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Atmospheric Carbon Dioxide Dry Air Mole Fractions from
the NOAA ESRL Carbon Cycle Cooperative Global Air Sampling
Network, 1968-2012
Version: 2013-08-28
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CONTENTS
1. Data source and contacts
2. Use of data
2.1 Citation
3. Reciprocity
4. Warnings
5. Update notes
6. Introduction
7. DATA - General Comments
7.1 DATA - Sampling Locations
7.2 DATA - File Name Description
7.3 DATA - Event with single parameter
7.4 DATA - Event with multiple parameters
7.5 DATA - QC Flags
7.6 DATA - Monthly Averages
8. Data retrieval
9. References
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1. DATA SOURCE AND CONTACTS
National Oceanic and Atmospheric Administration (NOAA)
Earth System Research Laboratory (ESRL)
Global Monitoring Division (GMD)
Carbon Cycle Greenhouse Gases (CCGG)
Correspondence concerning these data should be directed to:
Pieter P. Tans and Ed J. Dlugokencky
NOAA ESRL Global Monitoring Division
325 Broadway, GMD-1
Boulder, CO 80305
U.S.A.
email: Pieter.Tans@noaa.gov
Ed.Dlugokencky@noaa.gov
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2. USE OF DATA
These data are made freely available to the public and the
scientific community in the belief that their wide dissemination
will lead to greater understanding and new scientific insights.
The availability of these data does not constitute publication
of the data. NOAA relies on the ethics and integrity of the user to
insure that ESRL receives fair credit for their work. If the data
are obtained for potential use in a publication or presentation,
ESRL should be informed at the outset of the nature of this work.
If the ESRL data are essential to the work, or if an important
result or conclusion depends on the ESRL data, co-authorship
may be appropriate. This should be discussed at an early stage in
the work. Manuscripts using the ESRL data should be sent to ESRL
for review before they are submitted for publication so we can
insure that the quality and limitations of the data are accurately
represented.
2.1 CITATION
Please reference these data as
Dlugokencky, E.J., P.M. Lang, K.A. Masarie, A.M. Crotwell, and
M.J. Crotwell (2013), Atmospheric Carbon Dioxide Dry Air Mole
Fractions from the NOAA ESRL Carbon Cycle Cooperative Global Air
Sampling Network, 1968-2012, Version: 2013-08-28,
Path: ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/flask/surface/.
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3. RECIPROCITY
Use of these data implies an agreement to reciprocate.
Laboratories making similar measurements agree to make their
own data available to the general public and to the scientific
community in an equally complete and easily accessible form.
Modelers are encouraged to make available to the community,
upon request, their own tools used in the interpretation
of the ESRL data, namely well documented model code, transport
fields, and additional information necessary for other
scientists to repeat the work and to run modified versions.
Model availability includes collaborative support for new
users of the models.
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4. WARNINGS
Every effort is made to produce the most accurate and precise
measurements possible. However, we reserve the right to make
corrections to the data based on recalibration of standard gases
or for other reasons deemed scientifically justified.
We are not responsible for results and conclusions based on use
of these data without regard to this warning.
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5. UPDATE NOTES
+++++++++++++++++++++++++++++++
Lab-wide notes:
2011-10-07
We have introduced the term "measurement group", which identifies
the group within NOAA and INSTAAR that made the actual measurement.
We can now have multiple groups measuring some of the same trace
gas species in our discrete samples.
Measurement groups within NOAA and INSTAAR are
ccgg: NOAA Carbon Cycle Greenhouse Gases (CCGG)
hats: NOAA Halocarbons and other Atmospheric Trace Gases (HATS)
arl: INSTAAR Atmospheric Research Laboratory (ARL)
sil: INSTAAR Stable Isotope Laboratory (SIL)
curl: INSTAAR Laboratory for Radiocarbon Preparation and Research (CURL)
We have also changed the file naming convention (see section "DATA - FILE
NAME DESCRIPTION").
+++++++++++++++++++++++++++++++
Project-specific notes:
2013-08-27
Coordinates of some of the sample locations have changed.
These changes improve the specified location based on new
information. Changes tend to be minor and do not necessarily
reflect a change in the actual sampling location.
2011-10-01
The data file format has been modified to include the measurement group
and, additionally, the sample collection and analysis times now include
second information (e.g., 2011 03 15 23 06 12). See section 7.3 for
details.
2010-10-01
The format of the NOAA ESRL data records has been changed to include
an estimate of the uncertainty associated with each measurement. The
determination of the estimate is trace gas specific and described in
section 6 (INTRODUCTION).
+++++++++++++++++++++++++++++++
Parameter-specific notes:
2012-08-03
Corrections for drifting reference gas cylinders have been
applied to all samples measured on the following instruments
through the specified date.
Instrument ID Analysis Date
L3 thru 2009-10
L8 thru 2010-06
L10 thru 2010-10
2011-10-13
Discrete (flask) CO2 mole fractions from 1980 to 2006 have all
been recalculated to bring them into the WMO X2007 Mole Fraction
Scale (X07). The data since 2007 were already on the X07 scale.
WMO X2007 is based on repeated manometric measurements of the NOAA
primary standards (Zhao et al. 2006) and comparison of those results
to similar measurements made over a period of more than 10 years at
Scripps Institution of Oceanography. The difference between the X07
and the previous scales propagated by SIO and NOAA (X83, X87, etc.)
is ~0.2 ppm (X07-previous) in the 1980s, decreasing to ~0.1 ppm in
the late 1990s, and to 0.0 ppm by 2006. The recalculation of individual
measurements was accomplished by first determining the X07 values for
the reference gases used to measure the air samples and then using those
values with the raw data (NDIR voltages) to recompute mole fractions
for each sample.
1999-01-01
Corrections have been applied to CO2 mole fractions measured
on the flask analysis apparatus in use from July 1987 through
April 1998. The corrections are +0.1 ppm to samples measured
from July 1987 through 18 November 1993, and +0.24 ppm to samples
measured from 19 November 1993 through 10 April 1998.
Corrections for drifting reference gas cylinders have been
applied to all samples measured during 1995 through April 2008
on system L3 and 1998 through May 2007 on systems S2 and L3.
Files obtained previously from this site should be discarded and
replaced with the revised files contained in this version.
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6. INTRODUCTION
CO2 dry air mole fractions reported in these files were
measured by a nondispersive infrared absorption
technique in air samples collected in glass flasks at
NOAA ESRL Carbon Cycle Cooperative Global Air Sampling
Network sites. Descriptions of the sampling, measurement,
and calibration procedures are given in Komhyr et al.,
1983; Komhyr et al., 1985; Thoning et al., 1987, and
Thoning et al., 1995. Analysis and interpretation of
the data have been reported by Komhyr et al., 1985;
Conway et al., 1988; Tans et al., 1989a; Tans et al.,
1990, and Conway et al., 1994.
The file co2_flask_system.ps is a postscript file
explaining the operation of the flask analysis system used
from July 1987 through April 1998.
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7. DATA - GENERAL COMMENTS
Carbon dioxide (CO2) in ambient and standard air samples is
detected using a non-dispersive infrared (NDIR) analyzer.
The measurement of CO2 in air is made relative to standards
whose CO2 mole fraction is determined with high precision and
accuracy. Because detector response is non-linear in the range
of atmospheric levels, ambient samples are bracketed during
analysis by a set of reference standards used to calibrate
detector response. Measurements are reported in units of
micromol/mol (10^-6 mol CO2 per mol of dry air or parts per
million (ppm)). Measurements are directly traceable to the
WMO CO2 mole fraction scale.
Uncertainty in the measurements of CO2 from discrete samples
has not yet been fully evaluated. Key components of it are our
ability to propagate the WMO XCO2 scale to working standards,
the repeatability of the analyzers used for sample measurement,
and agreement between pairs of samples collected simultaneously.
Zhao and Tans (2006) determined that the internal consistency
of working standards is +/- 0.02 ppm (68% confidence interval).
The typical repeatability of the analyzers, based on repeated
measurements of natural air from a cylinder, is +/- 0.03 ppm.
Average pair agreement across the entire sampling network is
+/- 0.1 ppm.
The Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia) data have been merged and grouped into
5 degree latitude bins. For the South China Sea cruises (SCS) the
data are grouped in 3 degree latitude bins.
Sampling frequencies are approximately weekly for the fixed sites
and average one sample every 3 weeks per latitude zone for POC and
about one sample every week per latitude for SCS.
The air samples are collected by two general methods: flushing and
then pressurizing glass flasks with a pump, or opening a stopcock on
an evacuated glass flask. During each sampling event, a pair of
flasks is filled.
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7.1 DATA - SAMPLING LOCATIONS
Carbon Cycle Surface Flasks (ccg_surface).
The table includes the three letter code used to identify each
site; the site name; latitude, longitude, and elevation (meters
above sea level) of the sampling location; and country.
IMPORTANT NOTES:
1. Data for all species may not be available for all sites listed
in the table.
2. The exact location of a sampling site recorded in our database
may change or become better defined over time. The latitude,
longitude, and altitude of a sample event is based on the best
information available at the time of sample collection. Differences
in sample position associated with a particular site may be due
to the site moving or changes in technology that permit a more
accurate location determination.
To view near real-time data, manipulate and compare data, and create
custom graphs, please visit
http://www.esrl.noaa.gov/gmd/dv/iadv/.
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7.2 DATA - FILE NAME DESCRIPTION
Encoded into each file name are the parameter (trace gas identifier); sampling
site; sampling project; laboratory ID number; measurement group; and optional
qualifiers that further define the file contents.
All file names use the following naming scheme:
1 2 3 4 5 6
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt
1. [parameter]
Identifies the measured parameter or trace gas species.
(ex)
co2 Carbon dioxide
ch4 Methane
co2c13 d13C (co2)
merge more than one parameter
2. [site]
Identifies the sampling site code.
(ex)
brw
pocn30
car
amt
3. [project]
Identifies sampling platform and strategy.
(ex)
surface-flask
surface-pfp
surface-insitu
aircraft-pfp
aircraft-insitu
tower-insitu
4. [lab ID number]
A numeric field that identifies the measurement laboratory (1,2,3, ...).
NOAA ESRL is lab number 1 (see http://www.esrl.noaa.gov/gmd/ccgg/obspack/labinfo.html).
5. [measurement group]
Identifies the group with NOAA and INSTAAR that makes the actual measurement.
See Section 5 (UPDATE NOTES) for details.
(ex)
ccgg
hats
arl
sil
6. [optional qualifiers]
Optional qualifier(s) may indicate data subsetting or averaging.
Multiple qualifiers are delimited by an underscore (_). A more detailed
description of the file contents is included within each data file.
(ex)
event All measurement results for all collected samples (discrete (flask) data only).
hour_#### Computed hourly averages for the specified 4-digit year (quasi-continuous data only)
day Computed daily averages (quasi-continuous data only)
month Computed monthly mean values
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7.3 DATA - EVENT WITH SINGLE PARAMETER
The event data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/flask/surface/
use the following naming scheme (see Section 7.2):
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt
(ex) CH4_pocn30_surface-flask_1_ccgg.txt contains CH4 ccgg measurement
results for all surface flask samples collected on the Pacific
Ocean Cruise sampling platform and grouped at 30N +/- 2.5 degrees.
(ex) CO2_brw_surface-flask_1_ccgg.txt contains CO2 ccgg measurement
results for all surface flask samples collected at Barrow, Alaska.
The data files contain multiple lines of header information followed by one
record for each atmospheric measurement of a single parameter or trace gas species.
Fields are defined as follows:
Field 1: [SITE CODE] The three-character sampling location code (see above).
Field 2: [YEAR] The sample collection date and time in UTC.
Field 3: [MONTH]
Field 4: [DAY]
Field 5: [HOUR]
Field 6: [MINUTE]
Field 7: [SECOND]
Field 8: [FLASK ID] The sample container ID.
Field 9: [METHOD] A single-character code that identifies the sample
collection method. The codes are:
P - Sample collected using a portable, battery
powered pumping unit. Two flasks are
connected in series, flushed with air, and then
pressurized to 1.2 - 1.5 times ambient pressure.
D - Similar to P but the air passes through a
condenser cooled to about 5 deg C to partially
dry the sample.
G - Similar to D but with a gold-plated condenser.
T - Evacuated flask filled by opening an O-ring sealed
stopcock.
S - Flasks filled at NOAA ESRL observatories by sampling
air from the in situ CO2 measurement air intake system.
N - Before 1981, flasks filled using a hand-held
aspirator bulb. After 1981, flasks filled using a
pump different from those used in method P, D, or G.
F - Five liter evacuated flasks filled by opening a
ground glass, greased stopcock.
Field 10: [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).
Field 11: [MEASUREMENT GROUP] Identifies the group within NOAA and
INSTAAR making the actual measurement (e.g., ccgg, hats, arl).
See Section 5 (UPDATE NOTES) for details.
Field 12: [MEASURED VALUE] Dry air mole fraction or isotopic composition.
Missing values are denoted by -999.99[9].
Field 13: [ESTIMATED UNCERTAINTY] Estimated uncertainty of the reported
measurement value. Missing values are denoted by -999.99[9].
Field 14: [QC FLAG] A three-character field indicating the results of our
data rejection and selection process, described in section 7.5.
Field 15: [INSTRUMENT] A 2-character code that identifies the instrument
used for the measurement.
Field 16: [YEAR] The measurement date and time in LT.
Field 17: [MONTH]
Field 18: [DAY]
Field 19: [HOUR]
Field 20: [MINUTE]
Field 21: [SECOND]
Field 22: [LATITUDE] The latitude where the sample was collected, (negative (-)
numbers indicate samples collected in the southern hemipshere).
Field 23: [LONGITUDE] The longitude where the sample was collected, (negative (-)
numbers indicate samples collected in the western hemisphere).
Field 24: [ALTITUDE] The altitude where the sample was collected (masl).
Field 25: [EVENT NUMBER] A long integer that uniquely identifies the sampling
event.
Fields in each line are delimited by whitespace.
(ex)
SUM 2009 08 21 13 53 00 2145-99 P ch4 ccgg 1857.010 1.100 ... H11 2010 05 12 16 57 00 72.5800 -38.4800 3238.00 296091
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7.4 DATA - EVENT WITH MULTIPLE PARAMETERS
On special request we can distribute a "merged" file, which
includes for each sampling event, measurement results for muliple
parameters or trace gas species. A merged file does not include all
information found in a single parameter data file. For example,
merged files exclude measurement uncertainty, analysis instrument
ID and date and time for each parameter. Thus, the single parameter
data file is our most comprehensive data archive.
The format of a merged file is slightly different from single parameter event file.
A "merged" file will have the word "merge" in the parameter field of the file name.
The file name does not inform on the number of parameters included in the file.
Merged data files use the following naming scheme (see Section 7.2):
merge_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt
(ex) merge_pocn30_surface-flask_1_ccgg.txt contains ccgg measurement results for two or
more parameters for all surface flask samples collected on the Pacific Ocean Cruise
sampling platform and grouped at 30N +/- 2.5 degrees.
(ex) merge_brw_surface-flask_1_ccgg.txt contains ccgg measurement results for two or more
parameters for all surface flask samples collected at Barrow, Alaska.
The data files contain multiple lines of header information followed by one
record for each atmospheric measurement of a single parameter or trace gas species.
Fields are defined as follows:
Field 1: [SITE CODE] The three-character sampling location code (see above).
Field 2: [YEAR] The sample collection date and time in UTC.
Field 3: [MONTH]
Field 4: [DAY]
Field 5: [HOUR]
Field 6: [MINUTE]
Field 7: [SECOND]
Field 8: [FLASK ID] The sample container ID.
Field 9: [METHOD] A single-character code that identifies the sample
collection method. The codes are:
P - Sample collected using a portable, battery
powered pumping unit. Two flasks are
connected in series, flushed with air, and then
pressurized to 1.2 - 1.5 times ambient pressure.
D - Similar to P but the air passes through a
condenser cooled to about 5 deg C to partially
dry the sample.
G - Similar to D but with a gold-plated condenser.
T - Evacuated flask filled by opening an O-ring sealed
stopcock.
S - Flasks filled at NOAA ESRL observatories by sampling
air from the in situ CO2 measurement air intake system.
N - Before 1981, flasks filled using a hand-held
aspirator bulb. After 1981, flasks filled using a
pump different from those used in method P, D, or G.
F - Five liter evacuated flasks filled by opening a
ground glass, greased stopcock.
Field 10: [LATITUDE] The latitude where the sample was collected, (negative (-)
numbers indicate samples collected in the southern hemipshere).
Field 11: [LONGITUDE] The longitude where the sample was collected, (negative (-)
numbers indicate samples collected in the western hemisphere).
Field 12: [ALTITUDE] The altitude where the sample was collected (masl).
Field 13: [EVENT NUMBER] A long integer that uniquely identifies the sampling
event.
There is a group of 4 fields for each parameter and measurement group included in the
merge file.
Field ##+1: [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).
Field ##+2: [MEASUREMENT GROUP] Identifies the group within NOAA and
INSTAAR making the actual measurement (e.g., ccgg, hats, arl).
See Section 5 (UPDATE NOTES) for details.
Field ##+3: [MEASURED VALUE] Dry air mole fraction or isotopic composition.
Missing values are denoted by -999.99[9].
Field ##+4: [QC FLAG] A three-character field indicating the results of our
data rejection and selection process, described in section 7.5.
Fields in each line are delimited by whitespace.
(ex)
SGP 2002 04 02 21 15 00 551-91 D 36.6200 -97.4800 374.00 115605 co2 CCGG 378.870 -.. ch4 CCGG 1874.995 ...
co CCGG 163.800 ... h2 CCGG 496.350 ... n2o CCGG 319.380 ..P sf6 CCGG 5.130 ..P co2c13 SIL -8.477 +..
co2o18 SIL -0.271 ...
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7.5 QC FLAGS
NOAA ESRL uses a 3-column quality control flag where each column
is defined as follows:
column 1 REJECTION flag. An alphanumeric other
than a period (.) in the FIRST column indicates
a sample with obvious problems during collection
or analysis. This measurement should not be interpreted.
column 2 SELECTION flag. An alphanumeric other than a
period (.) in the SECOND column indicates a sample
that is likely valid but does not meet selection
criteria determined by the goals of a particular
investigation.
column 3 INFORMATION flag. An alphanumeric other than a period (.)
in the THIRD column provides additional information
about the collection or analysis of the sample.
WARNING: A "P" in the 3rd column of the QC flag indicates
the measurement result is preliminary and has not yet been
carefully examined by the PI. The "P" flag is removed once
the quality of the measurement has been determined.
Samples are collected in pairs, the pair
difference is calculated, and samples with
a pair difference greater than 0.5 ppm ("bad
pairs") are flagged. Through 1988 one or both
members of a bad pair were sometimes retained if
they fell within +/- 3 residual standard deviations
from a fitted curve. From 1989 to the present, both
members of bad pairs have been automatically
rejected. Retained and rejected flasks are
flagged as follows:
Flag Description
RETAINED ... (3 periods) good pair
(D <= 0.5 ppm)
..H high member of bad
pair; retained
..L low member of bad
pair; retained
..I sample has also been measured
by another lab as part of
an intercomparison experiment
SELECTED .X. flagged automatically as an outlier,
greater than 3 sigma from a fitted curve
.Z. flagged manually as an outlier
(this is necessary to prevent
distortion of the curve used for
automated data selection)
REJECTED +.. high member of bad
pair; rejected
-.. low member of bad
pair; rejected
*.. off scale or broken
flask; rejected
N.. rejected due to
error in sampling
or analysis
A.. rejected due to
error in analysis
T.. sample collected as
part of a methods
test; not used in
data analysis
The retained values comprise the data set that we feel
best represents the CO2 distribution in the remote,
well-mixed global troposphere. These are the values
we use to calculate long-term trends and interannual
and seasonal variations in our studies of the global
carbon cycle. It is possible, and even likely, that
some of the values flagged as not representative of
background conditions are valid measurements, but
represent poorly mixed air masses influenced by local
or regional anthropogenic sources or strong local
biospheric sources or sinks. Users of these data
should be aware that data selection is a difficult
but necessary aspect of the analysis and interpretation
of atmospheric trace gas data sets, and the specific
data selection scheme used may be determined by the
goals of a particular investigation.
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7.6 DATA - MONTHLY AVERAGES
The monthly data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/co2/flask/surface/
use the following naming scheme (see Section 7.2):
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_month.txt
(ex) CH4_pocn30_surface-flask_1_ccgg_month.txt contains CH4 ccgg monthly
mean values for all surface flask samples collected on the Pacific
Ocean Cruise sampling platform and grouped at 30N +/- 2.5 degrees.
(ex) CO2_brw_surface-flask_1_ccgg_month.txt contains CO2 ccgg monthly
mean values for all surface flask samples collected at Barrow, Alaska.
Monthly means are produced for each site by first averaging all
valid measurement results in the event file with a unique sample
date and time. Values are then extracted at weekly intervals from
a smooth curve (Thoning et al., 1989) fitted to the averaged data
and these weekly values are averaged for each month to give the
monthly means recorded in the files. Flagged data are excluded from the
curve fitting process. 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 3 or more consecutive months
without data, monthly means are not calculated for these months.
The data files contain multiple lines of header information
followed by one line for each available month.
Fields are defined as follows:
Field 1: [SITE CODE] The three-character sampling location code (see above).
Field 2: [YEAR] The sample collection year and month.
Field 3: [MONTH]
Field 4: [MEAN VALUE] Computed monthly mean value
In these files a monthly mean value of -999.99 denotes months where there
are insufficient data to calculate a monthly mean.
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8. DATA RETRIEVAL
To transfer all files in a directory, it is more efficient to
download the tar or zipped files.
To transfer a tar file, use the following steps from the ftp prompt:
1. ftp> binary ! set transfer mode to binary
2. ftp> get filename.tar.gz ! transfer the file
3. ftp> bye ! leave ftp
4. $ gunzip filename.tar.gz ! unzip your local copy
5. $ tar xvf filename.tar ! unpack the file
To transfer a zipped file, use the following steps from the ftp prompt:
1. ftp> binary ! set transfer mode to binary
2. ftp> get filename.zip ! transfer the file
3. ftp> bye ! leave ftp
4. $ unzip filename.zip ! uncompress your local copy
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9. REFERENCES
Conway, T.J., P.P. Tans, L.S. Waterman, K.W. Thoning,
D.R. Kitzis, K.A. Masarie, and N. Zhang, 1994, Evidence
for interannual variability of the carbon cycle from the
NOAA/CMDL global air sampling network, J. Geophys. Res.,99,
22831-22855.
Conway, T.J., P. Tans, L.S. Waterman, K.W. Thoning,
K.A. Masarie, and R.H. Gammon, 1988, Atmospheric
carbon dioxide measurements in the remote global
troposphere, 1981-1984, Tellus, 40B, 81-115.
Komhyr, W.D., L.S. Waterman, and W.R. Taylor, 1983,
Semiautomatic nondispersive infrared analyzer
apparatus for CO2 air sample analyses, J. Geophys.
Res., 88, 1315-1322.
Komhyr, W.D., R.H. Gammon, T.B. Harris, L.S. Waterman,
T.J. Conway, W.R. Taylor, and K.W. Thoning, 1985,
Global atmospheric CO2 distribution and variations
from 1968-1982 NOAA/GMCC CO2 flask sample data, J.
Geophys. Res., 90, 5567-5596.
Tans, P.P., T.J. Conway, and T. Nakazawa, 1989a,
Latitudinal distribution of the sources and sinks of
atmospheric carbon dioxide from surface observations
and an atmospheric transport model, J. Geophys. Res.,
94, 5151-5172.
Tans, P.P, K.W. Thoning, W.P. Elliott, and T.J. Conway,
1989b, Background atmospheric CO2 patterns from weekly
flask samples at Barrow, Alaska: Optimal signal recovery
and error esitmates, in NOAA Tech. Memo. (ERL ARL-173).
Environmental Research Laboratories, Boulder, CO, 131 pp.
Tans, P.P., I.Y. Fung, and T. Takahashi, 1990,
Observational constraints on the global atmospheric
CO2 budget, Science, 247, 1431-1438.
Thoning, K.W., P. Tans, T.J. Conway, and L.S.
Waterman, 1987, NOAA/GMCC calibrations of CO2-in-air
reference gases: 1979-1985. NOAA Tech. Memo. (ERL
ARL-150). Environmental Research Laboratories,
Boulder, CO, 63 pp.
Thoning, K.W., P.P. Tans, and W.D. Komhyr, 1989,
Atmospheric carbon dioxide at Mauna Loa Observatory
2. Analysis of the NOAA GMCC data, 1974-1985,
J. Geophys. Res., 94, 8549-8565.
Thoning, K.W., T.J. Conway, N. Zhang, and D. Kitzis, 1995,
Analysis system for measurement of CO2 mixing ratios in
flask air samples, J. Atmos. and Oceanic Tech., 12, 1349-1356.
Zhao, C., and P.P. Tans (2006), Estimating uncertainty of the
WMO Mole Fraction Scale for carbon dioxide in air, J. Geophys.
Res. 111, D08S09, doi: 10.1029/2005JD006003.
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