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Atmospheric Methane Dry Air Mole Fractions from the
NOAA ESRL GMD Carbon Cycle Surface Network
Version: 2016-10-14
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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
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:
Arlyn Andrews
NOAA ESRL Global Monitoring Division
325 Broadway, GMD-1
Boulder, CO 80305
U.S.A.
email: Arlyn.Andrews@noaa.gov
Ed.Dlugokencky@noaa.gov
Patricia.M.Lang@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
Andrews, A.E., E. Dlugokencky, and P.M. Lang (2008),
Methane Dry Air Mole Fractions from the NOAA ESRL
Surface Network using Programmable Flask Packages
(PFP), 1992-2008, Version: 2016-10-14.
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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
+++++++++++++++++++++++++++++++
Lab-wide notes:
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.
+++++++++++++++++++++++++++++++
Project-specific notes:
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.
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:
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5. UPDATE NOTES
2015-07-07
We updated and extended the WMO CH4 X2004 scale to X2004A.
Details are described on a dedicated web page:
http://www.esrl.noaa.gov/gmd/ccl/ch4_scale.html.
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6. INTRODUCTION
A "Programmable Flask Package" was developed in the early 1990s for
use in our aircraft project to collect vertical profiles of air
samples. These packages (PFPs) are analyzed on the same analytical
systems used for the CCGG's global cooperative air sampling network
samples to measure CO2, CH4, CO, H2, N2O, and SF6. Many of the PFPs
are also analzed by the HATS group by GCMS for a suite of CFCs, HFCs,
HCFCs, NMHCs, and a few other species.
As a quality control step, we began deploying PFPs at some surface
sites in 2006. Most of these sites are tall towers, where the PFP
measurements can be compared with continuous in situ measurements of
CO2 and CO. Samples are collected approximately daily from one of
the tower intakes.
All samples were analyzed for methane at NOAA ESRL in Boulder, Colorado
by gas chromatography with flame ionization detection, and each sample
aliquot was referenced to the NOAA 2004A methane standard scale (see
www.esrl.noaa.gov/gmd/ccl/ch4_scale.html; Dlugokencky et al., 2005)
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7. DATA - GENERAL COMMENTS
Ambient and standard air samples are injected into the gas
chromatograph (GC) with a sampling valve. Methane (CH4) is
separated from other sample constituents using packed columns
and detected using flame ionization (FID). This process is
highly automated for field and laboratory operations. Instrument
response of the sample must be compared to a standard of known
CH4 content. Measurements are reported in units of nanomol/mol
(10^-9 mol CH4 per mol of dry air (nmol/mol) or parts per billion
(ppb)) relative to the NOAA 2004A CH4 standard scale. Repeatability
of our measurements, based on repeated analysis of air from a
high-pressure cylinder, has ranged from 1 to 3 nmol/mol
over the period of our measurements. The absolute accuracy of our
scale is estimated at 0.2%, or about 3 nmol/mol.
Sampling frequencies are approximately daily.
The air samples are collected using an automated Programmable Flask
Package (PFP).
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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.
Note: Data for all species may not be available for all sites listed
in the table.
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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]
We provide some NOAA Global Monitoring Division measurements
in two unique file formats (netCDF and ASCII text).
(ex)
txt ASCII text file
nc netCDF4 file
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7.3 DATA - EVENT WITH SINGLE PARAMETER
The data files "ccg/ch4/flask/event/" use the following naming
scheme (see Section 7.2):
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt
(ex) CH4_lef_surface-pfp_1_ccgg.txt contains CH4 ccgg measurement
results for all surface pfp samples collected at Park Falls, Wisconsin.
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:
A - Sample collected using a Programmable Flask Package (PFP).
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 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)
AMT 2009 01 13 18 03 10 3079-08 A co2 CCGG 395.760 -999.990 ... L8 2009 01 28 05
42 00 45.0300 -68.6800 156.97 50.00 106.97 268444
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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_lef_surface-pfp_1_ccgg.txt contains ccgg measurement results for two or
more parameters for all surface pfp samples collected at Park Falls, Wisconsin.
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:
A - Sample collected using a Programmable Flask Package (PFP).
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).
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)
LEF 2006 11 08 19 06 25 3123-03 A 45.9451 -90.2732 715.98 472.00 243.98 225568
co2 CCGG 395.150 ... ch4 CCGG 1911.270 ...
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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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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
Tans, P.P. et al., Carbon Cycle (Group Report), Climate Monitoring
and Diagnostics Laboratory, No. 23, Summary Report 1994-1995,
Hoffman, D.J., J.T. Peterson and R.M. Rosson, eds, US Department
of Commerce, Boulder, Colorado, 1996.
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