Aditional information on the measurements of CO, CO2, CH4, and associated carbon, oxygen, and hydrogen isotopes is presented below for each of the three gases. Submitted by Stanley C. Tyler (949-824-2685, styler@uci.edu) Department of Earth System Science, University of California, Irvine, CA 92697-3100 _________________________________________________________________ CO and associated 13C At the same sites (Niwot Ridge, Colorado and Montaña de Oro, California) where we collect air samples to analyze for CH4 data, we also measure CO mixing ratios and 13CO isotope ratios (e.g., Tyler et al., 1999; DB1022, CDIAC archives). Atmospheric CO mixing ratio measurements begin with the first dates of sample collection at Niwot Ridge and Montaña de Oro while measurements of d13C -CO begin in late 1999 (NWT) and early 2000 (MDO). Hydroxyl radicals (OH), the most important oxidizing agent in the atmosphere, react with CO rather quickly, giving a CO lifetime of the order of a few months, to produce CO2 [Levy, 1971; Logan et al., 1981; Levine et al., 1985]. Thus, knowledge of the sources and sinks of tropospheric CO is vital to understanding and quantifying the distribution of OH concentrations in the atmosphere. Admittedly, 14C and d18O-CO, which we do not currently measure, provide at least as much information as the d13C -CO data. However, the simultaneous measurements of CH4 and CO for mixing and 13C isotope ratio (as well as CO2 data which we also collect) help us to screen samples for outliers not representative of well-mixed background surface air. Site descriptions, sample collection procedures, and most mixing ratio and isotope ratio analytical techniques are described in our sample archives for atmospheric CH4, appearing as the abstch4.txt file in the CDIAC DB1022 data base. Small differences or additions relevant to the CO data are noted below. Mixing ratios of CO are measured at UC Irvine a Shimadzu model 14A GC with a model RGD2 reduction gas analyzer detector (Trace Analytical, Menlo Park, CA). The separation column is 6 ft. (1/8" o.d.) of molecular sieve 5A at 80°C with a carrier gas of zero air. The detector temperature is set at 275°C. Our mixing ratio working standards for CH4, CO, and CO2 analyses are based on the NOAA/CMDL reference scale for these gases and have been inter-compared with and calibrated to NOAA/CMDL reference standards [Lang et al., 1990; Novelli et al., 1991]. Our level of precision for measurements of CO are ~±1-3 ppb for CO (1.0 to 2.0% uncertainty around 133.5 ppb). At Niwot Ridge, where only one air sample is collected each date, the mixing ratio uncertainty quoted is based on the measurement precision. At Montaña de Oro, where paired samples (or sometimes multiple pairs of samples) are routinely collected, the measurement uncertainty quoted is the standard deviation of the average of 2 or more samples. (Technically a true standard deviation requires a larger sample size, but our s.d. values give one a sense of the spread in the data from multiple samples.) For d13CO analyses we used conventional dual inlet IRMS. In this method, air samples are processed using a combustion vacuum line -- a necessary step to separate CH4, CO and CO2 from other constituents of the air sample and to convert CH4 to CO2. For a description of this procedure see Tyler et al. [1999] and references therein. These samples are then measured on our Finnigan MAT model 252 IRMS instrument. Precision of measurement on clean dry CO2 gas standards is ±0.01% for d13C and ±0.05% for d18O. The reproducibility of d13C-CO measurements from ~200 liters each of replicate air samples, when all possible errors associated with differences in sample canisters, sample pumping, vacuum line processing, and isotope measurement are taken into account, is ±0.20%. As for the mixing ratio measurements, Niwot Ridge d13C-CO is quoted with an implied measurement error equal to the overall reproducibility of the final value based on tests of multiple aliquots of the sample air sample, i.e. ±0.20%. Conversely, the uncertainty in d13C-CO values of Montaña de Oro samples is quoted based on the standard deviation of the average of multiple samples, as it is for mixing ratio at MDO. _________________________________________________________________ CO2 and associated 13C and 18O At the same sites above where we collect air samples to analyze for CH4 and CO data, we also measure CO2 mixing and d13C and d18O isotope ratios (e.g., Tyler et al., 1999; DB1022, CDIAC archives). Atmospheric CO2 measurements of mixing and stable isotope ratio begin with January 1999 at both Niwot Ridge (NWT) and Montana de Oro while (MDO). Measurements of d13C in atmospheric CO2 have long been used to help interpret the global CO2 budget [e.g., Keeling, 1958 and 1961; Mook et al., 1983; Keeling et al., 1984; Quay et al., 1992; Tans et al., 1993], while d18O measurements in atmospheric CO2 have added an important component to the interpretation of CO2 fluxes more recently [e.g., Ciais et al., 1997; Flanagan et al., 1997; Miller et al., 1999]. The d13C of atmospheric CO2 is an indicator of either plant photosynthesis or air-sea exchange of CO2. This is because terrestrial plants preferentially fix 12C in photosynthesis, thereby leaving remaining CO2 relatively 13C heavy, while the dissolution and evaporation of CO2 to and from ocean waters is practically non-fractionating isotopically. In addition, the burning of fossil fuel has significantly increased the CO2 content of the atmosphere, with a corresponding decrease in the d13C signal toward more negative values. On the other hand, the d18O of atmospheric CO2 is a marker to constrain separately the gross uptake (photosynthesis) and release (respiration) of carbon by terrestrial biota. This is because CO2 can exchange an 18O atom with two isotopically distinct reservoirs, i.e., either evaporating leaf water during photosynthesis or soil moisture during respiration. However, the simultaneous measurements of CH4 and CO for mixing and 13C isotope ratio (as well as CO2 data which we also collect) help us to screen samples for outliers not representative of well-mixed background surface air. Site descriptions, sample collection procedures, and most mixing ratio and isotope ratio analytical techniques have been described in our sample archives for atmospheric CH4 appearing in the CDIAC database. Small differences or additions to these are noted below. At UC Irvine, CO2 mixing ratios from canister and cylinder samples are measured using a Hewlett Packard 5880A gas chromatograph (GC) with flame ionization detector (FID). The CO2 column is 8 ft. (1/8" dia.) of HayeSep D at 80°C with a ruthenium methanizer at 300°C. The carrier gas is nitrogen and sample loading and injection is done with a 6 port valve and sample loop swept by the carrier stream. Our mixing ratio working standards for CH4, CO, and CO2 analyses are based on the NOAA/CMDL reference scale for these gases and have been inter-compared with and calibrated to NOAA/CMDL reference standards [Lang et al., 1990; Novelli et al., 1991]. Our level of precision for measurements of CO2 are ~±3-4 ppm (~1% uncertainty around 342 ppm). At Niwot Ridge, where only one air sample is collected each date, the mixing ratio uncertainty quoted is based on the measurement precision. At Montana de Oro, where paired samples (or sometimes multiple pairs of samples) are routinely collected, the measurement uncertainty quoted is the standard deviation of the average of 2 or more samples. (Technically a true standard deviation requires a larger sample size, but our s. d. values give one a sense of the spread in the data from multiple samples.) For d13CO analyses we used conventional dual inlet IRMS. In this method, air samples are processed using a combustion vacuum line -- a necessary step to separate CH4, CO and CO2 from other constituents of the air sample and to convert CH4 to CO2. For a description of this procedure see Tyler et al. [1999] and references therein. These samples are then measured on our Finnigan MAT model 252 isotope ratio mass spectrometer. Precision of measurement on clean dry CO2 gas standards is ±0.01% for d13C and ±0.05% for d18O. The reproducibility of d13C-CO2 measurements from ~200 liters each of replicate air samples, when all possible errors associated with differences in sample canisters, sample pumping, vacuum line processing, and isotope measurement are taken into account, is ±0.05%. Similar to the mixing ratio measurements, Niwot Ridge d13C-CO2 and d18O-CO2 values are quoted with an implied measurement error equal to the overall reproducibility of the final value based on tests of multiple aliquots of the sample air sample, i.e. ±0.05% and ±0.20% respectively. Conversely, the uncertainty in d13C-CO2 and d18O-CO2 values of Montana de Oro samples is quoted based on the standard deviation of the average of multiple samples, as it is for mixing ratio at MDO. Our delta values for atmospheric CO2 take into account a small correction for the presence of atmospheric N2O (~10-3 relative to CO2) which is trapped along with CO2 following the method of [Friedli and Siegenthaler, 1988]. Our working CO2 isotope reference gas (NZME) on the dual inlet IRMS instrument is CO2 obtained from NIWA in New Zealand with value of -47.61% (13C/12C) and -16.72 (18O/16O) versus v-PDB and v-PDB-CO2 respectively. Another working gas purchased from Oztech Gas Co. (Dallas, TX) with assigned values of -39.78% and -25.78% versus v-PDB and v-PDB-CO2 respectively is routinely compared to it. Both gases have been inter-compared to two internationally recognized CO2 standards. NBS-19 (CaCO3) and IAEA-CO-9 (BaCO3) which have established values of 1.95% and -47.12% versus PDB, respectively, and values of -2.20% and -15.28% vs. v-PDB-CO2, respectively [Stichler, 1995]. Versus our NZME reference, clean dry CO2 gas standards made from these carbonates had measured values of 1.92% and -2.11% for NBS-19 and -47.18% and -15.45% for IAEA-CO-9. _________________________________________________________________ CH4 and associated 2H and 13C We report mixing ratios and dD and d13C measurements of atmospheric CH4 from air samples collected bi-weekly from fixed surface sites in the United States. Our fixed surface sites are located at the mid-continental site Niwot Ridge, CO (41 degrees N, 105 degrees W) and a Pacific coastal site receiving strong westerlies, Montaña de Oro, CA (35 degrees N, 121 degrees W). Data from multiyear approximately bi-weekly sampling provide information relating seasonal cycling of CH4 sources and sinks in background air, record long term trends in CH4 mixing and isotope ratio related to the atmospheric CH4 loading, and may indicate regional CH4 sources. Our continuous record of CH4 mixing ratio and d13C-CH4 from Niwot Ridge extends from 1995 to 2001 while that of Montaña de Oro extends from 1996 to 2001. A more recently initiated time series of measurements of dD-CH4 were begun during 1998 at Niwot Ridge and during 2000 at Montaña de Oro. We are archiving these data to make them available for modeling and advanced calculations by other atmospheric researchers. The air sample collections continue to the present time. We will archive these data as soon as is practicable in order to increase the value of the time series of measurements. Niwot Ridge, Colorado is part of the continental divide for North America with an altitude of approximately 3.75 km. The collection site itself is located at latitude 40 degrees N and longitude 105 degrees W, about 4 km southeast of Niwot Ridge at an altitude of approximately 3.15 km. It is situated on land owned by the Mountain Research Station (MRS) of the University of Colorado and used as a Long Term Ecological Research site by the National Science Foundation. Our site is about 1 km northwest of the MRS building and 40 km west of Boulder, Colorado. Air samples are collected at the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL) compressor shed and tower located at the site. Wind patterns at Niwot Ridge are dominated by westerlies (Barry [1973]; Haagenson [1979]) although at times upslope flow from the south or southeast transports air from the Denver metropolitan area (located about 70 km to the southeast) to the site [Hahn, 1981; Johnson and Toth, 1982]. In our study all samples were collected before noon in order to increase the likelihood of sampling when the prevailing wind was from the west. Samples taken in this manner have the best chance to represent well-mixed background air from over the western United States without interference from regional contamination. Our second air sampling site is located along the coast of California in Montaña de Oro State Park near San Luis Obispo (35 degrees N, 121 degrees W). This site is protected from the city of San Luis Obispo by low lying foothills forming a ridge running parallel to the coast. The city of Morro Bay is northeast of the site, while the Diablo Canyon nuclear power plant is about 2 km to the southeast. According to the California Energy Commission [1985], which compiled measurements at two wind stations near to the site, Diablo Canyon, CA (years 1967 to 1981) and Santa Maria, CA (years 1948 to 1978), average annual wind speeds were about 16.1 and 12.7 km/hr, respectively, at the two stations. Additional data given for Santa Maria indicates that the months from March to June exhibited the highest winds, although only 20% or so above the mean wind speed, while late afternoon to early evening hours exhibited nearly twice the wind speed found for other times of the day. Accordingly, our air samples from Montaña de Oro were collected in late afternoon or early evening during periods when prevailing winds were from the west or northwest. Sample Collection Procedures. Air samples were collected into either passivated aluminum high pressure cylinders (Niwot Ridge, CO) or electro-polished 32-L stainless steel canisters custom fabricated for our research group (Montaña de Oro, CA) depending on the logistics dictated by the sampling system and shipping requirements. In either case, the samples were pressurized using a compressor system which draws air through clean tubing and into the vessel after first passing through one or more drying tubes (magnesium perchlorate filled) located on the high pressure side of the compressor. 793 liters (STP) of sample air was collected into the cylinders using a RIX model SA-3 compressor operated by our collaborators (Ed Dlugokencky and Duane Kitzis) at NOAA/CMDL in Boulder, CO. Canisters were filled by members of our research group using a portable battery-operated piston pump (Model 415CDC30/12B, Thomas, Co., Sheboygan, WI). Details of the sampling procedure, including compressor cleaning, cylinder and canister conditioning, and drying tube preparation can be found in Tyler et al. [1999]. Mixing Ratio Analytical Procedures. At UC Irvine, CH4 mixing ratios from canister and cylinder samples were measured using a Hewlett Packard 5880A gas chromatograph (GC) with a 10-port valve, sample loop, pre-column, separation column, and pre-column backflush. The separation column was 5 ft. (1/8" o.d.) of molecular sieve 5A while the precolumn was 1 ft. (1/8" o.d.) of the same material. Both columns were run at 100 degrees C. Our mixing ratio working standards for CH4, CO, and CO2 analyses are based on the NOAA/CMDL reference scale for these gases and have been inter-compared with and calibrated to NOAA/CMDL reference standards [Lang et al., 1990]. Our level of precision for measurements of CH4 is +/-5 to 10 ppb for CH4 (0.25-0.50% uncertainty around 1903 ppb). Relative to the NIST scale, atmospheric CH4 mixing ratios measured using the NOAA/CMDL standards are 0.023 ppm lower. Isotope Ratio Analytical Procedures. For d13C-CH4 analyses we used conventional dual inlet IRMS. In this method, air samples are processed using a combustion vacuum line -- a necessary step to separate CH4, CO and CO2 from other constituents of the air sample and to convert CH4 to CO2. For a description of this procedure see Tyler et al. [1999] and references therein. These samples are then measured on our Finnigan MAT model 252 IRMS instrument. Precision of measurement on clean dry CO2 gas standards is +/-0.01% for d13C and +/-0.05% for d18O. The reproducibility of d13C measurements from ~200 liters each of replicate air samples, when all possible errors associated with differences in sample canisters, sample pumping, vacuum line processing, and isotope measurement are taken into account, is +/-0.05% for d13C of CH4. For dD-CH4 analyses we used our cf-GC/IRMS instrument (Finnigan Delta XL+) coupled to our custom-designed CH4 gas preconcentrator [Rice et al., 2001]. A pyrolysis oven converts CH4 to H2 after its separation from the air stream and before its detection by the mass spectrometer. Our precision of measurement is +/-1.3% for CH4 processed from ~63 ml of whole air. Isotope Ratio Reference Gases. Our working CO2 isotope reference gas on the dual i nlet IRMS instrument is designated as NZME CO2 and was obtained from NIWA in New Zealand with value of -47.61% (13C/12C) versus V-PDB. Another working gas purchased from Oztech Gas Co. (Dallas, TX) with assigned value of -39.78% versus V-PDB is routinely compared to it. Both gases have been inter-compared to two internationally recognized CO2 standards. NBS-19 (CaCO3) and IAEA-CO-9 (BaCO3) which have established values of 1.95% and -47.12% versus PDB and V-PDB-CO2, respectively [Stichler, 1995]. Versus our NZME reference, clean dry CO2 gas standards made from these carbonates had measured values of 1.92% for NBS-19 and -47.18% for IAEA-CO-9. 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