---------------------------------------------------------------------

Atmospheric Dry Air Mole Fractions of chcl3 from the NOAA GML Surface
and Aircraft Vertical Profile Network.

Version: 2023-05-16
--------------------------------------------------------------------
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

--------------------------------------------------------------------
1. DATA SOURCE AND CONTACTS

National Oceanic and Atmospheric Administration (NOAA)
Earth System Research Laboratories (ESRL)
Global Monitoring Laboratory (GML)
Halocarbons & other Atmospheric Trace Species Group (HATS)

Correspondence concerning these data should be directed to:

Isaac Vimont and Stephen Montzka
NOAA ESRL Global Monitoring Laboratory
325 Broadway, MS: R/GML1
Boulder, CO 80305
U.S.A.

email: isaac.vimont@noaa.gov
steve.montzka@noaa.gov

--------------------------------------------------------------------
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

Vimont, I., Montzka, S., Crotwell, M., Andrews, A., Baier, B., Hall, B.,
Handley, P., Higgs, J., Kofler, J., Legard, T., McKain, K., Miller, J., Moglia,
E., Mund, J., Neff, D., Newberger, T., Petron, G., Sweeney, C., Turnbull, J., Wolter, S.,
& NOAA Global Monitoring Laboratory. (2022). Atmospheric Dry Air Mole Fractions of
chcl3 from the NOAA GML Surface and Aircraft Vertical Profile Network.
[Data set]. NOAA GML. Version 2023-05-16. https://doi.org/10.15138/adas-g698

--------------------------------------------------------------------
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.

--------------------------------------------------------------------
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.

--------------------------------------------------------------------
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:

--------------------------------------------------------------------
6. INTRODUCTION

All samples were analyzed for GCMS analytes (mostly halocarbons) at
NOAA ESRL in Boulder, Colorado by gas chromatography / mass spectrometric
detection, and each sample aliquot was referenced to the analyte specific standard
scale (see Hall et al. 2007).

Estimates of the uncertainty associated with each GCMS measurement are
not yet available. It is expected that this will be included in future
updates.

-------------------------------------------------------------------
7. DATA - GENERAL COMMENTS

GCMS analyses involve extraction of approximately 150-400 cc(STP) of the
whole air sample through two cryogenic preconcentration traps, subsequent
thermal desorption onto a capillary precolumn and then a capillary main
column before final detection of the mass/charge ration specific to each
analyte (Montzka et al., 1993). Sample volumes vary based on the number of
additional measurements to be performed on each sample subsequent to the GCMS
extraction. To account for the variable sample volumes, the GCMS analysis
system is routinely checked for non-linearities and non-linearity corrections
are made where necessary. Analyses of PFP air samples are compared to
analyses of known (calibrated) compressed air standards. Analytical results
are expressed as dry gas mole fractions (pmol/mol or ppt) on the specified
compound specific scale. Reproducibility varies by compound but are
typically less than 5% RSD, with better reproducibility for the higher
abundance compounds.

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.

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.

-------------------------------------------------------------------
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/.

-------------------------------------------------------------------
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

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

-------------------------------------------------------------------
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.

-------------------------------------------------------------------
7.4 DATA - CONTENT

See individual files for description of the provided variables and other
dataset metadata.

-------------------------------------------------------------------
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.

NOTE: For this data set, preliminary selection
flags have been added to denote if a data point
is above or below the general “background” for a
given site. At this time, these selection flags
are still being developed, and as such, a given
datapoint’s flag status is subject to change in
future releases, once the statistical methods are
perfected and deemed appropriate for this use.
Data points with this flag should be considered
valid at this time, and the end user is encouraged
to evaluate which data (with the selection flag) are
appropriate for their individual use.

-------------------------------------------------------------------
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.
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.
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. 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.)
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).

-------------------------------------------------------------------
8. DATA RETRIEVAL

All (ASCII text and netCDF) files are located in
"https://gml.noaa.gov/aftp/data/trace_gases/gcms/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.

-------------------------------------------------------------------
9. REFERENCES

Hall, B. D., G. S. Dutton, and J. W. Elkins (2007), The
NOAA nitrous oxide standard scale for atmospheric observations,
J. Geophys. Res., 112, D09305, doi:10.1029/2006JD007954.

Montzka, S. A., R. C. Myers, J. H. Butler, J.W. Elkins, and
S.O. Cummings (1993), Global tropospheric distribution and
calibration scale of HCFC-22, Geophys. Res. Lett., 20, 703-706.

-------------------------------------------------------------------