These data were produced by NOAA and are not subject to copyright protection in the United States. NOAA waives any potential copyright and related rights in these data worldwide through the Creative Commons Zero 1.0 Universal Public Domain Dedication (CC0 1.0)
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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 introduced the term "measurement group", which identifies
the group within NOAA or Institute of Arctic and Alpine Research (INSTAAR)
University of Colorado Boulder that made the 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 group (CCGG)
hats: NOAA Halocarbons and other Atmospheric Trace Species group (HATS)
arl: INSTAAR Atmospheric Research Laboratory (ARL)
sil: INSTAAR Stable Isotope Laboratory (SIL)
curl: INSTAAR Laboratory for Radiocarbon Preparation and Research (CURL)
+++++++++++++++++++++++++++++++
Project-specific notes:
2022-07-21
Dataset is now provided in self describing ObsPack format with improved metadata.
Surface flask event data are available in NetCDF and ASCII text. Surface flask
monthly data are available in ASCII text. Shipboard data binned by 5 or 3 degrees
are now removed from surface flask event data, but still provided in monthly data.
This format change makes some previous notes irrelevant.
+++++++++++++++++++++++++++++++
Parameter-specific notes:
2023-05-01
In Spring 2023, we moved to an internal quality control
(QC) tagging system for the flask air samples.
There are three categories of tags documenting
issues associated with sample collection, measurement
and representativity in the CCGG database.
Tags are more specific than flags, which allows
a more granular internal tracking and analysis of QC issues.
Tags are converted to simplified 3 character flags in the data
files for external data users. See section 7.5 for more details.
2021-02-08
CO2 measurements from flask-air samples were recalculated onto the
X2019 CO2 mole fraction scale by first reassigning all standards used
on the CO2 analysis sytems to X2019. CO2 values on X2019 from air
samples were caluclated by reprocessing the original raw files (i.e.,
files with raw analyzer output (typically voltages)) with the updated
assignments for the standards. A detailed description of the scale
revision from X2007 to X2019 is given in Hall et al. (2020), but the
main reasons were to correct biases caused by CO2 absorption by
O-rings in the manometric calibration system and to correct a virial
coefficient used in the calculation. The magnitiude of the differences
between X2019 and X2007 varies with CO2 abundance, and is typically
between 0.1 and 0.2 ppm. Some differences from the late-2000s and
early-2010s are larger (up to ~0.3 ppm) because of a mis-assigned
standard on the system used to transfer the scale to working standards.
Measurements prior to ~1980 from early analytical systems (instrument codes
LR1 and LR2) could not be reprocessed onto X2019; they remain on a CO2
scale originally developed at Scripps Institution of Oceanography.
2020-07-15
Based on comparison with in situ measurements at SPO and SYO
(from National Institute of Polar Research, Japan), a storage
correction was applied to flask-air samples measured for CO2.
The correction is ~0.2 ppm/yr at SPO and 0.08 ppm/yr at SYO.
Uncertainty for the correction has not yet been determined and
applied to the measurement uncertainty, but it is estimated to
be ~0.05 ppm.
2018-07-30
1. Uncertainties (68% c.i.) were estimated for all CO2
measurements. Uncertainity entries of -999.99 occur
when a reasonable uncertainty could not be calculated.
2. In 2017, began using N.. to flag samples not meeting
pair agreement criterion.
2016-07-07
We discovered a small leak in the intake line of the portable
sampler at Vestmannaeyjar, Iceland (ICE) that affected CO2.
All samples from 1 July 2009 through 28 June 2016 were
flagged N.. for CO2.
2012-08-03
Corrections for drifting standard 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 onto the WMO X2007 Mole Fraction
Scale (X2007). The data since 2007 were already on the X2007 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 X2007
and the previous scales propagated by SIO and NOAA (X83, X87, etc.)
is ~0.2 ppm (X2007-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 X2007 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
analyzer or cavity ring-down spectrometer (since Aug., 2019)
in air samples collected in glass flasks at
NOAA GML Carbon Cycle Cooperative Global Air Sampling
Network sites. Measurements are reported on the X2019 CO2
mole fraction scale. More information on this scale is available
here: https://gml.noaa.gov/ccl/co2_scale.html
Calibration procedures are given in
Komhyr et al., 1983; Komhyr et al., 1985; Thoning et al.,
1987, and Thoning et al., 1995; and Tans et al.,2017.
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.
Carbon dioxide (CO2) in ambient and standard air samples was
historically detected using a non-dispersive infrared (NDIR)
analyzer. The measurement of CO2 in air was made relative to
standards whose CO2 abundance was 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 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)).
In August, 2019, we switched from a NDIR to a Cavity Ring-Down
Spectrometer that analyzes CH4 and CO2. The analyzer response is
calibrated off-line with a suite of standards once per month
relative to a dry, natural reference air in a high-pressure
cylinder. All air samples are measured relative to the same reference,
and CH4 and CO2 values in measured samples are calculated based
on their ratio to the reference.
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7. DATA - GENERAL COMMENTS
Uncertainties of the CO2 measurements are included.
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 the long-term reproducibility.
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 high-pressure cylinder,
is +/- 0.06 ppm for NDIR and +/- 0.02 ppm for CRDS. Long-term
reproducibility is estimated to be +/- 0.03 ppm based on
repeated measurements of air from a high-pressure cylinder, or
the long-term variability in the differences between measurements
of test flasks on the flask-air analysis system and separate
measurements of the test gas used to fill the test flasks.
Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia) flask-air samples were collected in
about 5 degree latitude intervals. For South China Sea (SCS), samples
were collected at about 3 degree latitude intervals.
Sampling intervals are approximately weekly for fixed sites
and average one sample every 3 weeks per latitude zone for POC and
about one sample every week per latitude for SCS.
Historically, samples have been collected using two general methods:
flushing and then pressurizing glass flasks with a pump, or opening a
stopcock on an evacuated glass flask; since 28 April 2003, only the
former method is used. During each sampling event, a pair of flasks
is filled.
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7.1 DATA - SAMPLING LOCATIONS
For a summary of sampling locations, please visit
https://gml.noaa.gov/dv/site/?program=ccgg.
Note: Data for all species may not be available for all sites listed
in the table.
To view near real-time data, manipulate and compare data, and create
custom graphs, please visit
https://gml.noaa.gov/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 (optional); and optional
qualifiers that further define the file contents.
All file names use the following naming scheme:
1 2 3 4 5
[parameter]_[site]_[project]_[lab ID number]_[optional measurement group]_[optional
6 7
qualifiers].[file type]
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 sampling laboratory (1,2,3, ...).
NOAA GML is lab number 1 (see https://gml.noaa.gov/ccgg/obspack/labinfo.html).
5. [optional measurement group]
Identifies the group within the NOAA GML or the Institute of Arctic and Alpine
Research (INSTAAR) at the University of Colorado Boulder that made the
measurement.
It is possible to have multiple different 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 group (CCGG)
hats: NOAA Halocarbons and other Atmospheric Trace Species group (HATS)
arl: INSTAAR Atmospheric Research Laboratory (ARL)
sil: INSTAAR Stable Isotope Laboratory (SIL)
curl: INSTAAR Laboratory for Radiocarbon Preparation and Research (CURL)
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).
month Computed monthly averages all collected samples (discrete (flask) data only).
hour_#### Computed hourly averages for the specified 4-digit year (quasi-continuous data only)
HourlyData Computed hourly averages for entire record (quasi-continuous data only)
DailyData Computed daily averages for entire record (quasi-continuous data only)
MonthlyData Computed monthly averages for entire record (quasi-continuous data only)
7. [file type]
File format (netCDF, ASCII text).
(ex)
txt ASCII text file
nc netCDF4 file
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7.3 DATA - FILE TYPE
We now provide some NOAA Global Monitoring Laboratory measurements
in two unique file formats; netCDF and ASCII text.
The Network Common Data Form (NetCDF) is a self-describing, machine-independent
data format that supports creation, access, and sharing of array-oriented
scientific data. To learn more about netCDF and how to read netCDF
files, please visit http://www.unidata.ucar.edu.
The ASCII text (technically UTF-8 encoded) file is derived directly from the
netCDF file. The text file is also self-describing and can be viewed using
any ASCII or UTF-8 capable text editor. "Self-describing" means the file
includes enough information about the included data (called metadata)
that no additional file is required to understand the structure of the data
and how to read and use the data. Note that some non-ASCII characters (accents,
international character sets) may be present in various names and contact
information. These may require a UTF-8 capable text editor to view properly.
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7.4 DATA - CONTENT
See individual files for description of the provided variables and other
dataset metadata.
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7.5 QC FLAGS
Quality control 3-column flags indicate retained and rejected flask
results as follows in datafiles.
If the first character is not a period, the sample result should be
rejected for scientific use due to sample collection and/or measurement
issue. A second column character other than a period indicates a sample
that is likely valid but does not meet selection for representativeness
such as midday sampling or background air sampling. A third column flag
other than a period indicates abnormal circumstances that are not thought
to affect the data quality.
Flag Description
Retained ... good pair, no other issues
Rejected M.. sample measurement issue
C.. sample collection issue
B.. both measurement and collection issues
Selection .S. selection issue. High/low mole fraction
thought to not represent background
conditions for example.
Informational ..M informational measurement tag or
potential measurement issue
..C informational collection tag or
potential collection issue
The retained values comprise the data set that mostly represents
CO2 distribution in the remote, well-mixed global surface atmosphere.
Data with selection flag (with a 2nd column flag other than '.') are
likely valid measurements, but represent poorly mixed air parcels
influenced by local sources. Data selection is applied using a curve
fitting approach described in detail here:
https://gml.noaa.gov/ccgg/mbl/crvfit/crvfit.html
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7.6 COLLECTION METHODS
A single-character code is used to identify 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 GML 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
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7.7 DATA - MONTHLY AVERAGES
The monthly data files in https://gml.noaa.gov/aftp/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
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8. DATA RETRIEVAL
All (ASCII text and netCDF) files are located in
"https://gml.noaa.gov/aftp/data/trace_gases/co2/flask/surface/".
To transfer all files in a directory, it is more efficient to
download the tar or zipped files. Individual or zipped files can
be downloaded using your web browser by clicking the hyperlinked file
or right clicking hyperlink and using browser menu to 'save as' or similar.
Files can also be accessed by anonymous ftp at aftp.cmdl.noaa.gov.
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9. REFERENCES
Ballantyne, A. P., C. B. Alden, J. B. Miller,
P. Tans and J. W. C. White, (2012), Increase
in observed net carbon dioxide uptake by land and
oceans during the past 50 years, Nature, 488,
7409, , 10.1038/nature11299
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.
Tans, Pieter P., Andrew M. Crotwell and Kirk W. Thoning,
2017, Abundances of isotopologues and calibration of CO2
greenhouse gas measurements, Atmospheric Measurement
Techniques, 10, 7, 2669-2685, 10.5194/amt-10-2669-2017.
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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