--------------------------------------------------------------------- Atmospheric Carbon Dioxide Dry Air Mole Fractions from NOAA GML Tall Tower and other Continental Sites 2005-Present Version: 2023-08-23 -------------------------------------------------------------------- CONTENTS 1. Data source and contacts 2. Use of data 2.1 Citation 3. License 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) Global Monitoring Laboratory (GML) Carbon Cycle Greenhouse Gases (CCGG) Correspondence concerning these data should be directed to: Xin Lan NOAA Global Monitoring Laboratory 325 Broadway, GML-1 Boulder, CO 80305 U.S.A. email: Xin.Lan@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. To ensure that GML receives fair credit for their work please include relevant citation text in publications. We encourage users to contact the data providers, who can provide detailed information about the measurements and scientific insight. In cases where the data are central to a publication, coauthorship for data providers may be appropriate. 2.1 CITATION Please reference these data as Andrews, A., Crotwell, A., Crotwell, M., Handley, P., Higgs, J., Kofler, J., Lan, X., Legard, T., Madronich, M., McKain, K., Miller, J., Moglia, E., Mund, J., Neff, D., Newberger, T., Petron, G., Turnbull, J., Vimont, I., Wolter, S., & NOAA Global Monitoring Laboratory. (2023). NOAA Global Greenhouse Gas Reference Network Flask-Air PFP Sample Measurements of CO2 at Tall Tower and other Continental Sites, 2005-Present [Data set]. NOAA GML. https://doi.org/10.15138/gr3w-qm07 Version: 2023-08-23. -------------------------------------------------------------------- 3. LICENSEThese 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 -------------------------------------------------------------------- 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 CO2 dry air mole fractions reported in these files were measured by a nondispersive infrared absorption analyzer or cavity ring-down spectrometer (since Aug., 2019) in air samples collected in glass flasks at NOAA GML Carbon Cycle Cooperative Global Air Sampling Network sites. Measurements are reported on the X2019 CO2 mole fraction scale. Calibration procedures are given in Komhyr et al., 1983; Komhyr et al., 1985; Thoning et al., 1987, and Thoning et al., 1995; and Tans et al.,2017. Analysis and interpretation of the data have been reported by Komhyr et al., 1985; Conway et al., 1988; Tans et al., 1989a; Tans et al., 1990, and Conway et al., 1994. ------------------------------------------------------------------- 7. DATA - GENERAL COMMENTS Carbon dioxide (CO2) in ambient and standard air samples is detected using a non-dispersive infrared (NDIR) analyzer. The measurement of CO2 in air is made relative to standards whose CO2 mole fraction is determined with high precision and accuracy. Because detector response is non-linear in the range of atmospheric levels, ambient samples are bracketed during analysis by a set of standards used to calibrate detector response. Measurements are reported in units of micromol/mol (10^-6 mol CO2 per mol of dry air or parts per million (ppm)). In August, 2019, we switched from a NDIR to a Cavity Ring-Down Spectrometer that analyzes CH4 and CO2. The analyzer is calibrated off-line with a suite of standards once per month relative to a dry, natural air, reference in a high-pressure cylinder. All air samples are measured relative the same reference, and CH4 and CO2 values in measured samples are calculated based on their ratio to the reference. Repeatability of the analyzer, based on repeated analysis of air from a high-pressure cylinder, is ~0.02 ppm (1 sigma). Measurements are directly traceable to the WMO X2019 CO2 in air mole fraction scale. 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 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 ------------------------------------------------------------------- 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. ------------------------------------------------------------------- 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 ------------------------------------------------------------------- 8. DATA RETRIEVAL All (ASCII text and netCDF) files are located in "https://gml.noaa.gov/aftp/data/trace_gases/co2/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 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. -------------------------------------------------------------------