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[CIDC FTP Data]
[Greenhouse GasesIDC Data on FTP]
Data Access
A Subset of Atmospheric Chemistry Records from Trends'93
[rule]
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
[rule]
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
* File Size: range in size from 0.28 kB to 38 kB
* Data Format: Ascii tables
* Headers: Each file has a header containing information on the
station:
name,
latitudinal and longitudinal postition,
elevation of the station,
parameter and units measured, and
name of columns;
All columns in files, except historic ice core
records, are order as follows: the first column is
year, the next twelve columns are the months
beginning with January and ending with December,
the last column is an annual mean. The columns in
the historical ice core records are self
explaining.
* Delimiters: space
* Missing value: -99.9, -999.9 or -999.99
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/inter_disc/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)
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Last update:Fri Jul 18 11:58:07 EDT 1997
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