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Atmospheric Non Methane Hydrocarbons Mole Fractions
from the NOAA GML Carbon Cycle Surface Network
Version: 2021-05-04
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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)
Global Monitoring Laboratory (GML)
Carbon Cycle Greenhouse Gases (CCGG)
University of Colorado
Institute of Arctic and Alpine Research (INSTAAR)
Atmospheric Research Laboratory group (ARL)
Correspondence concerning these data should be directed to:
John Mund
NOAA Global Monitoring Laboratory
325 Broadway, R/GML-1
Boulder, CO 80305
U.S.A.
email: John.Mund@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
Helmig, D., Hueber, J., Tans, P., University Of Colorado Institute Of Arctic
And Alpine Research (INSTAAR), & NOAA GML CCGG Group. (2021). University of
Colorado Institute of Arctic and Alpine Research (INSTAAR) Flask-Air Sample
Measurements of Atmospheric Non Methane Hydrocarbons Mole Fractions from the
NOAA GML Carbon Cycle Surface Network at Global and Regional Background Sites,
2004-2016 (Version 2021.05.04) [Data set]. NOAA Global Monitoring Laboratory.
https://doi.org/10.15138/6AV8-GS57
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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:
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.
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:
2021-05-03
Several analysis dates were determined to be in error with data to
correct currently unavailable. These dates have been reset to the
sample date and time which should be interpreted as meaning that
the analysis date is unavailable. This should not impact data
quality in other ways as in-depth storage studies did not find
a notable influence of the time that has passed between sampling
and analysis.
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6. INTRODUCTION
All samples in this archive were analyzed for light hydrocarbons at INSTAAR,
Atmospheric Research Laboratory (ARL) in Boulder, Colorado
by gas chromatography. ARL measured samples from
the NOAA GML network from 2004 through 2016, analyzing flasks from a dozen sites
at first and then rapidly extending the coverage to more than 40 sites.
ARL also made in-situ measurements at Pico (Azores)
and at Summit (Greenland) alongside the flask samples.
In-situ data from the Deutscher Wetterdienst in Hohenpeissenberg (HPB)
were also regularly compared to flask samples collected at this site.
The INSTAAR NMHC laboratory was audited by the World Calibration Center (WCC)
for Volatile Organic Compounds in 2008. All measurement results passed
the quality criteria set by the WCC.
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7. DATA - GENERAL COMMENTS
Method:
The GC analysis involves drying of approximately 600 cc (STP)
of sample gas, then preconcentration of analytes on an adsorbent bed,
followed by thermal desorption onto a short capillary guard column
and main capillary column (HP-Plot AL2O3/KCl 0.53 mm x 60 m) for separation,
and finally detection by a Flame Ionization Detector (FID).
The gas chromatograph used is a HP-5890 series II.
Drying is accomplished by running the sample gas through a tube cooled
to -25°C. The custom-built preconcentration system is cooled to -35°C
and uses Carboxen 1000 and Carboxen 1016 as adsorbents.
Desorption is controlled at 310°C. The flask analysis system is
completely automated, allowing analysis of up to 12 flasks in one sequence.
Calibration:
Analysis of air samples are compared to analysis of synthetic
and compressed air standards. One compressed air standard is run
twice a day to check on the stability of the FID response, the other
standards are ran at least twice a month to determine the response of
the FID. Blanks are prepared by running compressed air through a heated
bed of PtO. Blank samples are analyzed twice daily.
Results:
Results are expressed as mole fractions (pmol/mol)
Uncertainty:
Reproducibility varies by compound and with mole fraction.
It is monitored routinely using the results of the paired flask sampling.
Reproducibility is typically better than 5% RSD.
Lower RSDs are obtained for the higher abundance compounds (ethane, propane).
Accuracy is determined by the calibration standard scale.
A minimum of three independently prepared and cross-referenced standards
is in use at any given time. Deviations in the response factors
from these different standards are smaller than 5%, with results
for ethane and propane typically being equal or less than 2-3%.
Data correction:
After comparing the Isoprene (C5H8) flask data at the German Weather
Service Hohenpeissenberg (HPB) site with results from parallel sampling
and in-situ GC analysis at the site, a systematic correction was applied
to the whole isoprene dataset from 2007 to 2016, to scale the flask data
to the in-situ results. For mole fractions ranging from 8 ppt
(detection limit) to 450 ppt, a polynomial function was applied and
for mole fractions above 450 ppt, a linear function was applied. These
correction functions adjust the original flask results for isoprene by
no more than the larger of 5 pmol/mol or 10%.
The Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia) data have been 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 frequencies 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 for all species may not be available for all sites listed
in the table.
2. The exact location of a sampling site 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 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
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7.3 DATA - EVENT WITH SINGLE PARAMETER
The event data files in ftp://aftp.cmdl.noaa.gov/data/trace_gases/voc/<parameter>/flask/surface/
scheme (see Section 7.2):
[parameter]_[site]_[project]_[lab ID number]_[measurement group]_[optional qualifiers].txt
(ex) C2H6_brw_surface-flask_1_arl.txt contains C2H6 arl 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 ESRL 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).
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)
LEF 2005 12 08 17 34 00 847-99 N C3H6 ARL 53.423 -999.990 ... v1 2006 03 14 00 13
00 45.9100 -90.2600 868.00 472.00 396.00 210595
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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_brw_surface-flask_1_arl.txt contains arl 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 ESRL 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).
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 05 17 17 14 00 1382-99 N 45.9100 -90.2600 868.00 472.00 396.00 217438
C2H2 ARL -75.541 ... C2H4 ARL 76.617 ...
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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.
FLAGS DESCRIPTION:
'...' is a good sample
1st column flags:
'P..' flag: poor flask pair agreement
Since samples are collected in pairs, the pair difference is calculated.
If the mole fraction x falls between the below margins,
and the difference exceeds abs(dx) the flag is applied.
x <= 10 and dx > |5|
11 > x <= 25 and dx > |10|
26 > x <= 63 and dx > |20|
64 > x <= 156 and dx > |40|
157 > x <= 391 and dx > |80|
392 > x <= 977 and dx > |160|
978 > x <= 2441 and dx > |320|
2442 > x <= 6104 and dx > |640|
6105 > x <= 15259 and dx > |1280|
'A..' flag: no data obtained
This flag is applied when there was an instrument failure or if the amount of air left
in the flask was too low for an analysis
'*..' flag:
This flag is applied when an unstable baseline made the peak integration impossible
'D..' flag:
This flag is applied when this particular compound was below the detection limit
of our measurement
'C..' flag:
This flag is applied when a contamination was found
3rd column flags:
'..C' flag:
This flag is applied when the amount of air left in the flask was too low for the
instrument to draw the standard volume for analysis. In that case an analysis
was performed with a reduced sampling volume.
Note:
We feel that this data set best represents hydrocarbons distribution in the remote,
well-mixed global troposphere. It is possible, and even likely, that some values
represent poorly mixed air parcels influenced by local anthropogenic sources.
Users of these data should be aware that further data screening is necessary.
We will provide advice in selecting the data that will best fit the goals
of user's particular investigation.
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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
Helmig, D., Bottenheim J., Galbally I. E., Lewis A., Milton M. J. T.,
Penkett S., Plass-Duelmer C., Reimann S., Tans P., Theil S. (2009)
Volatile Organic Compounds in the Global Atmosphere. Eos Trans. AGU, 90(52),
Feature.
Pollmann J., Helmig D., Hueber J., Plass-Duelmer C., and Tans P. (2008)
Sampling, storage, and analysis of C2-C7 non-methane hydrocarbons
from the US National Oceanic and Atmospheric Administration Cooperative
Air Sampling Network glass flasks. J. Chromatogr., 1188, 75-87.
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