites in the NOAA/CMDL cooperative air sampling network) V. Data Checks Performed by CDIAC VI. References I. INTRODUCTION This data base presents atmospheric methane (CH4) mixing ratios from flask air samples collected over the period 1983-1993 by the National Oceanic and Atmospheric Administration, Climate Monitoring and Diagnostics Laboratory's (NOAA/CMDL's) global cooperative air sampling network. Air samples were collected approximately once per week at 44 fixed sites (37 of which were still active at the end of 1993). Samples were also collected at 5 degree latitude intervals along shipboard cruise tracks in the Pacific Ocean between North America and New Zealand (or Australia) and at 3 degree latitude intervals along cruise tracks in the South China Sea between Singapore and Hong Kong. The shipboard measurements were made approximately every 3 weeks per latitude zone by each of two ships in the Pacific Ocean and approximately once every week per latitude zone in the South China Sea. All samples were analyzed for CH4 at the NOAA/CMDL laboratory in Boulder, Colorado, U.S.A., by gas chromatography with flame ionization detection, and each aliquot was referenced to the NOAA/CMDL methane standard scale. In addition to providing the complete set of atmospheric CH4 measurements from flask air samples collected at the NOAA/CMDL network sites, this data base also includes files which list monthly mean mixing ratios derived from the individual flask air measurements. These monthly summary data are available for 35 of the fixed sites and 21 of the shipboard sampling sites. (Shipboard sites are actually 3 degree or 5 degree latitudinal bands. In the Pacific Ocean, samples were collected at a minimum of two different longitudes.) The data for the complete set of individual measurements are contained in 85 files, ranging in size from 2.7 kB to 187 kB and totaling 2.7 MB. Two additional files contain the monthly summary data. One of these files (30.2 kB) contains all monthly mean methane values for NOAA/CMDL fixed monitoring sites. The second file (14.3 kB) contains all monthly mean methane values for NOAA/CMDL shipboard sites. An additional file (151.0 kB) contains a PostScript image showing the locations of all fixed sampling sites in the NOAA/CMDL cooperative air sampling network; also shown are the approximate sampling locations from ocean vessels participating in the shipboard sampling program. The data and accompanying descriptive material are available in digitized form only; hardcopy documentation is not available. II. SOURCE AND SCOPE OF THE DATA Since its inception in 1968, the Climate Monitoring and Diagnostics Laboratory (CMDL) [known before 1989 as the Geophysical Monitoring for Climatic Change (GMCC) group] of the National Oceanic and Atmospheric Administration (NOAA) has developed a network of flask sampling sites for the analysis of atmospheric CO2 (Komhyr et al. 1985). Beginning on an experimental basis in April 1983, NOAA/CMDL expanded its flask sample analysis to include methane as well as CO2 (Lang et al. 1990a). The sampling network now includes 37 fixed sites, ranging in latitude from 82 degrees N to 90 degrees S (Lang et al. 1990b). Collection sites are typically located in remote areas to ensure that samples are representative of a large, well-mixed volume of the atmosphere (Steele et al. 1987). In 1986, the NOAA/CMDL cooperative air sampling network was expanded to include a program of shipboard measurements (Lang et al. 1992). Currently, methane data from shipboard sampling are available for 5 degree latitude intervals in the Pacific Ocean from two cruise vessels [Southland Star (PAC) and Wellington Star (PAW)] traveling between North America and New Zealand. Shipboard data are also available for 3 degree latitude intervals in the South China Sea (SCS) from two cruise vessels (Carla A. Hills and Great Promise) traveling between Singapore and Hong Kong. The earliest methane data from the NOAA/CMDL cooperative air sampling network are from January 1983, and come from three of the remote sites: Amsterdam Island, Halley Bay, and Palmer Station. (Collection began at these sites first, in anticipation of the long delay between sample collection and analysis in Boulder, Colorado.) Over the entire period 1983-1993, air samples were collected at 44 fixed sites, 37 of which were still active at the end of 1993. Seventeen sites contributed samples for one or more months of each year during 1983-1993. Twenty-three other sites began sampling at some time after 1983; of these, four were discontinued before 1993. Four other sites began sampling in 1983 but also were later discontinued. Detailed descriptions of sample collection, storage, and analysis methods are given in Steele et al. (1987, 1992), Lang et al. (1990a, 1990b, 1992, 1994), and Dlugokencky et al. (1994b). Brief summaries of these methods are given below. A variety of flask types and sample collection methods have been used in the NOAA/CMDL cooperative network. In the early years, most of the flasks used were 0.5-L cylindrical flasks fitted with two greased, ground-glass stopcocks. As time passed, 0.5-L cylindrical glass flasks fitted with two O-ring stopcocks were introduced. These 0.5-L flasks were prepared by first evacuating them (to check for leaks) and then filling them to slightly-greater-than-ambient pressure with dry gas (either air or nitrogen) containing a known amount of CO2 and methane. (CO2 was usually 20 ppm below ambient level and CH4 was undetectable: this makes it possible to tell if flasks were flushed properly before sampling.) Normally, collection involved connecting two flasks in series, flushing them with ambient air, and pressurizing them to 1.25-1.5 times ambient pressure through the use of a battery-powered suitcase sampler. Cylindrical 3-L glass flasks with a single O-ring stopcock have also been used on the ships and at sites where use of the battery-powered sampler was inconvenient or impractical. These flasks are evacuated and sent to the sampling sites. At the sampling sites, flasks are first purged repeatedly of the dead volume at the stopcock. The valve is then opened, the flask is allowed to fill with ambient air, and then the valve is closed. At the four NOAA observatories (South Pole, American Samoa, Mauna Loa, and Point Barrow) where continuous (i.e., in situ) monitoring of CO2 occurs, flasks are sometimes pressurized with the same pumping system used to supply air to the in situ CO2 analysis system (see Lang et al. 1990a). The sample collection interval was normally about 1 week at the fixed sites. At most sites, the sampling schedule was flexible, allowing samples to be taken under preferred conditions of wind direction and speed. For coastal sites, this usually entailed waiting for onshore winds with speeds greater than 4 m/s. In cases where the preferred conditions were not met within the 1-week interval, the sample would be taken regardless of conditions. For the shipboard sampling program, the sample collection interval was approximately 3 weeks per ship per latitude for the Pacific Ocean (PAC and PAW), and approximately 1 week per latitude for the South China Sea (SCS). Since May 1990, when Pacific Ocean air sampling by the cruise ship, Southland Star (PAC), was augmented by the contribution of a second ship, the Wellington Star (PAW), the overall frequency of sampling in the Pacific Ocean was increased because of the somewhat staggered schedules of the two ships. The time between sample collection and analysis usually ranged from several days to about 1 month. For some sites (e.g., Amsterdam Island and all Antarctic sites), the storage period averaged about 6 months, with some flasks being stored for more than one year. Methane mixing ratios were determined by gas chromatography using flame ionization detection. Before August 1985, analyses were performed on one of two Carle 211-M series S gas chromatographs (GCs). These were replaced by a Hach-Carle Series 400 (model 04270-A) GC. Details on the various integrators, computer interfaces, and accessories used with the GC systems are given in Steele et al. (1987), and Lang et al. (1990a, 1990b, 1992, 1994). Normally, only one member of a flask pair was analyzed for methane. Whenever possible, at least two aliquots were sampled from the selected flask to allow an estimation of the precision of the measurements. Each flask aliquot was bracketed by two aliquots of standard. The methane mixing ratio was calculated based on chromatographic peak heights from the equation: [CH4]samp = [CH4]std * (Hsamp/((Hstd1 + Hstd2)/2)), where [CH4]samp is the mixing ratio of methane in the sample, [CH4]std is the methane mixing ratio assigned to the calibration standard, Hsamp is the height of the methane peak in the sample, and Hstd1 and Hstd2 are the heights of the methane peaks in the two bracketing runs of the calibration standard. Calibration standards consisted of dry, natural air stored in high-pressure stainless steel or aluminum cylinders. During the entire 1983-1993 period, only five different tanks of calibration gas were used (see Lang et al. 1990a, 1990b, 1994; Steele et al. 1992). These calibration standards were regularly compared with standards obtained from various other sources, including the U.S. National Institute of Standards and Technology (formerly the National Bureau of Standards). To ensure that only those flask samples that were properly collected and analyzed would be included in the data set, all data and flask sampling information were examined for quality. Samples were occasionally rejected. In some cases, flask samples were found to be contaminated in a number of ways, including collection too close to a building (or even within a building), excessive exposure to sunlight, or collection when the wind direction was such that the wind brought air from a local source. In other cases, flasks were not adequately pressurized or not adequately flushed before pressurization. All measurements with obvious sampling or analytical problems, and those contaminated by localized sources of CH4, were flagged and excluded from further analysis. Further information regarding the problems encountered in flask sampling, and statistics pertaining to the number of flask samples rejected, are given in Lang et al. (1990a, 1990b, 1992, 1994). The monthly means are produced for each site by first averaging all values in the complete file with a unique sample date and time. These data are fit with a curve (see Steele et al., 1992 for curve fitting techniques), values are pulled from the curve at weekly intervals, and these values are averaged for each month to give the monthly mean values presented in the files. Some sites are excluded from the monthly mean directory, because sparse data or a short record does not allow a reasonable curve fit. Also, if there are three or more consecutive months without data, then these months are not included in the monthly mean file. Flagged data are excluded from the curve fitting process. III. INVENTORY OF SAMPLING SITES A. SITE DESCRIPTIONS AND RECORD PERIODS Site Period of code Site name and location Country Latitude Longitude Elev. record ALT Alert, N.W.T. Canada 82 27' N 62 31' W 210 1985-1993 AMS Amsterdam Island, Indian Ocean France 37 57' S 77 32' E 150 1983-1990 ASC Ascension Island, Atlantic Ocean U.K. 7 55' S 14 25' W 54 1983-1993 AVI St. Croix, Virgin Islands U.S.A. 17 45' N 64 45' W 3 1983-1990 AZR Terceira Island, Azores Portugal 38 45' N 27 05' W 30 1983-1993 BAL Baltic Sea Poland 55 30' N 16 40' E 7 1992-1993 BME St. David's head, Bermuda U.K. 32 22' N 64 39' W 30 1989-1993 BMW Southhampton, Bermuda U.K. 32 16' N 64 53' W 30 1989-1993 BRW Barrow, Alaska U.S.A. 71 19' N 156 36' W 11 1983-1993 CBA Cold Bay, Alaska U.S.A. 55 12' N 162 43' W 25 1983-1993 CGO Cape Grim, Tasmania Australia 40 41' S 144 41' E 94 1984-1993 CHR Christmas Island, Pacific Ocean Kiribati 1 42' N 157 10' W 3 1984-1993 CMO Cape Meares, Oregon U.S.A. 45 29' N 123 58' W 30 1983-1993 CRZ Crozet, Indian Ocean France 46 27' S 51 51' E 120 1991-1993 GMI Guam, Mariana Islands U.S.A. 13 26' N 144 47' E 2 1983-1993 HBA Halley Bay, Antarctica U.K. 75 40' S 25 30' W 10 1983-1993 ICE Heimaey, Vestmannaeyjar Iceland 63 15' N 20 09' W 100 1992-1993 ITN Grifton, North Carolina U.S.A. 35 21' N 77 23' W 505 1992-1993 IZO Tenerife, Canary Islands Spain 28 18' N 16 29' W 2300 1991-1993 KEY Key Biscayne, Florida U.S.A. 25 40' N 80 12' W 3 1983-1993 KPA Kitt Peak, Arizona U.S.A. 32 00' N 112 00' W 2083 1983-1989 KUM Cape Kumukahi, Hawaii U.S.A. 19 31' N 154 49' W 3 1983-1993 MBC Mould Bay, N.W.T. Canada 76 15' N 119 21' W 58 1983-1993 MCM McMurdo Station, Antarctica U.S.A. 77 50' S 166 36' E 11 1985-1987 MHT Mace Head, County Galway Ireland 53 20' N 9 54' W 25 1991-1993 MID Sand Island, Midway U.S.A. 28 13' N 177 22' W 4 1985-1993 MLO Mauna Loa, Hawaii U.S.A. 19 32' N 155 35' W 3397 1983-1993 NWR Niwot Ridge, Colorado U.S.A. 40 03' N 105 35' W 3475 1983-1993 NZL Kaitorete Spit New Zealand 43 50' S 172 38' E 3 1983-1985 OPW Olympic Peninsula, Washington U.S.A. 48 15' N 124 25' W 488 1984-1990 PAC Pacific Ocean (Southland Star) Blue Star L 5 degree lat. intervals 1986-1993 PAW Pacific Ocean (Wellington Star) Blue Star L 5 degree lat. intervals 1990-1993 PSA Palmer Station, Antarctica U.S.A. 64 55' S 64 00' W 10 1983-1993 QPC Qinghai Province P.R.C. 36 16' N 100 55' E 3810 1990-1993 RPB Ragged Point, St. Phillip's Parish Barbados 13 10' N 59 26' W 3 1987-1993 SCS South China Sea (Carla A. Hills) Chevron 3 degree lat. intervals 1991-1993 SCS South China Sea (Great Promise) NYK Shipping 3 degree lat. intervals 1993-1993 SEY Mahe Island Seychelles 4 40' S 55 10' E 3 1983-1993 SGI South Georgia Island, Atlantic Ocean U.K. 54 00' S 38 03' W 30 1989-1992 SHM Shemya Island, Alaska U.S.A. 52 43' N 174 06' E 40 1985-1993 SIO La Jolla, California U.S.A. 32 50' N 117 16' W 14 1984-1986 SMO Tutuila, American Samoa U.S.A. 14 15' S 170 34' W 42 1983-1993 SPO South Pole, Antarctica U.S.A. 89 59' S 24 48' W 2810 1983-1993 STM Ocean Station "M", North Atl. Ocean Norway 66 00' N 2 00' E 7 1983-1993 SYO Syowa Station, Antarctica Japan 69 00' S 39 35' E 11 1986-1993 TAP Tae-ahn Peninsula Korea 36 44' N 126 08' E 20 1990-1993 UTA Wendover, Utah U.S.A. 39 54' N 113 43' W 1320 1993-1993 UUM Ulaan Uul Mongolia 44 27' N 111 06' E 914 1992-1993 B. SPONSORING AGENCIES Site code Site name and location Country Sponsoring agency ALT Alert, N.W.T. Canada Environment Canada, AES AMS Amsterdam Island, Indian Ocean France Centre des Faibles Radioactivities/TAAF ASC Ascension Island, Atlantic Ocean U.K. U.S. Air Force & Pan Am. World Airways AVI St. Croix, Virgin Islands U.S.A. Fairleigh Dickinson University AZR Terceira Island, Azores Portugal U.S. Air Force (7th Weather Wing) BAL Baltic Sea Poland MIR, Sea Fisheries Inst. BME St. David's head, Bermuda U.K. Bermuda Biological Station (AEROCE) BMW Southhampton, Bermuda U.K. Bermuda Biological Station (AEROCE) BRW Barrow, Alaska U.S.A. NOAA/CMDL Observatory CBA Cold Bay, Alaska U.S.A. NOAA, U.S. National Weather Service CGO Cape Grim, Tasmania Australia CSIRO, Div. of Atmospheric Research CHR Christmas Island, Pacific Ocean Kiribati Scripps Inst. of Oceanography CMO Cape Meares, Oregon U.S.A. Oregon Graduate Inst. CRZ Crozet, Indian Ocean France Centre des Faibles Radioactivities/TAAF GMI Guam, Mariana Islands U.S.A. University of Guam, Marine Lab. HBA Halley Bay, Antarctica U.K. British Antarctic Survey ICE Vestmannaeyjar, Iceland Iceland Icelandic Meteorological Service ITN Grifton, North Carolina U.S.A. WITN Television IZO Tenerife, Canary Islands Spain Izana Observatory KEY Key Biscayne, Florida U.S.A. NOAA, Environmental Res. Lab. (AOML) KPA Kitt Peak, Arizona U.S.A. Battelle Pacific Northwest Lab. KUM Cape Kumukahi, Hawaii U.S.A. NOAA/CMDL Sampling Site MBC Mould Bay, N.W.T. Canada Environment Canada, AES MCM McMurdo Station, Antarctica U.S.A. U.S. Dept. of Defense MHT Mace Head, Count Galway Ireland Univ. College Atmos. Res. Sta. (AEROCE) MID Sand Island, Midway U.S.A. U.S. Navy MLO Mauna Loa, Hawaii U.S.A. NOAA/CMDL Observatory NWR Niwot Ridge, Colorado U.S.A. University of Colorado/INSTAAR NZL Kaitorete Spit New Zealand U.S. National Center for Atmos. Res. OPW Olympic Peninsula, Washington U.S.A. University of Washington PAC Pacific Ocean (Southland Star) Blue Star L Blue Star Line, Ltd. PAW Pacific Ocean (Wellington Star) Blue Star L Blue Star Line, Ltd. PSA Palmer Station, Antarctica U.S.A. National Science Foundation QPC Qinghai Province P.R.C. Chinese Academy of Meteorological Sci. RPB Ragged Point, St. Phillip's Parish Barbados University of Bristol SCS South China Sea (Carla A. Hills) Chevron Chevron Oil Co. SCS South China Sea (Great Promise) NYK Shipping Nippon Yusen Kaisha Shipping Co. SEY Mahe Island, Seychelles Seychelles New Mexico St. Univ., Phys. Sci. Lab. SGI South Georgia Island, Atlantic Ocean U.K. British Antarctic Survey SHM Shemya Island, Alaska U.S.A. U.S. Air Force SIO La Jolla, California U.S.A. Scripps Inst. of Oceanography SMO Tutuila, American Samoa U.S.A. NOAA/CMDL Observatory SPO South Pole, Antarctica U.S.A. NOAA/CMDL Observatory STM Ocean Station "M", North Atl. Ocean Norway Norway Meteorological Inst. TAP Tae-ahn Peninsula Korea Korea National Univ. of Education UTA Wendover, Utah U.S.A. U.S. National Weather Service UUM Ulaan Uul Mongolia Mongolian Hydrometeorolog. Res. Inst. IV. FILE DESCRIPTIONS "*.ch4" The data for the complete set of individual measurements are contained in 85 separate files, ranging in size from 2.7 kB to 187 kB and totaling 2.7 MB. Each file presents all individual methane measurements at one NOAA/CMDL fixed monitoring site or one ocean vessel at one latitudinal site. The record periods vary with site and are listed in the inventory of sampling sites (section III above). For each site, the data are ordered chronologically by sample date. Generally, the sample collection interval was approximately 1 week for fixed sites, approximately 1 week per latitude for shipboard sites in the South China Sea (SCS), and approximately 3 weeks per latitude per ship for shipboard sites in the Pacific Ocean (PAC and PAW). Data files for fixed sampling sites are named as "xxx.ch4", where xxx is the three-letter site code listed in the inventory of sampling sites. Data files for shipboard sites are named as "xxxhll.ch4", where xxx represents the ship (i.e., the "site code" given in the inventory of sampling sites), h represents the hemisphere (n=northern, s=southern, 0=equatorial), and ll the latitude in degrees. Latitudes are actually 3 degree bands (for SCS) or 5 degree bands (for PAC and PAW). For PAC and PAW, samples were collected at a minimum of two different longitudes within each latitudinal band. Each data record presents the following variables: site code, time of collection (year, month, day, hour, and minute), sample I.D. number, collection method code, methane mixing ratio, data selection code, instrument code, time of analysis (year, month, and day), raw file I.D., aliquot number of sample, and total number of aliquots analyzed. The file can be read by using the following FORTRAN code: C FORTRAN data retrieval routine to read the file named "*.ch4". C C Unit 1 is input. C CHARACTER SITE*3, ID*8, METHOD, SELECT*3, INSTR*2, RAWFILE*6 INTEGER COLLYR, COLLMO, COLLDA, COLLHR, COLLMN, ANALYR, ANALMO, 2 ANALDA, NTH, TOTAL REAL CH4 OPEN (UNIT=1, FILE='*.ch4') READ (1, 1) SITE, COLLYR, COLLMO, COLLDA, COLLHR, COLLMN, ID, 2 METHOD, CH4, SELECT, INSTR, ANALYR, ANALMO, ANALDA, 3 RAWFILE, NTH, TOTAL 1 FORMAT (/////////A3,1X,I4,1X,I2,1X,I2,1X,I2,1X,I2,1X,A8,1X,A1,2X, 2 F7.2,1X,A3,1X,A2,1X,I4,1X,I2,1X,I2,1X,A6,1X,I1,I1) 10 READ (1, 2, END=99) SITE, COLLYR, COLLMO, COLLDA, COLLHR, COLLMN, 2 ID, METHOD, CH4, SELECT, INSTR, ANALYR, 3 ANALMO, ANALDA, RAWFILE, NTH, TOTAL 2 FORMAT (A3,1X,I4,1X,I2,1X,I2,1X,I2,1X,I2,1X,A8,1X,A1,2X,F7.2,1X, 2 A3,1X,A2,1X,I4,1X,I2,1X,I2,1X,A6,1X,I1,I1) GO TO 10 99 STOP END The data can also be read by using the following SAS code: * SAS data retrieval routine to read the file named "*.ch4"; *; DATA COMPLETE; INFILE '*.ch4'; IF _N_=1 THEN INPUT ///////// SITE $ 1-3 COLLYR 5-8 COLLMO 10-11 COLLDA 13-14 COLLHR 16-17 COLLMN 19-20 @22 ID $CHAR8. METHOD $ 31 CH4 34-40 SELECT $ 42-44 INSTR $ 46-47 ANALYR 49-52 ANALMO 54-55 ANALDA 57-58 RAWFILE $ 60-65 NTH 67 TOTAL 68; ELSE INPUT SITE $ 1-3 COLLYR 5-8 COLLMO 10-11 COLLDA 13-14 COLLHR 16-17 COLLMN 19-20 @22 ID $CHAR8. METHOD $ 31 CH4 34-40 SELECT $ 42-44 INSTR $ 46-47 ANALYR 49-52 ANALMO 54-55 ANALDA 57-58 RAWFILE $ 60-65 NTH 67 TOTAL 68; RUN; Stated in tabular form, the contents include the following: __________________________________________________________ Variable Variable Starting Ending Variable type width column column __________________________________________________________ SITE Character 3 1 3 COLLYR Numeric 4 5 8 COLLMO Numeric 2 10 11 COLLDA Numeric 2 13 14 COLLHR Numeric 2 16 17 COLLMN Numeric 2 19 20 ID Character 8 22 29 METHOD Character 1 31 31 CH4 Numeric 7 34 40 SELECT Character 3 42 44 INSTR Character 2 46 47 ANALYR Numeric 4 49 52 ANALMO Numeric 2 54 55 ANALDA Numeric 2 57 58 RAWFILE Character 6 60 65 NTH Numeric 1 67 67 TOTAL Numeric 1 68 68 __________________________________________________________ where SITE is the three-letter site code given in the inventory of sampling sites (section III above). COLLYR is the year (Greenwich Mean Time) when the sample was collected. COLLMO is the month (Greenwich Mean Time) when the sample was collected. COLLDA is the day (Greenwich Mean Time) when the sample was collected. COLLHR is the hour (24-hr Greenwich Mean Time) when the sample was collected. Missing values are represented as 99. COLLMN is the minute (Greenwich Mean Time) when the sample was collected. Missing values are represented as 99. ID is the flask sample I.D. number. This field can contain up to eight characters but may contain fewer. This field may contain letters as well as numbers. NOTE: The sample date-time and flask ID number uniquely identify each sample. Details of the measurement strategy are given in Steele et al. 1987 and Lang et al. 1990a, 1990b, 1992, 1994. METHOD is a one-letter code that identifies the sample collection method. The codes are: P Samples were collected using a portable, battery powered pumping unit. Two flasks are connected in series, flushed with air, and then pressurized to 1.2 - 1.5 times ambient pressure. T Evacuated 3-L flasks were filled by opening an O-ring sealed stopcock. S Pairs of 0.5-L flasks were filled at NOAA/CMDL observatories by sampling air from the in situ CO2 measurement air intake system. N Pairs of 0.5-L flasks were filled using a pump different from those used in method P. F Five-liter evacuated flasks were filled by opening a ground glass, greased stopcock. CH4 is the methane mixing ratio, expressed in dry air parts per billion (1 X 10**9). Missing values are represented as -999.99. Values greater than or equal to 9999.99 ppb are represented as 9999.99. SELECT is a three-character flag indicating the results of NOAA/CMDL's data selection process. An alphanumeric other than a period (.) in the FIRST column indicates samples with obvious problems during sample collection or analysis. An alphanumeric other than a period (.) in the SECOND column indicates samples which are believed to be non-background. An alphanumeric other than a period (.) in the THIRD column is a sample qualifier that is not presently used. INSTR is a two-character code that identifies the instrument used for the CH4 measurement. The codes are: C1 Carle 211-M series S gas chromatograph (GC); Spectra- Physics (SP) 4100 integrator; Carle model 2026 8-port stream selection valve. C2 Carle 211-M series S GC; Hewlett-Packard (HP) 3390A and 3392A integrators; Carle Model 2026 8-port stream selection valve; HP 85-B computer (after October 1984). C3 Hach-Carle series 400 GC, model 04270-A; HP 3392A integrator; Hach-Carle Model 2026 8-port stream selection valve; HP 85-B computer. C4 Hach-Carle series 400 GC, basic model 04270-A, without a methanizer, but configured to backflush CO2 from the silica gel column; HP 3393A integrator and HP 310 workstation; Valco 4- and 8-port stream selection valves set up on a custom sample inlet system. C7 Hach-Carle series 400 GC, model 04270-A; HP 3393A integrator; Valco 4- and 8-port stream selection valves mounted on an automated sample inlet system. The sample loop of the Hach-Carle GC is connected in series with the sample loop of a second GC used for analysis of carbon monoxide and hydrogen; this dual GC system (including the sample inlet system) is controlled by a HP model 332 UNIX workstation. More detailed descriptions of the gas chromatographic systems used for CH4 analysis are given in Lang et al. 1990a, 1990b, 1992, and 1994. ANALYR is the year, in local time, of the CH4 analysis. ANALMO is the month, in local time, of the CH4 analysis. ANALDA is the day, in local time, of the CH4 analysis. RAWFILE is a six-character field identifying the raw file for this analysis date. NTH is the aliquot number of the sample whose measurement is presented. TOTAL is the total number of aliquots taken and measured from this flask. "monthly.fxd" This is a 30.2 kB data file containing all monthly mean methane mixing ratios for 35 NOAA/CMDL fixed monitoring sites, derived from flask measurements carried out approximately weekly over the period 1983-1993. Each data record presents three variables: site code, year, and atmospheric methane mixing ratio for each month of the year. The file can be read by using the following FORTRAN code: C FORTRAN data retrieval routine to read the file named "monthly.fxd". C C Unit 1 is input. C CHARACTER SITE*3 INTEGER YEAR, I REAL METH(12) OPEN (UNIT=1, FILE='monthly.fxd') READ (1, 1) SITE, YEAR, (METH(I), I=1,12) 1 FORMAT (/////////A3,1X,I4,12(1X,F7.2)) 10 READ (1, 2, END=99) SITE, YEAR, (METH(I), I=1,12) 2 FORMAT (A3,1X,I4,12(1X,F7.2)) GO TO 10 99 STOP END The data can also be read by using the following SAS code: * SAS data retrieval routine to read the file named "monthly.fxd"; *; DATA MON_FXD; INFILE 'monthly.fxd'; IF _N_=1 THEN INPUT ///////// SITE $ 1-3 YEAR 5-8 @10 (METH1-METH12) (7.2 +1); ELSE INPUT SITE $ 1-3 YEAR 5-8 @10 (METH1-METH12) (7.2 +1); RUN; Stated in tabular form, the contents include the following: __________________________________________________________ Variable Variable Starting Ending Variable type width column column __________________________________________________________ SITE Character 3 1 3 YEAR Numeric 4 5 8 METH1 Numeric 7 10 16 METH2 Numeric 7 18 24 METH3 Numeric 7 26 32 METH4 Numeric 7 34 40 METH5 Numeric 7 42 48 METH6 Numeric 7 50 56 METH7 Numeric 7 58 64 METH8 Numeric 7 66 72 METH9 Numeric 7 74 80 METH10 Numeric 7 82 88 METH11 Numeric 7 90 96 METH12 Numeric 7 98 104 __________________________________________________________ where SITE is the three-letter site code given in the inventory of sampling sites (section III above). YEAR is the year in which the air samples were collected. METH(1-12) are the monthly (1=January, 2=February, etc.) mean CH4 mixing ratios, expressed in dry air parts per billion (1 X 10**9). Missing values are represented as -999.99. "monthly.shp" This is a 14.3 kB data file containing all monthly mean methane mixing ratios for 21 NOAA/CMDL shipboard sites, derived from flask measurements carried out over the period 1986-1993. Shipboard sites are actually 3 degree latitudinal bands (for the South China Sea, SCS) or 5 degree latitudinal bands (for the Pacific Ocean, POC). In the Pacific Ocean, samples were collected at a minimum of two different longitudes within each latitudinal band. Monthly data for South China Sea latitudes were derived from flask air samples collected approximately once per week per latitude. For the Pacific Ocean, monthly data were derived from samples collected approximately once every three weeks per latitude. Initially, Pacific Ocean sampling was carried out by one cruise ship (PAC). Beginning in May 1990, the Pacific Ocean monthly data also incorporate measurements from air samples collected by a second cruise ship (PAW), whose sampling schedule was somewhat staggered with respect to that of PAC. Each data record presents five variables: site code, hemisphere, latitude, year, and atmospheric methane mixing ratio for each month of the year. The file can be read by using the following FORTRAN code: C FORTRAN data retrieval routine to read the file named "monthly.shp". C C Unit 1 is input. C CHARACTER SITE*3, HEMI INTEGER LAT, YEAR, I REAL METH(12) OPEN (UNIT=1, FILE='monthly.shp') READ (1, 1) SITE, HEMI, LAT, YEAR, (METH(I), I=1,12) 1 FORMAT (/////////A3,A1,I2,1X,I4,12(1X,F7.2)) 10 READ (1, 2, END=99) SITE, HEMI, LAT, YEAR, (METH(I), I=1,12) 2 FORMAT (A3,A1,I2,1X,I4,12(1X,F7.2)) GO TO 10 99 STOP END The data can also be read by using the following SAS code: * SAS data retrieval routine to read the file named "monthly.shp"; *; DATA MON_SHP; INFILE 'monthly.shp'; IF _N_=1 THEN INPUT ///////// SITE $ 1-3 HEMI $ 4 LAT 5-6 YEAR 8-11 @13 (METH1-METH12) (7.2 +1); ELSE INPUT SITE $ 1-3 HEMI $ 4 LAT 5-6 YEAR 8-11 @13 (METH1-METH12) (7.2 +1); RUN; Stated in tabular form, the contents include the following: __________________________________________________________ Variable Variable Starting Ending Variable type width column column __________________________________________________________ SITE Character 3 1 3 HEMI Character 1 4 4 LAT Numeric 2 5 6 YEAR Numeric 4 8 11 METH1 Numeric 7 13 19 METH2 Numeric 7 21 27 METH3 Numeric 7 29 35 METH4 Numeric 7 37 43 METH5 Numeric 7 45 51 METH6 Numeric 7 53 59 METH7 Numeric 7 61 67 METH8 Numeric 7 69 75 METH9 Numeric 7 77 83 METH10 Numeric 7 85 91 METH11 Numeric 7 93 99 METH12 Numeric 7 101 107 __________________________________________________________ where SITE is the three-letter site code. Values are either "POC" (denoting Pacific Ocean sites) or "SCS" (denoting South China Sea sites). HEMI is the hemisphere in which the samples were collected. Values are "n" (northern), "s" (southern), or "0" (equatorial). LAT is the latitude (in degrees) of the center of the band where air samples were collected. YEAR is the year in which the air samples were collected. METH(1-12) are the monthly (1=January, 2=February, etc.) mean CH4 mixing ratios, expressed in dry air parts per billion (1 X 10**9). Missing values are represented as -999.99. "sitemap.ps" This is a 151.0 kB black-and-white image file, which may be printed on any printer that supports PostScript language. The image consists of a world map showing the locations of all NOAA/CMDL global cooperative air sampling sites represented in this data base. The locations of the fixed sites are represented as large dots. The approximate locations of shipboard sampling sites are represented by small dots located along solid lines, which denote cruise tracks. V. DATA CHECKS PERFORMED BY CDIAC The Carbon Dioxide Information Analysis Center (CDIAC) endeavors to provide quality assurance (QA) of all data before their distribution. To ensure the highest possible quality in the data, CDIAC conducts extensive reviews for reasonableness, accuracy, completeness, and consistency of form. While having common objectives, the specific form of these reviews must be tailored to each data set; this tailoring process may involve considerable programming efforts. The entire QA process is an important part of CDIAC's effort to assure accurate, usable data for researchers. The following summarizes the QA checks performed on the NOAA/CMDL atmospheric methane data by CDIAC. 1. The format of all information was checked to ensure consistency throughout each data file. 2. All numeric values were inspected for reasonableness, logical consistency (e.g., no values of COLLYR <1983 or >1993; COLLMO or ANALMO <1 or >12; COLLDA or ANALDA <1 or >31; NTH or TOTAL <1), absence of typographical errors, and absence of outliers not accompanied by qualifying flag codes. No errors or inconsistencies of the types described above were found in the NOAA/CMDL atmospheric methane data and supporting documents received by CDIAC. The data files for the complete set of individual CH4 measurements are distributed by CDIAC in a form identical to that of the original files received from NOAA/CMDL. However, in order to enhance their ease of use, the monthly data received from NOAA/CMDL were reformatted in the following manner: 1. Files presenting monthly average mixing ratios for individual sites were concatenated into two files, "monthly.fxd" and "monthly.shp". Site identification was preserved by introducing an additional variable ("SITE") to each data record. 2. The files were reformatted to increase the number of monthly CH4 measurements for each line of data from one to 12 (i.e., from one month to an entire year). Months that reported missing values, which were simply omitted in the original files, are represented in the reformatted files by the missing value designation, -999.99. VI. REFERENCES Dlugokencky, E.J., J.M. Harris, Y.S. Chung, P.P. Tans, and I. Fung. 1993. The relationship between the methane seasonal cycle and regional sources and sinks at Tae-ahn Peninsula, Korea. Atmospheric Environment 27A(14):2115-20. Dlugokencky, E.J., K.A. Masarie, P.M. Lang, P.P. Tans, L.P. Steele, and E.G. Nisbet. 1994a. A dramatic decrease in the growth rate of atmospheric methane in the northern hemisphere during 1992. Geophysical Research Letters 21:45-48. Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. Masarie. 1994b. The growth rate and distribution of atmospheric methane. Journal of Geophysical Research 99:17,021-43. Ehhalt, D.H., P.J. Fraser, D. Albritton, R.J. Cicerone, M.A.K. Khalil, M. Legrand, Y. Makide, F.S. Rowland, L.P. Steele, and R. Zander. 1990. Trends in source gases. pp. 543-69. In Report of the International Ozone Trends Panel--1988. Global Ozone Research and Monitoring Project Report No. 18. World Meteorological Organization, Geneva. Fraser, P.J., M.A.K. Khalil, R.A. Rasmussen, and L.P. Steele. 1984. Tropospheric methane in the mid-latitudes of the Southern Hemisphere. Journal of Atmospheric Chemistry 1:125-35. Khalil, M.A.K., and R.A. Rasmussen. 1983. Sources, sinks, and seasonal cycles of atmospheric methane. Journal of Geophysical Research 88:5131-41. Khalil, M.A.K., and R.A. Rasmussen. 1990. Atmospheric methane: Recent global trends. Environmental Science and Technology 24:549-53. Komhyr, W.D., R.H. Gammon, T.B. Harris, L.S. Waterman, T.J. Conway, W.R. Taylor, and K.W. Thoning. 1985. Global atmospheric CO2 distribution and variations from 1968-82 NOAA/GMCC CO2 flask sample data. Journal of Geophysical Research 90:5567-96. Lang, P.M., L.P. Steele, R.C. Martin, and K.A. Masarie. 1990a. Atmospheric methane data for the period 1983-1985 from the NOAA/GMCC global cooperative flask sampling network. NOAA Technical Memorandum ERL CMDL-1. National Oceanic and Atmospheric Administration Environmental Research Laboratories, Boulder, Colorado, U.S.A. Lang, P.M., L.P. Steele, and R.C. Martin. 1990b. Atmospheric methane data for the period 1986-1988 from the NOAA/CMDL global cooperative flask sampling network. NOAA Technical Memorandum ERL CMDL-2. National Oceanic and Atmospheric Administration Environmental Research Laboratories, Boulder, Colorado, U.S.A. Lang, P.M., L.P. Steele, L.S. Waterman, R.C. Martin, K.A. Masarie, and E.J. Dlugokencky. 1992. NOAA/CMDL atmospheric methane data for the period 1983-1990 from shipboard flask sampling. NOAA Technical Memorandum ERL CMDL-4. National Oceanic and Atmospheric Administration Environmental Research Laboratories, Boulder, Colorado, U.S.A. Lang, P.M., E.J. Dlugokencky, K.A. Masarie, L.P. Steele. 1994. Atmospheric methane data for 1989-1992 from the NOAA/CMDL global cooperative air sampling network. NOAA Technical Memorandum ERL CMDL-7. National Oceanic and Atmospheric Administration Environmental Research Laboratories, Boulder, Colorado, U.S.A. Steele, L.P., P.J. Fraser, R.A. Rasmussen, M.A.K. Khalil, T.J. Conway, A.J. Crawford, R.H. Gammon, K.A. Masarie, and K.W. Thoning. 1987. The global distribution of methane in the troposphere. Journal of Atmospheric Chemistry 5:125-71. Steele, L.P., and P.M. Lang. 1991. Atmospheric methane concentrations--the NOAA/CMDL global cooperative flask sampling network, 1983-1988. ORNL/CDIAC-42, NDP-038. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A. Steele, L.P., E.J. Dlugokencky, P.M. Lang, P.P. Tans, R.C. Martin, and K.A. Masarie. 1992. Slowing down of the global accumulation of atmospheric methane during the 1980s. Nature 358:313-316. Tans, P.P., T.J. Conway, and T. Nakazawa. 1989. Latitudinal distribution of the sources and sinks of atmospheric carbon dioxide derived from surface observations and an atmospheric transport model. Journal of Geophysical Research 94:5151-72. Thoning, K.W., P.P. Tans, and W.D. Komhyr. 1989. Atmospheric carbon dioxide at Mauna Loa Observatory, 2, Analysis of the NOAA GMCC data, 1974-85. Journal of Geophysical Research 94:8549-65.