---------------------------------------------------------------------
Atmospheric N2O Dry Air Mole Fractions from the
NOAA GML Carbon Cycle Cooperative Global Air
Sampling Network, 1997-2020
Version: 2021-07-30
--------------------------------------------------------------------
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 - File Types
7.4 DATA - Content
7.5 DATA - QC Flags
8. Data retrieval
9. References
--------------------------------------------------------------------
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
--------------------------------------------------------------------
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 (2021), Atmospheric Nitrous Oxide Dry Air Mole Fractions from the
NOAA GML Carbon Cycle Cooperative Global Air Sampling Network, 1997-2020,
Version: 2021-07-30, https://doi.org/10.15138/53g1-x417
--------------------------------------------------------------------
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.
--------------------------------------------------------------------
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.
--------------------------------------------------------------------
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:
2021-07-29
In 2020, the COVID-19 pandemic impacted flask shipping and sampling
frequency at many sites causing isolated gaps and some delayed
processing into the 2nd half of 2021. In spite of this, network
sampling coverage remained reasonably good throughout the year.
2021-07-28
In 2020, the covid-19 pandemic impacted flask shipping and sampling
frequency differently for different sites. For the most part
and thanks to everyone's efforts, the network sampling coverage
remained quite good in 2020.
Several sites still have samples from 2020 on site and they will be
analyzed once received.
2019-07-15
Surface flask event data is now provided in self describing NetCDF and ASCII text
formats with improved metadata. See section 7.3 for details.
We will provide a zip download of legacy text formatted files for a transitional period.
Monthly means data continues to be provided in text format.
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
2016-08-26
Latitude and longitude were adjusted for 3 sites:
ALT
Old: 82.4508 -62.5056 205.00 200.00
New: 82.4508 -62.5072 195.00 190.00
TAC
Old: 52.5178 1.1389 236.00 56.00
New: 52.5177 1.1386 236.00 56.00
ZEP
Old: 78.9067 11.8889 479.00 474.00
New: 78.9067 11.8883 479.00 474.00
Collaborator name corrected for UTA:
Old: U.S. National Weather Service [NWS]
New: Beth Anderson/NWS Cooperative Observer
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).
2015-08-03
The 3-letter site identification code for Ushuaia, Argentina (TDF) was
changed to USH to be consistent with the WMO GAWSIS.
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:
2018-07-30
Repeatability of ECD for N2O degraded in October, 2017,
and is reflected in the uncertainties.
--------------------------------------------------------------------
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.
-------------------------------------------------------------------
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).
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/.
-------------------------------------------------------------------
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 GML is lab number 1 (see http://www.esrl.noaa.gov/gmd/ccgg/obspack/labinfo.html).
5. [measurement group]
Identifies the group within NOAA GML 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
-------------------------------------------------------------------
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 file is derived directly from the netCDF file. The
text file is also self-describing and can be viewed using any 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.
-------------------------------------------------------------------
7.4 DATA - CONTENT
All (ASCII text and netCDF) files are located in
"ftp://aftp.cmdl.noaa.gov/data/trace_gases/n2o/flask/surface/".
Files are named as follows (see Section 7.2 for details):
n2o_[site]_surface-flask_1_ccgg_event.[file type]
-------------------------------------------------------------------
7.5 QC FLAGS
NOAA GML 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.
-------------------------------------------------------------------
8. DATA RETRIEVAL
Users may transfer individual files from a directory or may choose to
transfer a single zipped file. Zipped files contain the README file
and either netCDF files or ASCII text files depending on the zipped file
name.
(ex) n2o_mlo_surface-flask_1_ASCIItext.zip
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
-------------------------------------------------------------------
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.
-------------------------------------------------------------------