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Atmospheric Methane Dry Air Mole Fractions from
Quasi-continuous Measurements from the NOAA GML
Carbon Cycle Aircraft Program, 2020-2022.
Version: 2023-01-06
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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 - File Types
7.4 DATA - Content
7.5 DATA - QC Flags
7.6 DATA - Collection Methods
8. Data retrieval
9. References
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1. DATA SOURCE AND CONTACTS
National Oceanic and Atmospheric Administration (NOAA)
Global Monitoring Laboratory (GML)
Carbon Cycle Greenhouse Gases (CCGG)
Correspondence concerning these data should be directed to:
Kathryn McKain
NOAA Global Monitoring Laboratory
325 Broadway, GML-1
Boulder, CO 80305
U.S.A.
email: kathryn.mckain@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 see individual data files for citation text.
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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, modeled mole fractions, 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
+++++++++++++++++++++++++++++++
Project-specific notes:
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6. INTRODUCTION
These files contain quasi-continuous atmospheric measurements of dry air mole
fractions of methane collected from aircraft by the NOAA GML Carbon Cycle
Aircraft Program during short-term campaigns and at ongoing sites.
Flight tracks often include continuous ascending and descending vertical
profiling from the near-surface to higher altitudes. Vertical profile data
are useful for a variety of analyses in atmsopheric science, including
assessment of remote-sensing total-column retrievals, evalution of
vertical mixing and atmospheric transport, measurement of a set of values
that reflect shorter and longer space/time scales, and for quantification
of surface fluxes. When available, datasets will include a parameter which
identifies individual vertical profiles.
Contact NOAA GML for more specific information about individual datasets.
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7. DATA - GENERAL COMMENTS
7.1 DATA - SAMPLING LOCATIONS
For a summary of sampling locations, please visit
https://www.esrl.noaa.gov/gmd/ccgg/insitu/.
or https://gml.noaa.gov/ccgg/aircraft/.
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 DATA - 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.
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7.6 DATA - COLLECTION METHODS
Although the measurement setup has varied slightly for each campaign and
project due different requirements and constraints, there are common
methodological approaches which are typically utilized by the NOAA GML
Aircraft Program for insitu measurements (Karion et al. 2013). Aircraft
insitu measurements are made with the Picarro G2401-m cavity ring-down
spectrometer (Crosson 2008). Sample air is delivered to the analyzer
from an inlet that is mounted on the exterior of the aircraft via
1/8" stainless steel tubing and a pump located downstream of the
analyzer.
Mass flow for each analyzer and setup is typically ~150-200 sccm. Volume
flow varies with temperature and pressure. Reported measurement times
are corrected for lag time in the sample line. The native time resolution
of individual analyzers is typically between 2 and 4 seconds and may vary
slightly over time and among analyzers.
Sample air is typically not dried. Dry air mole fractions are computed
using analyzer-specific empirical corrections, derived from laboratory
tests performed before and after deployment to the field, that account
for dilution and pressure-broadening effects (Rella et al. 2013, Chen
et al. 2013). Repeated characterization of the water correction for
individual analyzers allows for uncertainty estimation of this term.
Analyzers are typically calibrated in the lab before and after each field
deployment against 6-7 tanks that cover a wide range of values. Calibration
tank values are assigned by the Central Calibration Laboratory at NOAA GML
(https://gml.noaa.gov/ccl/) and are traceable to World Meteorological
Organization (WMO) scales. One or two calibration cylinders is often flown
with the analyzer and measured before, during, and after each flight. When
available, in-flight calibration measurements are typically used to
derive a single offset correction for individual flights (Karion et al.
2013).
Reported uncertainties include consideration of uncertainty in the
water correction, lab and in-flight calibration, precision, and
uncertainty in values assinged to calibration tanks. If in-flight
calibrations are not available, repeated lab calibrations are used
estimate the uncertainty due to variability and drift in analyzer
response. Continuous measurement of tank air during flight has
also been used to investigate the sensitivity of the measurement
to changing conditions typically of flight conditions. When available,
comparison with independent measurements is also considered in the
uncertainty analysis.
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8. DATA RETRIEVAL
All (ASCII text and netCDF) files are located in
"https://gml.noaa.gov/aftp/data/trace_gases/ch4/pfp/aircraft/".
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
Chen H., A. Karion, C. W. Rella, J. Winderlich, C. Gerbig, A. Filges,
T. Newberger, C. Sweeney, P. P. Tans (2013) Accurate measurement of
carbon monoxide in humid air using the cavity ring-down spectroscopy
(CRDS) technique, Atmsopheric Measurement Techniques, 6, 4,
doi: 10.5194/amt-6-1031-2013.
Crosson E. R. (2008) A cavity ring-down analyzer for measuring
atmospheric levels of methane, carbon dioxide, and water vapor,
Applied Physics B, 92, doi: 10.1007/s00340-008-3135-y.
Karion A., C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. E. Andrews,
J. Kofler, D. Neff, P. Tans (2013) Long-term greenhouse gas measurements
from aircraft, Atmospheric Measurement Techniques, 6, 3,
doi: 10.5194/amt-6-511-2013.
Rella, C. W., H. Chen, A. E. Andrews, A. Filges, C. Gerbig, J. Hatakka, A. Karion,
N. L. Miles, S. J. Richardson, M. Steinbacher, C. Sweeney, B. Wastine, C. Zellweger
(2013) High accuracy measurements of dry mole fractions of carbon dioxide and
methane in humid air, Atmospheric Measurement Techniques, 6, 3,
doi: 10.5194/amt-6-837-2013.
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