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Atmospheric Hydrogen Mixing Ratios from the
NOAA GMD Carbon Cycle Cooperative Global Air
Sampling Network, 1988-2005
Version: 2006-11-27.1229
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CONTENTS
1. Data source and contacts
2. Use of data
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
7.4 DATA - QC Flags
7.5 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 Laboratory (ESRL)
Global Monitoring Division (GMD)
Carbon Cycle Greenhouse Gases (CCGG)
Correspondence concerning these data should be directed to:
Paul C. Novelli
NOAA ESRL Global Monitoring Division
325 Broadway, GMD-1
Boulder, CO 80305
U.S.A.
Telephone: 303 497-6974
Electronic Mail: Paul.C.Novelli@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
assure that GMD receives fair credit for their work. If the data
are obtained for potential use in a publication or presentation,
GMD should be informed at the outset of the nature of this work.
If the GMD data are essential to the work, or if an important
result or conclusion depends on the GMD data, co-authorship may
be appropriate. This should be discussed at an early stage in
the work. Manuscripts using the GMD data should be sent to GMD
for review before they are submitted for publication so we can
insure that the quality and limitations of the data are accurately
represented.
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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 GMD 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
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6. INTRODUCTION
Individual site files provide H2 mixing ratios in parts
per billion (ppb) (ppb = 1 part in 10^-9 by mole
fraction = nmole/mole) based on measurements from the NOAA
CMDL Carbon Cycle Cooperative Global Air Sampling Network.
In this directory, data are provided through June 30, 1998
for stations from which the first sample was collected before
January 1995. Table 1, accessed below, lists the flask network
sampling location, the 3 letter codes used to identify these
sites, their latitude, longitude and altitude.
Data from sites not provided in this directory may be available
from P. Novelli (CMDL). All air samples were analyzed for H2
at the NOAA CMDL laboratory in Boulder using gas chromatography
with mercuric oxide reduction detection, with all measurements
referenced to an internal H2 calibration scale (Novelli et al.,
1999). During 1988-1991, one flask of a sample pair was analyzed
for H2, and when there was suitable pressure remaining in the
flask, two or more aliquots were measured. We have used the
difference in H2 mixing ratios between the aliquots as an indication
of the precision of the measurements. We used a single point
calibration as the response characteristics of the instrument
had been shown to be linear over a range of 480 to 600 ppb CO
(Novelli et al., 1999).
In October 1991 we began analyzing a single aliquot from
both members of a flask pair (rather than 2 or more aliqouts
from a single flask). The principle reasons for the change were
to simplify flask handling procedures (The CMDL carbon monoxide
and methane projects also measure both flasks of a sample pair)
and to use pair agreement (the difference in mixing ratio between
the two flasks collected simultaneously) as an additional diagnostic
to use in evaluating the quality of the data. We believe that pair
agreement provides quality constraints on the results from collection
through analysis. Novelli et al. (1999) provide a detailed description
of the history of H2 measurements at CMDL.
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7. DATA - GENERAL COMMENTS
Measurements are reported in units of 10^-9 mol H2 per mol
of dry air (nmol/mol) or parts per billion (ppb)) relative
to the NOAA CMDL H2 scale (Novelli et al., 1999). Long-term
measurement uncertainty is estimated to be 15 ppb (~3%). The
absolute accuracy of our H2 scale is unknown. In 2004 a
correction was applied to all measurements made between Dec 1998
and Nov 2002 to account for drift in a working standard. The
drift rate was determined from multiple calibrations using
other H2 standards that are believed stable.
The Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia), Atlantic Ocean Cruise (AOC, US east
coast to South Africa), and Western Pacific Cruise (WPC, New Zealand
and Japan) 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.
The air samples are collected by two general methods: flushing and
then pressurizing glass flasks with a pump, or opening a stopcock on
an evacuated glass flask. During each sampling event, a pair of
flasks is filled.
7.1 DATA - SAMPLING LOCATIONS
Table of NOAA GMD cooperative air sampling sites.
The table includes the three letter code used to identify each
site; the site name; latitude, longitude, and altitude (meters
above sea level) of the sampling location; the number of samples;
the first and last sample dates; and sampling status.
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
http://www.cmdl.noaa.gov/ccgg/iadv/.
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7.2 DATA - FILE NAME DESCRIPTION
Encoded into each file name is the sampling location, platform, and
strategy; measurement laboratory; file content; and gas identifier.
All file names use the following naming scheme:
1 2 3 4 5 6 7
[site][data grouping]_[lab#][strategy][platform]_[qualifier].[gas]
1. [Sampling site]
(ex) brw_, poc_, car_, amt_
2. [Grouping of data within the file]
Data may be grouped by date, latitude, longitude, altitude, etc.
If data are grouped by date then identifier has yyyy[mm][dd] format.
(ex) brw2005_, amt200403_, lef20050315_
If the sampling platform is an aircraft then the identifier is a
3-character numeric field with units of 10^2 meters (hm) above sea level.
(ex) car040_, haa005_
If the sampling platform is a ship then the identifier is a 3-character
alphanumeric field with units of degrees (00-90). Bins in the northern
and southern hemispheres are denoted as n## and s## respectively. The
equatorial bin is denoted as 000.
(ex) pocs25_, poc000_, scsn03_
3. [Measurement laboratory]
A two character numeric field identifies the measurement laboratory (01-99).
NOAA GMD is lab number 01 (see http://www.cmdl.noaa.gov/ccgg/globalview/labs/).
4. [Sampling strategy]
A single alphanumeric character (0-9,a-z,A-Z) indicates the sampling strategy.
_??C Semi-continuous
_??D Discrete
5. [Sampling platform]
A single alphanumeric character (0-9,a-z,A-Z) indicates the sampling platform.
_???0 Land
_???1 Ship
_???2 Aircraft
_???3 Tower
6. [Qualifier]
An alphanumeric string describes the type of data included in the file.
_????_event Data from every collection event
_????_mm Computed monthly mean values
_????_hr Computed hourly averages (semi-continuous data only)
_????_day Computed daily averages (semi-continuous data only)
_????_all All Data
7. [Gas]
Identifies the trace gas species.
_????_???.co2 Carbon dioxide
_????_???.ch4 Methane
_????_???.co2c13 d13C (co2)
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7.3 DATA - EVENT
The data files "ccg/h2/flask/event/" use the following naming
scheme (see Section 7.2):
xxx[data grouping]_01D[platform]_event.h2
(ex) pocn30_01D1_event.h2 contains all event data from
POC samples collected from a moving ship and grouped at
30N +/- 2.5 degrees.
(ex) brw_01D0_event.h2 contains all event data from
from BRW samples collected from a fixed position.
The data files contain multiple lines of header information
followed by one line for each atmospheric measurement.
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: [FLASK ID] The sample container ID.
Field 8: [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 CMDL 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 9: [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).
Field 10: [MEASURED VALUE] Dry air mole fraction or isotopic composition.
Missing values are denoted by -999.99[9].
Field 11: [QC FLAG] A three-character field indicating the results of our
data rejection and selection process, described in section 7.4.
Field 12: [INSTRUMENT] A 2-character code that identifies the instrument
used for the measurement.
Field 13: [YEAR] The measurement date and time in LT.
Field 14: [MONTH]
Field 15: [DAY]
Field 16: [HOUR]
Field 17: [MINUTE]
Field 18: [LATITUDE] The latitude where the sample was collected, (negative (-)
numbers indicate samples collected in the southern hemipshere).
Field 19: [LONGITUDE] The longitude where the sample was collected, (negative (-)
numbers indicate samples collected in the western hemisphere).
Field 20: [ALTITUDE] The altitude where the sample was collected (masl).
Field 21: [WIND SPEED] Wind Speed (m/s) as reported by the field operator
during sample collection. Please note: CCCG has no means by which
to assess the reliability of these recorded observations.
Field 22: [WIND DIRECTION] Wind Direction (degrees) as reported by the field
operator during sample collection. Please note: CCGG has no means
by which to assess the reliability of these recorded observations.
Field 23: [EVENT NUMBER] A long integer that uniquely identifies the sampling
event.
Fields in each line are delimited by whitespace.
(ex)
KEY 2004 12 17 15 00 2185-99 D co2 400.170 -.. L3 2005 01 03 13 52 25.66 -80.20 3.00 4.6 90 193357
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7.4 QC FLAGS
NOAA GMD 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 COMMENT 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 determined.
If both the first and second column contain a period (e.g., "..." and "..I"),
the sample is RETAINED.
Since samples are collected in pairs, the pair
difference is calculated, and samples with a
pair difference greater than 15 ppb are flagged.
Retained and rejected flasks are flagged as follows.
(NOTE: If either the first or second of these characters
is not a period, the sample has been rejected.)
Flag Description
Retained ... good pair
(D <= 15 ppb)
Rejected .X. Not representative of background
conditions (> 3 sigma from a fitted
curve), may include unidentified
sampling/analysis problems.
.N. High/low mixing ratio thought
to not represent background
condiitons.
P.. Poor flask pair agreement
(D > 15 ppb)
Z.. Poor aliquot agreement
(D > 7.5 ppb)
*.. off scale result, broken flask or
unacceptable analysis
W.. Wrong flask type for H2
S.. Sample was collected through the CO2
intake for the in situ analyzer
..I Flask is one of the pair used in an
intercomparison with the cooperating
agency
The retained values comprise the data set that we feel best
represents the H2 distribution in the remote, well-mixed
global troposphere. It is possible, and even likely, that
some values flagged as non-background conditions are valid
measurements, but represent poorly mixed air parcels
influenced by local anthropogenic sources or strong local
biospheric sources or sinks. Users of these data should be
aware that data selection is a difficult but necessary aspect
of the analysis and interpretation of atmospheric trace gas
data sets, and the specific data selection scheme used may be
determined by the goals of a of a particular investigation.
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7.5 DATA - MONTHLY AVERAGES
The data files "ccg/h2/flask/month/" use the following naming
scheme (see Section 7.2):
xxx[data grouping]_01D[platform]_mm.h2
(ex) pocn30_01D1_mm.h2 contains computed monthly mean values
from POC samples collected from a moving ship and grouped at
30N +/- 2.5 degrees.
(ex) brw_01D0_mm.h2 contains computed monthly mean values
from BRW samples collected from a fixed position.
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
In these files a monthly mean value of -999.99 denotes months where there
are insufficient data to calculate a monthly mean.
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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.Z ! transfer the file
3. ftp> bye ! leave ftp
4. $ uncompress filename.tar.Z ! uncompress 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
Lang, P.M., L.P. Steele, R.C. Martin, and K.A. Masarie, Atmospheric
methane data for the period 1983-1985 from the NOAA/GMCC global
cooperative flask sampling network, NOAA Technical Memorandum ERL
CMDL-1, 1990a.
Lang, P.M., L.P. Steele, and R.C. Martin, Atmospheric methane data for
the period 1986-1988 from the NOAA/CMDL global cooperative flask
sampling network, NOAA Technical Memorandum ERL CMDL-2, 1990b.
Novelli, P.C., K.A. Masarie, and P.M. Lang, Molecular hydrogen in the
troposhere: Global distributions and budget, J. Geophys Res., 104,
30,427-30,444, 1999.
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.
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