These data were produced by NOAA and are not subject to copyright protection in the United States. NOAA waives any potential copyright and related rights in these data worldwide through the Creative Commons Zero 1.0 Universal Public Domain Dedication (CC0 1.0)
CC0 1.0 Universal
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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 or 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)
+++++++++++++++++++++++++++++++
Project-specific notes:
2022-11-01
Datasets are provided in the self describing ObsPack format.
See https://gml.noaa.gov/ccgg/obspack/ for details.
Surface pfp event data are available in NetCDF and ASCII text.
+++++++++++++++++++++++++++++++
Parameter-specific notes:
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6. INTRODUCTION
For the past three decades CO has been measured in discrete samples of air
collected as part of the NOAA Collaborative Global Air Sampling Network. Three
analytical methods were used. From 1988 to 2008 instruments based on gas
chromatography and HgO reduction detection were used (GC-HgO, instruments from
Trace Analytical Inc.) The instruments had a nonlinear response over the range
of the remote troposphere (Novelli et al., 1991). Response curves composed of
4-8 standards defined instrument response (Novelli et al., 1994, 1998).
In 2008 an analyzer based on CO fluorescence in the vacumm ultra violet (VUV,
Gerbig et al.,1996) replaced one of the two GCs on the measurement system. The
remaining GC and the VUV instrument were calibrated using a common set of
reference gases, ranging from 50 to 350 ppb. In 2010 the last GC was replaced by
a VUV instrument.
Since August 2019, all samples are analyzed for CO by Tunable Infrared Laser
Direct Absorption Spectroscopy. The TILDAS instrument is calibrated regularly
using 11 standards, ranging from 23 to 486 ppb. In this range, the instrument
response is linear.
A review of the four sets of primary standards prepared between 1989-2000
suggested our working standards were drifting upward at rates of ~0.5-1 ppb
year. A time dependant correction was applied to all air samples measured
through 12/2000 (Novelli et al., 2003). It is now believed primary standards
prepared in 1999/2000 were biased. They were assigned new mole fractions based
on their calibrations versus primary standards prepared in 2006, 2011 and 2015
and the flask air measured against these standards were re-calculated.
Instruments used in the analysis are identified in the data string by their ID.
The GC-HgO instruments were R2,CS, R5 and R6. The VUV instruments are V2, V3 and
V4. The TILDAS instrument is AR2.
The flask data will be reprocessed when the CO calibration scale is updated and
uncertainty estimates will be provided.
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7. DATA - GENERAL COMMENTS
Carbon monoxide mixing ratios in these files are reported in units of nmol/mol
(10^-9 mole CO per mole of dry air or as part per billion by mole fraction
(ppb)) relative to the NOAA/WMO CO scale (Novelli et al., 1991, Novelli et al.,
2003). The reproducibility of the measurements, estimated from repeated
analysis of air contained in a high-pressure cylinder, is ~1-2 ppb using GC-HgO,
0.5 ppb or better for the VUV instruments, and 0.1 ppb for the TILDAS.
Air samples are collected in programmable flask packages (PFP) using
programmable compressor packages (PCP). The PCP contains battery-powered pumps
for flushing and pressuring the flasks. The PFP contains twelve 0.7L cylindrical
borosilicate glass flasks with glass valves on each end sealed with Teflon
O-rings, a stainless-steel manifold on each side of the flasks, and a data
logging and control system.
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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/.
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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 TYPES
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 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 COLLECTION METHODS
A single-character code is used to identify the sample collection method.
The codes are:
A - The automated or manual filling of a whole air sample using the
Programmable Flask Package (PFP) and Programmable Compressor Package (PCP)air
sampling devices. The air sample is contained in a 0.7 liter borosilicate
glass container (flask) fitted with two Glass Expansion high vacuum glass
piston valves sealed with PTFE O-rings. The flasks are typically flushed with
10 liters (aircraft samples) or 75 liters (tower samples) of ambient air and
then pressurized to 40 psia. Air is delivered through an intake tube using
two diaphragm pumps connected in series and controlled with a microprocessor.
The flow rate is approximately 15 L/min at sea level. See Sweeney et al.
2015 and Andrews et al. 2014 for more details.
C - Air samples are collected as with method 'A', but the sample air is
dried before sample collection. Flasks are not pre-filled with ambient air
before flushing and collecting the air sample.
I - Air is sampled from a 15L spherical stainless steel mixing volume
after being filled with ambient air that was pulled through an M&C Techgroup
Model ECP 20-2 gas chiller using an integrating compressor and mass flow
controller. The two stainless steel dryer traps are plumbed in series, held
at approximately 5 degrees C and the condensed water is removed with a
peristaltic pump. Prior to sample collection, an additional glass
conditioning step known as "prefilling" occurs where the glass containers are
flushed and filled with ambient air and then vented and flushed immediately
before air sample collection. This is a glass conditioning step that
addresses glass wall effects of the gases of interest. After 'prefilling',
the integration starts with a high flow rate of 3.8 SLM and decreases over
time to 0.29 SLM over 1 hour. The resulting one hour time averaged ambient
air sample is compressed into a 0.75 liter borosilicate glass container
(flask) fitted with 2 Glass Expansion high vacuum glass valves and PTFE
O-rings. The flask is typically filled to 40 psia. (See Turnbull, J.C.,
Guenther, D., Karion, A., Sweeney, C., Anderson, E., Andrews, A.E., Kofler,
J., Miles, N.L., Newberger, T., Richardson, S.J., Tans, P.P., 2012. An
integrated flask sample collection system for greenhouse gas measurements.
Atmos. Meas. Tech. 5, 2321-2327.)
B - Air samples are collected as with method 'R', but with an additional
drying step using one of several techniques. In one method, e.g. site=ACT,
air samples were dried with a two-stage chiller cooled to 5 degrees C; those
taken below 3000 m MSL were also pressurized to 40 psia to further facilitate
air sample drying (Baier et al. 2019). At tower sampling sites, M&C chillers
with temperatures set to approximately 3 degrees C and sub-ambient pressure
due to high flow are used (Andrew et al. 2014). At CRV tower, a two-stage
chiller set to -26 degrees C is used.
R - Air samples are collected as with method 'A', but with an additional
glass conditioning step known as "prefilling". During prefilling, the glass
containers are flushed and filled with ambient air and then vented and
flushed immediately before air sample collection. This is a glass
conditioning step that addresses glass wall effects of the gasses of interest
(Andrews et al. 2014).
X - Testing method for pfp drying experiments. CP-> chiller pressurized
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8. DATA RETRIEVAL
All (ASCII text and netCDF) files are located in
"https://gml.noaa.gov/aftp/data/trace_gases/co/pfp/surface/".
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
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., J.E. Elkins, and L.P. Steele, The development
and evaluation of a gravimetric reference scale for
measurements of atmospheric carbon monoxide, J. Geophys.
Res., 96, 13,109-13,121, 1991.
Novelli, P.C., L.P. Steele, and P.P. Tans, Mixing ratios of
carbon monoxide in the troposphere, J. Geophys. Res., 97,
20,731-20,750, 1992.
Novelli, P.C., J.E. Collins, Jr, R.C. Myers, G.W. Sachse,
and H.E. Scheel, Reevaluation of the NOAA/CMDL carbon
monoxide reference scale and comparisons to CO reference
gases at NASA-Langley and the Fraunhofer Institute, 99,
12,833- 12,839, 1994.
Novelli, P.C., K.A. Masarie, and P.M. Lang, Distributions
and recent changes in carbon monoxide in the lower
troposphere, J. Geophys. Res., 103, 19,1015- 19,033, 1998.
Novelli, P.C., K.A. Masarie, P.M. Lang, B.D. Hall, R.C. Myers,
and J.W. Elkins, Re-analysis of tropospheric CO trends:
Effects of the 1997-1998 wild fires, J. Geophys. Res., 108,
D15 : 4464, doi:10.1029/2002JD003031, 2003.
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