CIDC FTP Data
Greenhouse Gases IDC Data on FTP
Data Access
A Subset of Atmospheric Chemistry Records from Trends'93
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Readme Contents
Data Set Overview
Sponsor
Original Archive
Future Updates

The Data
Characteristics
Source

The Files
Format
Name and Directory Information
Companion Software

The Science
Theoretical Basis of Data
Processing Sequence and Algorithms
Scientific Potential of Data
Validation of Data

Contacts
Points of Contact

References

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Data Set Overview

Precise records of past and present atmospheric CO2, CH4 and N20 concentrations are critical to studies attempting to understand the effects these gases have on climate change. Researchers have attempted to determine past levels of the atmospheric gases by a variety of techniques, including direct measurments of trapped air in polar ice cores, indirect determinations from carbon isotopis in tree rings, analysis of spectroscopic data, and measurements of carbon and oxygen isotopic changes in carbon sediments in deep-ocean cores. The modern period of precise atmospheric measurments began during the International Geophysical Year (1958) with Keeling's (Scripps Institution of Oceanography) pioneering determinations at Mauna Loa, Hawaii and at the South Pole. Since that time the number of sites that measure atmospheric gases has grown to over sixty sites on both the land surface and ocean.

This readme describes Atmospheric Chemistry records and isotope temperature records aquired from the Carbon Dioxide Information Analysis Center (CDIAC) Trends'93: A Compendium of Data on Global Change. Trends'93 is part of CDIAC continuing effort to distribute, in an accessible format, scientific data critical to global-change issues.

This subset of the Trends'93 collection includes the following:

Historical CO2 and CH4 records from the Vostok and Siple Station ice core

Historical isotope temperature records from Vostok ice cores

Atmospheric CO2 records from sites in Scripps Institution of Oceanography (SIO) air sampling network

Atmospheric CO2 and CH4 records from sites in NOAA'S Climate Monitoring and Diagnostics Laboratory (CMDL) air sampling network

Atmospheric N2O records from the Atmospheric Lifetime Experiment (ALE) and the Global Atmospheric Gases Experiment (GAGE).

Readers may note that two apparently different systems of units have been used in presenting the atmospheric data. For data from ice cores and for some modern atmospheric records, levels are presented as concentrations in parts per million by volume (ppmv). For much of the modern data, values are given as mixing ratios, in parts per million or in parts per million by volume. These differences in unit designations reflect the preferences of the researchers who have contributed their respective data sets for inclusion in Trends '93. In the context of atmospheric concentration in parts per million by volume refers to the number of volumes of the particular gas (CO2, CH4 and N20) per million volumes of sample. In this same context, mixing ratio in parts per million is derived by dividing the number of moles of the particular gas (CO2, CH4 and N20) by the total number of moles in the sample and then multiplying the quotient by one million. Assuming that the volume of a gas is proportional to the number of moles contained within the volume (this assumption should be valid for a gas (CO2, CH4 and N20) in air under the conditions that atmospheric measurements are routinely carried out), we can expect that a gas (CO2, CH4 and N20) concentrations should be equivalent to the same gases mixing ratios. For all practical applications, therefore, users of this data should consider the terms concentration and mixing ratio to be interchangeable.

Sponsor
CDIAC, the original archiver of this data, and the Goddard DAAC acknowledges the support and efforts of the international science community in contributing this data. Additional efforts have been made to provide readers with assistance in properly citing these data. The following citations are to be used for each of the data sets listed below:

Historical CO2 records from the Vostok ice core

Cite as: Barnola, J.M., D. Raynaud, C. Lorius, and Y.S. Korotkevich.
1994. Historical CO2 record from the Vostok ice core.
pp. 7-10. In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and
F.W. Stoss (eds), Trends'93A: Compendium of Data on Global
Change. ORNL/CDIAC-65 Carbon Dioxide Information Analysis
Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A
Historical CH4 records from the Vostok ice cores
Cite as: Chappellaz, J.M. Barnola, D. Raynaud, Y.S. Korotkevich, and
C. Lorius. 1994. Historical CH4 record from the Vostok ice core.
pp. 229-232. In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and
F.W. Stoss (eds), Trends'93A: Compendium of Data on Global
Change. ORNL/CDIAC-65 Carbon Dioxide Information Analysis
Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A
Historical isotope temperature records from Vostok ice cores

Cite as: Jouzel, J., C. Lorius, J.R. Petit, N.I. Barkov, and V.M.
Kotlyakov. 1994. Vostok isotopic temperature record. pp. 590-602.
In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds),
Trends'93A: Compendium of Data on Global Change. ORNL/CDIAC-65
Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, Tenn., U.S.A
Historical CO2 records from the Siple Station ice core

Cite as: Neftel, A., H. Friedle, E. Moor, H. Lotscher, H. Oeschger,
U. Siegenthaler, and B. Stauffer. 1994. Historical CO2 record
from the Siple Station ice core. pp. 11-14. In T.A. Boden, D.P.
Kaiser, R.J. Sepanski, and F.W. Stoss (eds), Trends'93A:
Compendium of Data on Global Change. ORNL/CDIAC-65 Carbon
Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, Tenn., U.S.A
Historical CH4 records from the Siple Station ice core

Cite as: Stauffer, B., A. Neftel, G. Fischer, and H. Oeschger. 1994.
Historical CH4 record from the Siple Station ice core. pp. 251-254.
In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds),
Trends'93A: Compendium of Data on Global Change. ORNL/CDIAC-65
Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, Tenn., U.S.A
Atmospheric CO2 records from sites in Scripps Institution of Oceanography (SIO) air sampling network

Cite as: Keeling, C.D., and T.P. Whorf. 1994. Atmospheric CO2 records
from sites in the SIO air sampling network. pp. 1-28. In T.A.,
Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds.),
Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65.
Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, Tenn., U.S.A.
Atmospheric CO2 records from sites in NOAA'S Climate Monitoring and Diagnostics Laboratory (CMDL) air sampling network

Cite as: Conway, T.J., P.P. Tans, and L.S. Waterman. 1994. Atmospheric
CO2 records from sites in NOAA/CMDL air sampling network.
pp. 41-119. In T.A., Boden, D.P. Kaiser, R.J. Sepanski, and
F.W. Stoss (eds.), Trends '93: A Compendium of Data on Global
Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis
Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.
Atmospheric CH4 records from sites in NOAA'S Climate Monitoring and Diagnostics Laboratory (CMDL) air sampling network

Cite as: Dlugokencky, E.J., P.M. Lang, K.A. Masarie, and L.P. Steele 1994.
Atmospheric CH4 records from sites in the NOAA/CMDL air sampling
network. pp. 274-350. In T.A., Boden, D.P. Kaiser, R.J. Sepanski,
and F.W. Stoss (eds.), Trends '93: A Compendium of Data on Global
Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center,
Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.
Atmospheric N2O records from the Atmospheric Lifetime Experiment (ALE) and the Global Atmospheric Gases Experiment (GAGE)

Cite as: Prinn, R.G., R.F. Weiss, F.N. Alyea, D.M. Cunnold, P.J. Fraser,
P.G. Simmonds, A.J. Crawford, R.A. Rasmussen, and R.D. Rosen.
1994. Atmospheric N20 from the ALE/GAGE network. pp. 396-420.
In T.A., Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds.),
Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65.
Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, Oak Ridge, Tenn., U.S.A.

Original Archive
Trends: A Compendium of Data on Global Change is part of the Carbon Dioxide Information Analysis Center's (CDIAC's) continued effort to distribute, in an accessible format, scientific data critical to global-change issues. Trends is intended for researchers, policy makers, educators, and others interested in the observational data underlying the issues related to our changing global environment.

Trends presents historical and modern records of atmospheric concentrations of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), two chlorofluorocarbons (CFC-11 and CFC-12), a hydrochlorofluorocarbon (HCFC-22), and two halons (H-1301 and H-1211) from an expanded number of globally distributed sites. Virtually all of the modern records extend into the 1990s, some into 1994. Additional trace gas data presented in Trends include historical atmospheric CO2, CH4, and N2O records derived from ice cores. Trends also includes revised and updated estimates through 1991 for global, regional, and national CO2 emissions produced from the burning of fossil fuels, gas flaring, and the production of cement. Updated global emissions estimates through 1992 are also presented for CFC-11 and CFC-12. In addition, Trends updates and expands the presentation of long-term temperature records, whose spatial coverage ranges from an individual Antarctic (ice core) site to the entire globe and from the Earth's surface to the lower stratosphere. New subject matter appearing in Trends includes a chapter for long-term regional precipitation records, several time-series records for atmospheric aerosols, and isotopic 14C measurements for atmospheric CO2 from several sites.

Future Updates
Trends is a continuing series. The next issue of Trends will be Trends'95.

The Data

Characteristics
Parameters:
Atmospheric carbon dioxide (CO2) concentration and mixing ratio
Atmospheric methane (CH4) concentration and mixing ratio
Temperature Variation
Atmospheric nitrous oxide (N2O) concentration, and mixing ratio

Units:
CO2 concentration and mixing ratio
Parts Per Million (ppm) and Parts Per Million by Volume (ppmv)
Temperature variation
Degrees Celsius (C)
CH4 & N2O concentration and mixing ratio
Parts Per Billion (ppb) and Parts Per Billion by Volume (ppbv)

Range:
CO2 175 - 370
Vostok Temp -8.9 to 0.7
CH4 1530 - 1844
N2O 275 - 310

Temporal Coverage:
Historical Records
Vostok 164,000 - 1,700 BP
Sipple Station 1734 - 1983
SIO Network 1958 - 1993
NOAA/CMDL Network
CO2 Records 1968 - 1992
CH4 Records 1983 - 1992
N20 ALE & GAGE NETWORK
ALE 7/1978 - 5/1986
GAGE 12/1981 - 6/1994

Temporal Resolution:
All records are monthly except the Historical records from
Vostok and Siple which have varing temporal periods.

Spacial Coverage:
Historical CO2, CH4 and temperature records
2 station
SIO Network
4 stations
CO2 and CH4 Records from the NOAA/CMDL Network
35 fixed stations 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.)
N20 ALE & GAGE NETWORK
11 stations

Spatial Resolution:
Station Data or ship transit data. See individual data files
for latitudes and longitudes coordinates.

Source
Historical CO2 & CH4 Records From VOSTOK Ice Core

A record of atmospheric CO2 and CH4 concentrations for nearly 160,000 years was obtained by analyzing the air in bubbles trapped within a 2083-m-long ice core recovered by the Soviet Antarctic Expeditions at Vostok (East Antarctica).

Because air bubbles do not close at the surface of the ice sheet but only near the firn-ice transition (that is, at ~90 m below the surface at Vostok), the air extracted from the ice is younger than the surrounding ice (Barnola et al. 1991).

CO2:
Gas extraction and measurements were performed with the "Grenoble analytical setup," which involved crushing the ice sample under vacuum (in a stainless steel container) without melting it, expanding the gas released during the crushing into a pre-evacuated sampling loop, and then analyzing the CO2 concentrations by gas chromatography (Barnola et al. 1983). The analytical system, except for the stainless steel container in which the ice was crusshed, was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details concerning the Vostok CO2 record, see Barnola et al. (1987, 1991, 1994) and Lorius et al. (1985).

CH4:
Gas extraction and measurements involved melting the ice, in a glass vaccum aparatus (after removing the ambient air), then slowly refreezing the meltwater from the bottom pushing the air out of the ice water interface and passing it through an extraction line where it was measured with a gas chromatograph (GC). The GC was calibrated with a standard containing CH4 in a mixture of N2, O2, and CO2. For further details concerning the Vostok CH4 record, see Chappellaz et al. (1990, 1994), Raynaud et al. (1988), and Lorius et al. (1985).

Historical Temperature Records From VOSTOK Ice Cores

Because isotopic fractions of the heavier oxygen-18 and deuterium in snowfall are temperature dependent and a strong spatial correlation exist between the annual mean temperature and the mean isotopic ratio of precipitation, it is possible to derive ice-core climate records. The first isotopic analysis of the Vostok ice core was described in Lorius et al. (1985). This record presented by Jouzel et al. (1994) was the first ice core record to span a full glacial-interglacial cycle. Details on the methodology are presented in Jouzel et al. (1987, 1994) and Lorius et al. (1985).

Historical CO2 & CH4 Records From SIPLE Station Ice Core

Determinations of historical atmospheric CO2 concentrations for Siple Station, located in West Antarctica, were derived from measurements of air occluded in a 200-m core drilled at Siple Station in the Antarctic summer of 1983-84. The core was drilled by the Polar Ice Coring Office in Nebraska and the Physics Institute at the University of Bern. The ice could be dated with an accuracy of approximately 2 years to a depth of 144 m (which corresponds to the year 1834) by counting seasonal variations in electrical conductivity. Schwander and Stauffer (1984) reported a mean difference of 95 years between the age of the ice and the age of the air trapped in its bubbles. Below the 144 m depth, the core was dated by extrapolation (Friedli et al. 1986).

CO2:
The CO2 were extracted, from ice samples, by a dry-extraction system, in which bubbles were crushed mechanically to release the trapped gases, and then analyzed for CO2 by infrared laser absorption spectroscopy or by gas chromatography (Neftel et al. 1985). The analytical system was calibrated for each ice sample measurement with a standard mixture of CO2 in nitrogen and oxygen. For further details on the experimental and dating procedures, see Neftel et al. (1985, 1994), Friedli et al. (1986), and Schwander and Stauffer (1984).

CH4:
Measurements of CH4 in air from bubbles within the ice core were carried out through the use of two air extraction techniques. In one technique (vacuum melt extraction) ice samples (400 g) were melted in an evacuated glass container, and the escaping gas was then pumped into a small glass bulb continuously during the melting process. In the second technique (dry extraction) ice samples (600 g) were ground with a milling cutter in an evacuated steel container in order to mechanically release the ice core air from the opened bubbles. The excaping air was then collected in a small steel cylinder by condensation at 14 K. For both methods, CH4 measurements of the ice core air were made through the use of a Hewlett-Packard 5880A gas chromatograph. Two analyses were performed for each sample obtained by the melt extraction method, and three to four were performed for each sample obtained by the dry extraction method. Two gas mixtures composed of N2, O2, Ar, CO2, and CH4 were used as calibration standards for the analyses. Helium was used as a carrier gas. For further details on the extraction methods, ice dating, and standard gases, see Stauffer et al. (1985, 1994)

Atmospheric CO2 Records From Sites In the SIO Air Sampling Network

Methods-Mauna Loa:

Air samples at Mauna Loa are collected continuously from air intakes at the top of four 7-m towers and one 27-m tower. Four air samples are collected each hour for the purpose of determining the CO2 concentration. Determinations of CO2 are made by using an Applied Physics Corporation nondispersive infrared gas analyzer with a water vapor freeze trap. This analyzer registers the concentration of CO2 in a stream of air flowing at ~0.5 L/min. Every 20 minutes, the flow is replaced by a stream of calibrating gas or "working reference gas". In December 1983, CO2-in-N2 calibration gases were replaced with the currently used CO2-in-air calibration gases. These calibration gases and other reference gases are compared periodically to determine the instrument sensitivity and to check for possible contamination in the air- handling system. These reference gases are themselves calibrated against specific standard gases whose CO2 concentrations are determined manometrically. Greater details about the sampling methods at Mauna Loa are given in Keeling et al. (1982).

Hourly averages of atmospheric CO2, wind speed, and direction are plotted as a basis for selecting data for further processing. Data are selected for periods of steady hourly data to within ~0.5 parts per million by volume (ppmv); at least six consecutive hours of steady data are required to form a daily average. Greater details about the data selection criteria used at Mauna Loa are given in Bacastow et al. (1985).

Methods-Barrow:
Carbon dioxide was first measured at Barrow, Alaska, by Kelley and co-workers from the University of Washington during the 1960s through the use of a continuously operating analyzer. From January 1974 through February 1982, air samples were collected biweekly in triplicate 2-L evacuated glass flasks. Since March 1982, weekly air samples have been collected in 5-L evacuated glass flask pairs. Flasks are returned to the Scripps Institution of Oceanography (SIO) for CO2 determinations, which are made using an Applied Physics Corporation nondispersive infrared gas analyzer. In May 1983, the CO2- in-N2 calibration gases were replaced with the CO2-in-air calibration gases, which are currently used.

Methods-Samoa:
At Cape Matatula, Samoa, weekly air samples are collected in 5-L evacuated glass flasks exposed in triplicate. Flasks are returned to the SIO for CO2 determinations using an Applied Physics Corporation nondispersive infrared gas analyzer. In May 1983 the CO2-in-air calibration gases were replaced with CO2- in-air calibration gases, which are currently used.

Methods-South Pole:
Air samples are collected biweekly at the South Pole in 5-L evacuated glass flasks exposed as triplets. From 1957 until October 1963, 5-L glass flasks were exposed as singlets or pairs biweekly. Between 1960 and 1963, continuous in situ measurements of atmospheric CO2 concentrations were made. The data presented here are derived from both the flask sampling program and the continuous sampling program. Greater details about the sampling methods used at the South Pole are described in Keeling et al. (1976) and in Bacastow and Keeling (1981). Air samples collected at the South Pole are analyzed for CO2 concentration at SIO through the use of an Applied Physics Corporation nondispersive infrared gas analyzer with a water vapor freeze trap. In March 1983, CO2-in-air mixtures prepared by SIO replaced CO2-in-N2 as the calibration gases used to ascertain instrument sensitivity, detect possible contamination, and determine CO2 concentrations.

For air samples collected at Barrow, Samoa, and the South Pole to be considered indicative of uncontaminated background air, the replicate flask samples must agree within 0.40 parts per million by volume (ppmv).

Atmospheric CO2 and CH4 Records From Sites in the NOAA/CMDL Air Sampling Network

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.

Starting in 1968, air samples were collected in cylindrical glass flasks tapered at both ends to ground glass stopcocks lubricated with hydrocarbon grease. At several sites from 1980 to 1985 samples were also collected in spherical 5-L flasks equipped with a single ground glass stopcock. These flasks were filled by the evacuation method described below. In 1983, measurements of CH4 in the flask samples were begun. Experiments at this time revealed that CO2 mixing ratios increased with time in the greased flasks. In 1989, 0.5-L glass flasks equipped with glass piston Teflon O-ring stopcocks were introduced into the network so CO could be measured in addition to CO2 and CH4. In 1990, measurements of 13C/12C and 18O/16O of CO2 in the flask samples were begun. The precision of the isotopic measurements was better with larger volume flasks, so in 1991 2.5-L glass flasks with two Teflon O-ring stopcocks began to replace the 0.5-L flasks. In 1994, the conversion of the network to 2.5-L flasks will be completed.

Flasks samples are always collected in pairs, once or twice per week, on a schedule determined largely by the sample collector. The sample collectors have been given guidelines concerning preferred wind speeds, directions, and time of day for sample collection. Whole air samples are collected with no attempt to remove water vapor. Samples are dried during analysis using a cryogenic trap at -70 degree C.

From 1968 to 1980, collectors used a hand-held aspirator bulb to pull air through the flasks. In 1980, a portable battery powered pumping unit was introduced. This method allowed the sample collector to move downwind while the flasks, connected in series, were being flushed, enabled pressurization of the flasks, and incorporated an intake line that could be extended to 2 m above the ground. This device resulted in improved agreement between members of flask pairs and decreased scatter in the measurements. To avoid artifacts due to this inhomogeneity in the data quality, most CMDL analyses of the flask data begin with the 1981 data. The sampling method changed again in mid-1990 when an improved portable sampler was introduced. While the sampling principles were unchanged, the new sampler employed a single, larger battery; a more rugged, higher capacity pump; a 5-m intake line; and a back pressure regulator to control the pressure in the flasks. The effect of the flask and sampler improvements has been an increase in the percentage of sample pairs meeting a CO2 agreement criterion of 0.5 ppm, from ~75% in the mid-1980s to ~90% in 1992. However, overlapped sampling was conducted at several sites and no offsets due to the new flasks or sampling equipment were observed.

At Barrow (Alaska), Niwot Ridge (Colorado), Mauna Loa (Hawaii), Cape Kumukahi (Hawaii), Christmas Island, and Samoa, flask samples have also been collected in evacuated 3-L flasks. This type of flask is also used on the containerships making regular voyages in the Pacific Ocean between Los Angeles and New Zealand. In this method two flasks are filled in rapid succession by holding the flask into the wind, purging the dead volume in the inlet to the flask, opening the stopcock, and allowing the flask to fill with air to ambient atmospheric pressure. In overlapped sampling at Mauna Loa and Niwot Ridge, no significant difference was found between the 3-L flasks and the pressurized flasks. At Barrow and Cape Kumukahi, there is an indication of an offset of ~0.3 ppm, with the evacuated flasks generally being higher.

Descriptions of the sampling, measurement, and calibration procedures for the CO2 data are given in Komhyr et al., (1983, 1985) and Thoning et al., 1987. Analysis and interpretation of the CO2 data have been reported by Komhyr et al., 1985; Conway et al., 1988; Tans et al., 1989a; and Tans et al., 1990. Further explenation of the CH4 data are given in Lang et al. 1990a, 1990b, 1992, 1994; Steele et al. 1987, 1992.

Atmospheric N2O Records From ALE/GAGE Network

The Atmospheric Lifetime Experiment (ALE included measurements of several important trace gases. The experiment was designed to accurately determine the atmospheric concentration of these gases, so that their global circulation rates and globally averaged atospheric lifetimes could be calculated. Beginning in late 1981 at Cape Grim (Tasmania) and later at other site, additional measurments were collected using a new instrument as part of the Global Atmospheric Gases Experiment (GAGE). By mid-1986, ALE had ended and was succeded by GAGE at all site except the Adrigole (Ireland) station, which closed in December 1983 and was replaced by the GAGE station at Mace Head (Ireland) in January 1987.

The trace gas N20 has been extracted from the ALE/GAGE section in Trends93, to be included as part of the Goddard DAAC Inter Dicipline data colection.

Air samples, collected 4 times daily for ALE and 12 times daily for GAGE, where drawn in through an air intake located 2-15 m above the instrument building and were moved along a stainless steel line by a noncontaining metal bellows pump. The air was then filtered and dried to roughly 700 (ppmv) of H3O. Measurements of N2O were made from 2- or 3-mL air sample by using a 1.8-m x 6.4-mm isothermal (50 degree C) column packed with 80-100 mesh Porasil D.

The Files
Format
Name and Directory Information Naming Convention

The file naming convention for this data set is

ddddddd.pppp.ssss.ascii
where

ddddddd is the type of record
hist = Historical records from Vostok and Siple
cmdl = NOAA/CMDL air sampling network record
sio = SIO air sampling network record
alegage = ALE/GAGE network record
pppp is the parameter being measured
co2 = Carbon Dioxide
temp = Temperature
ch4 = Methane
n2o = Nitrous Oxide
ssss is the station name (the full name of each station is the
the header of the file)
ascii is the file format type

Directory Path

/data/atmo_constituents/greenhouse_gases

Companion Software
Read software is not provided since files are in simple Ascii text format.

The Science
Theoretical Basis Of Data

Carbon Dioxide:
Atmospheric Carbon Dioxide (CO2) provides a link between biological, physical, and anthropogenic processes. Carbon is exchanged between the atmosphere, the oceans, the terrestrial biosphere, and more slowly, with sediments and sedimentary rocks. In absence of anthropogenic CO2 inputs, the carbon cycle had periods of millennia in which large carbon exchanges were in near balance, implying nearly constant reservoir contents. Human activities have disturbed this balance through the use of fossil carbon and disruption of terrestrial ecosystems. The consequent accumulation of CO2 in the atmosphere has caused a number of carbon cycle exchanges to become unbalanced.

Methane & Nitrous Oxide:
Methane (CH4) is one of the most important radiatively active atmospheric trace gases, having the potential to affect climate significantly within the next century. A large body of evidence suggest that the concentration of CH4 in the atmosphere has risen rapidly in recent times and that present levels are perhaps twice as high as those of even a few hundred years ago in the pre-industrial era. The major methane sources are known to include entric fermentation in ruminant animals; anaerobic decay of organic matter in rice paddies, natural wetlands, and landfills; inadvertant release of trapped and adsorbed gas during coal mining, natural gas production and distribution, and oil exploration; and incomplete combustion during biomass burning. Knowledge of past and present atmospheric concentrations of CH4 and other trace gases is needed in order to elucidate the complex relationship between climate and ambient levels of greenhouse gases.

One of these other trace gases is nitrous oxide (N20), a gas whose atmospheric origin is not fully understood, but may result from a combination of human influences, including groundwater polution, use of nitrogen fertilizers, combustion, and deforestation.

Processing Sequence and Algorithms

CO2 CMDL Records:
The monthly CO2 data was produced as follows. First, both members of sample pairs are flagged when the CO2 difference between them is greater than 0.5 ppm. Prior to 1989, one value of a bad pair was sometimes retained, based on the result of the curve-fitting procedure described below. Since 1989, both members of bad pairs are automatically rejected. Samples that are affected by improper sampling techniques, or analytical problems are also flagged as rejected data. At this point a curve is fit to the remaining data, and values lying more that + or - 3 residual standard deviations from the curve are flagged as not representing well mixed, regionally representative air masses. The curve-fitting procedure is repeated until no more samples are flagged. The fitted curves are then used to calculate monthly and annual means. Most analysis of the NOAA/CMDL flask CO2 data use only the retained data, but the samples flagged as not representative of background conditions may still contain useful information.

For more detailed information on how monthly and annual means are calculated see Komhyr et al. (1985), Conway et al. (1988), and Conway et al. (1994).

CH4 CMDL Records:
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.

Scientific Potential of Data

These data can be used to study the increase of carbon dioxide, methane and nitrous oxide in the Earth's atmosphere and regional variations (Houghton et al., 1995; Sundquist, 1993). A major research field concerns the past and future effect of these gases on climate change and Global warming (Houghton et al., 1995; Cess et al., 1993; Hansen and Lacis 1990)

Validation of data

The various experiment teams took great care to ensure the accuracy and quality of their results in addition 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.

Contacts
Points of Contacts
For information about or assistance in using any DAAC data, contact

EOS Distributed Active Archive Center(DAAC)
Code 902.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771

Internet: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)

References


Bacastow, R.B., and C.D. Keeling. 1981. Atmospheric carbon dioxide concentration and the observed airborne fraction. pp. 103-12. In B. Bolin (ed.), Carbon Cycle Modelling, Scope 16. John Wiley and Sons, New York.

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