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
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CO and associated 13C

     At the same sites (Niwot Ridge, Colorado and Montaa 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 Montaa 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 80C with a carrier gas of zero 
air. The detector temperature is set at 275C.

     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 Montaa 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 
Montaa de Oro samples is quoted based on the standard deviation of the average of multiple
samples, as it is for mixing ratio at MDO.
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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 80C with a ruthenium methanizer 
at 300C.  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.
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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,
Montaa 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 Montaa 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 Montaa 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 
Montaa 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 Montaa 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 (Montaa 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.

     On the cf-GC/IRMS, a working reference gas of pure of H2 from Oxygen Services Co. 
(Costa Mesa, CA) wa  assigned its value by comparison to H2 gas purchased from Oztech Gas
Co. with an assigned value of -165.3% versus V-SMOW. Our working gas standard for the 
cf-GC/IRMS instrument was thus assigned a value of -169.4% for H2 versus V-SMOW.
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