--------------------------------------------------------------------- Atmospheric Carbon Dioxide Dry Air Mole Fractions from Quasi-continuous Measurements from the NOAA GML Carbon Cycle Aircraft Program, 2020-2022. Version: 2023-01-06 -------------------------------------------------------------------- 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) Global Monitoring Laboratory (GML) Carbon Cycle Greenhouse Gases (CCGG) Correspondence concerning these data should be directed to: Kathryn McKain NOAA Global Monitoring Laboratory 325 Broadway, GML-1 Boulder, CO 80305 U.S.A. email: kathryn.mckain@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 see individual data files for citation text. -------------------------------------------------------------------- 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 +++++++++++++++++++++++++++++++ Project-specific notes: -------------------------------------------------------------------- 6. INTRODUCTION These files contain quasi-continuous atmospheric measurements of dry air mole fractions of carbon dioxide collected from aircraft by the NOAA GML Carbon Cycle Aircraft Program during short-term campaigns and at ongoing sites. Flight tracks often include continuous ascending and descending vertical profiling from the near-surface to higher altitudes. Vertical profile data are useful for a variety of analyses in atmsopheric science, including assessment of remote-sensing total-column retrievals, evalution of vertical mixing and atmospheric transport, measurement of a set of values that reflect shorter and longer space/time scales, and for quantification of surface fluxes. When available, datasets will include a parameter which identifies individual vertical profiles. Contact NOAA GML for more specific information about individual datasets. ------------------------------------------------------------------- 7. DATA - GENERAL COMMENTS 7.1 DATA - SAMPLING LOCATIONS For a summary of sampling locations, please visit https://www.esrl.noaa.gov/gmd/ccgg/insitu/. or https://gml.noaa.gov/ccgg/aircraft/. 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 TYPE 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 DATA - 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 DATA - COLLECTION METHODS Although the measurement setup has varied slightly for each campaign and project due different requirements and constraints, there are common methodological approaches which are typically utilized by the NOAA GML Aircraft Program for insitu measurements (Karion et al. 2013). Aircraft insitu measurements are made with the Picarro G2401-m cavity ring-down spectrometer (Crosson 2008). Sample air is delivered to the analyzer from an inlet that is mounted on the exterior of the aircraft via 1/8" stainless steel tubing and a pump located downstream of the analyzer. Mass flow for each analyzer and setup is typically ~150-200 sccm. Volume flow varies with temperature and pressure. Reported measurement times are corrected for lag time in the sample line. The native time resolution of individual analyzers is typically between 2 and 4 seconds and may vary slightly over time and among analyzers. Sample air is typically not dried. Dry air mole fractions are computed using analyzer-specific empirical corrections, derived from laboratory tests performed before and after deployment to the field, that account for dilution and pressure-broadening effects (Rella et al. 2013, Chen et al. 2013). Repeated characterization of the water correction for individual analyzers allows for uncertainty estimation of this term. Analyzers are typically calibrated in the lab before and after each field deployment against 6-7 tanks that cover a wide range of values. Calibration tank values are assigned by the Central Calibration Laboratory at NOAA GML (https://gml.noaa.gov/ccl/) and are traceable to World Meteorological Organization (WMO) scales. One or two calibration cylinders is often flown with the analyzer and measured before, during, and after each flight. When available, in-flight calibration measurements are typically used to derive a single offset correction for individual flights (Karion et al. 2013). Reported uncertainties include consideration of uncertainty in the water correction, lab and in-flight calibration, precision, and uncertainty in values assinged to calibration tanks. If in-flight calibrations are not available, repeated lab calibrations are used estimate the uncertainty due to variability and drift in analyzer response. Continuous measurement of tank air during flight has also been used to investigate the sensitivity of the measurement to changing conditions typically of flight conditions. When available, comparison with independent measurements is also considered in the uncertainty analysis. ------------------------------------------------------------------- 8. DATA RETRIEVAL All (ASCII text and netCDF) files are located in "https://gml.noaa.gov/aftp/data/trace_gases/co2/pfp/aircraft/". 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 Chen H., A. Karion, C. W. Rella, J. Winderlich, C. Gerbig, A. Filges, T. Newberger, C. Sweeney, P. P. Tans (2013) Accurate measurement of carbon monoxide in humid air using the cavity ring-down spectroscopy (CRDS) technique, Atmsopheric Measurement Techniques, 6, 4, doi: 10.5194/amt-6-1031-2013. Crosson E. R. (2008) A cavity ring-down analyzer for measuring atmospheric levels of methane, carbon dioxide, and water vapor, Applied Physics B, 92, doi: 10.1007/s00340-008-3135-y. Karion A., C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. E. Andrews, J. Kofler, D. Neff, P. Tans (2013) Long-term greenhouse gas measurements from aircraft, Atmospheric Measurement Techniques, 6, 3, doi: 10.5194/amt-6-511-2013. Rella, C. W., H. Chen, A. E. Andrews, A. Filges, C. Gerbig, J. Hatakka, A. Karion, N. L. Miles, S. J. Richardson, M. Steinbacher, C. Sweeney, B. Wastine, C. Zellweger (2013) High accuracy measurements of dry mole fractions of carbon dioxide and methane in humid air, Atmospheric Measurement Techniques, 6, 3, doi: 10.5194/amt-6-837-2013. -------------------------------------------------------------------