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Atmospheric N2O Dry Air Mole Fractions from the
NOAA GML Carbon Cycle Cooperative Global Air
Sampling Network, 1997-2019
Version: 2020-07-24
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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 Laboratories (ESRL)
Global Monitoring Laboratory (GML)
Carbon Cycle Greenhouse Gases (CCGG) Group
Correspondence concerning these data should be directed to:
Dr. Edward J. Dlugokencky
NOAA ESRL Global Monitoring Laboratory
325 Broadway, R/GML-1
Boulder, Colorado, 80305 USA
Telephone: 303 497-6228
Electronic Mail: 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
ensure that GML receives fair credit for their work. If the data
are obtained for potential use in a publication or presentation,
GML should be informed at the outset of the nature of this work.
If the GML data are essential to the work, or if an important
result or conclusion depends on the GML data, co-authorship
may be appropriate. This should be discussed at an early stage in
the work. Manuscripts using the GML data should be sent to GML
for review before they are submitted for publication so we can
ensure that the quality and limitations of the data are accurately
represented.
2.1 CITATION
Please reference these data as
Dlugokencky, E.J., A.M. Crotwell, J.W. Mund, M.J. Crotwell, and
K.W. Thoning (2020), Atmospheric Nitrous Oxide Dry Air Mole Fractions from the
NOAA GML Carbon Cycle Cooperative Global Air Sampling Network, 1997-2019,
Version: 2020-07, https://doi.org/10.15138/53g1-x417
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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 GML 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 introduced the term "measurement group", which identifies
the group within NOAA and 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)
We also changed the file naming convention (see section "DATA - FILE
NAME DESCRIPTION").
+++++++++++++++++++++++++++++++
Project-specific notes:
2020-07-16
Sample elevation was revised for ALT. All prior entries
were set to the correct elevation.
2019-09-09
Sample elevation was corrected for AMY. All prior entries
were set to the correct elevation.
2017-07-27
Method codes and sample locations were edited for accuracy.
Edited sites are: ZEP, BKT, OXK, CGO, RPB, ASC, CHR, ICE,
KEY, KUM, and TAP
2016-07-07
Incorrect sample dates from Ulaan Uul, Mogolia (UUM) from
20 Aug. 2013 through 30 Sept. 2015 were corrected on
13 May 2016.
2016-07-07
Since 24 Jan 2015, air samples from Negev Desert, Isreal (WIS)
are collected at 29.9731N, 35.0567E, 156 masl; the old location
was 30.8595N, 34.7809E, 482 masl.
2016-07-07
Since 03 Dec 2015, sampling in Natal, Brazil (NAT) was moved
from 5.5147S, 35.2603W, 20 masl to 5.7952S, 35.1853W, 87 masl.
2015-11-20
Updated the content and format of event files to include elevation in
meters above sea level (masl) and sample collection intake height in
meters above ground level (magl). Elevation plus collection intake
height equals altitude, which has always been included in the NOAA
distribution. In adding these 2 fields, the event number column
has moved. The new format is described in Sections 7.3 and 7.4.
Users may find minor changes (from earlier distributions) to reported
monthly mean values for the beginning months of data records. These
changes are due to minor corrections to our curve fitting methods as
first described by Thoning et al. (JGR, 1989).
2013-08-27
Coordinates of some of the sample locations were revised
to reflect improved information. Changes are minor.
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 seconds (e.g., 2011 03 15 23 06 12). See section 7.3
for details.
2010-10-01
The format of the NOAA GML 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:
2018-07-30
Repeatability of ECD for N2O degraded in October, 2017,
and is reflected in the uncertainties.
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6. INTRODUCTION
All samples were analyzed for N2O at NOAA ESRL in Boulder, Colorado
by gas chromatography with election capture detection or Tunable
Infrared Laser Direct Absorption Spectroscopy (since Aug., 2019),
and each sample aliquot was referenced to the NOAA 2006A N2O
standard scale (see Hall et al., 2007;
http://www.esrl.noaa.gov/gmd/ccl/n2o_scale.html).
The average repeatability has ranged from 0.02 to 0.4 ppb.
Data files in the subdirectories "ccg/n2o/flask/event" and
"ccg/n2o/flask/month" list N2O dry air mole fractions in nmol/mol
based on measurements from the NOAA GML Carbon Cycle Cooperative Global
Air Sampling Network. The subdirectory "event" contains all measurements
from air samples collected at each site and the subdirectory "month"
contains monthly means determined from the data files in "event". Network
sampling sites are listed in section 7.1.
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7. DATA - GENERAL COMMENTS
Aliquots of gas from ambient air samples and a cylinder of reference
gas are alternately injected into the gas chromatograph (GC) with a
sampling valve. Nitrous oxide (N2O) is separated from other sample
components using packed columns and detected with an electron
capture detector (ECD). The response of the ECD to N2O is calibrated
off-line about monthly relative to the reference with a suite of
standards. Each aliquot of sample is measured relative to the same
reference, and N2O values are calculated from the response function.
N2O measurements are reported in units of nanomol/mol (10^-9 mol N2O
per mol of dry air (nmol/mol) or parts per billion (ppb)) relative
to the NOAA 2006A N2O standard scale. Reproducibility of our
measurements (1 sigma), based on repeated analysis of air from a
high-pressure cylinder, is approximately 0.2 nmol/mol over the period
of our measurements.
In August, 2019, we replaced the GC/ECD method for N2O measurement with
a Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) method.
The analyzer is calibrated off-line once per month With a suite of
standards relative to a dry, natural air, reference in a high-pressure
cylinder. All air samples are measured relative the same reference,
and CH4 and CO2 values in measured samples are claculated based on
their ratio to the reference. Repeatability of the analyzer, based on
repeated analysis of air from a high-pressure cylinder, ranges from
~0.2 to 0.4 ppb for the GC to 0.02 ppb for the TILDAS analyzer (1 sigma).
The absolute accuracy of our standard scale is
estimated as +/-0.4 nmol/mol in the ambient atmospheric range of N2O
(95% confidence interval).
Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia) data were 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 intervals 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.
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
http://www.esrl.noaa.gov/gmd/dv/site/site_table.html.
IMPORTANT NOTES:
1. Data may not be available for all species at all sites listed
in the table.
2. The exact locations of a sampling sites 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
[parameter]_[site]_[project]_[lab ID number]_[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 ESRL is lab number 1 (see http://www.esrl.noaa.gov/gmd/ccgg/obspack/labinfo.html).
5. [measurement group]
Identifies the group within NOAA or 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).
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 - EVENT WITH SINGLE PARAMETER
The event data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/n2o/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 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.
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).
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 of the sample inlet (masl). The reported altitude
is the surface elevation plus sample intake height.
Field 25: [ELEVATION] Surface elevation (masl).
Field 26: [INTAKE HEIGHT] Air sample collection height above ground level (magl).
Field 27: [EVENT NUMBER] A long integer that uniquely identifies the sampling
event.
Fields in each line are delimited by whitespace.
(ex)
BRW 1971 10 19 01 20 00 48-71 N co2 CCGG 319.520 -999.990 N.. L1 1971 12 15 08 46
00 71.3200 -156.6000 13.00 11.00 2.00 26142
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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 a 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 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.
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 of the sample inlet (masl). The reported altitude
is the surface elevation plus sample intake height.
Field 13: [ELEVATION] Surface elevation (masl).
Field 14: [INTAKE HEIGHT] Air sample collection height above ground level (magl).
Field 15: [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).
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)
BRW 2015 11 02 20 05 00 4827-99 P 71.3230 -156.6114 16.00 11.00 5.00 397570
co2 CCGG 400.480 ... co CCGG 105.340 ...
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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 assessed.
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7.6 DATA - MONTHLY AVERAGES
The monthly data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/n2o/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
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
Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. Masarie, 1994, The growth
rate and distribution of atmospheric methane, J. Geophys. Res., 99, 17,021-
17,043.
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.
Hall, B. D., G. S. Dutton and J. W. Elkins (2007), The NOAA nitrous oxide
standard scale for atmospheric observations, Journal of Geophysical
Research-Atmospheres, 112, D09305, doi:10.1029/2006JD007954.
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