Bay Area Air Quality Management District Greenhouse Gas (GHG) Diurnal Data ReadMe File --------------------------------------------------------------------- Diurnal profiles of atmospheric dry air mole fractions from continuous measurements at fixed-site GHG monitoring stations in the San Francisco Bay Area, California, 2017 Bay Area Air Quality Management District (BAAQMD) Planning and Climate Protection Division (PCP) Climate Protection Section (CP) Greenhouse Gas Measurement Program (GHG-MP) Version: 2017-07-18 -------------------------------------------------------------------- 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 8. Data retrieval -------------------------------------------------------------------- 1. DATA SOURCE AND CONTACTS These directories contain diurnal profiles of atmospheric CH4, CO2 and CO dry-air mole fractions from up to four fixed-site GHG stations: Bodega Bay (BBY), Bethel Island (BIS), Livermore (LIV), Patterson Pass (PTP) and San Martin (SMT). Correspondence concerning these data should be directed to: Primary Contact Dr. Abhinav Guha BAAQMD Planning and Climate Protection Division 375 Beale Street, Suite 600 San Francisco, CA 94105 Telephone: 415-749-5192 Electronic Mail: aguha@baaqmd.gov Secondary Contact Dr. Sally Newman BAAQMD Planning and Climate Protection Division 375 Beale Street, Suite 600 San Francisco, CA 94105 Telephone: 415-749-8715 Electronic Mail: snewman@baaqmd.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. BAAQMD relies on the ethics and integrity of the user to insure that the agency receives fair credit for their work. If the data are obtained for potential use in a publication or presentation, BAAQMD should be informed at the outset of the nature of this work. If the BAAQMD data are essential to the work, or if an important result or conclusion depends on the BAAQMD data, co-authorship may be appropriate. This should be discussed at an early stage in the work. Manuscripts using BAAQMD data should be sent 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 Guha, A., S. Newman, J. Bower, P. Martien, I. Perkins (2017), Diurnal profiles of atmospheric dry air mole fractions from continuous measurements at fixed-site GHG monitoring stations in the San Francisco Bay Area, California, 2017, Version: 2017-07-18, Path: www.baaqmd.gov/ghgdata -------------------------------------------------------------------- 3. RECIPROCITY Use of these data implies an agreement to reciprocate. Research groups utilizing these measurements agree to make their own data available to BAAQMD in an equally complete and easily accessible form. -------------------------------------------------------------------- 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 +++++++++++++++++++++++++++++++ Site-specific notes: 2017-07-18 The CH4, CO2 and CO in-situ measurements at SMT are missing from March 15 to 17, then from March 26 to 30, and finally from April 27 to May 11 due to site repair and maintenance. +++++++++++++++++++++++++++++++ Project-specific notes: GHG measurements have been discontinued at PTP and the instrument has been relocated to LIV which will serve as a permanent site from December 1, 2016 -------------------------------------------------------------------- 6. INTRODUCTION At all sites, CH4, CO2 and CO measurements are made using a laser-based near-infrared analyzer (Model G2401, Picarro Incorporated, Mountain View, California, USA) based on the principles of Cavity Ring-Down Spectroscopy. The G2401 also measures water vapor (H2O). The water vapor data is processed by the instruments' computer to internally derive and apply the water vapor correction to the trace parameter data values to generate dry air mole fractions. (Rella et al., 2010; Chen et al., 2013; Welp et al., 2013). The original data (~ 1 Hz) are retrieved by a data logger every 10 sec and then processed into 1-minute averages before the logger pushes the data to the Air District's internal Data Management Server (DMS). The 1-minute averages are then used to calculate 5-minute averages and hourly averages by the DMS and stored there. A well-calibrated secondary "target" cylinder is sampled once in 72 hours (three days) for 5 minutes. Target checks are regularly plotted in a time series to keep an account of the drift of the instrument and precision of the measurements. The instruments were calibrated initially, to derive "slope" and "offset" calibration coefficients to correct each intrument's "measured" concentrations to "true" concentrations, using high-accuracy primary gas tanks prepared at National Oceanic and Atmospheric Administration (NOAA's) Earth Sciences Research Laboratory Global Monitoring Division (ESRL-GMD) in Boulder, Colorado and provided to the Air District by the Monitoring Division of California Air Resources Board (CARB). Thereafter "high" and "low" secondary gas standards (previously calibrated against the primary NOAA standards) are passed through the instruments periodically and analyzed to correct for changes in instrument operation. Approximately annually, the secondary "high" and "low" gas standards are recertified using the primary NOAA standards. The original slope and offset corrections, drift corrections from the frequent "target" cylinder runs, and changes in slope and offset from the periodic secondary standard analyses are applied to the raw data during post-processing in order to obtain a corrected dataset. Data are edited using a Matlab-based algorithm to exclude measurements obtained when the instrument was either not working optimally, or was not sampling ambient air or when the operator was performing a procedure that involved the instrument or its sampling manifold. The accompanying "quality control code" and "operational code" for each data value is used to replace invalid data with NaNs in the final data set. Invalid data points include but not limited to measurements during and following a "target" check or during calibrations, frozen / sticky valves due to instrument malfunction or power loss, negative / missing data value, operator-flagged data during occasional maintenance and so on. As long as less than 25 % of the minute averages in a given hour are missing, the hourly average is considered to be valid data. ------------------------------------------------------------------- 7. DATA - GENERAL COMMENTS 7.1 DATA - SAMPLING LOCATIONS There are a total of five sites where temporary or permanent fixed-site GHG monitoring stations are deployed. Their locations are - Bodega Bay 38.318756 N, 123.072528 W, elevation: 21 m a.s.l Bethel Island 38.006311 N, 121.641918 W, elevation: -2 m a.s.l Livermore 37.687526 N, 121.784217 W, elevation: 137 m a.s.l San Martin 37.079379 N, 121.600031 W, elevation: 86 m a.s.l Patterson Pass 37.689615 N, 121.631916 W, elevation: 526 m a.s.l where - m a.s.l - meters above sea level ------------------------------------------------------------------- 7.2 DATA - FILE NAME DESCRIPTION Encoded into each file name are the parameter name (trace gas identifier), reporting units, reporting interval, site, season of year, year at start of season and post-processing iteration that further define the file contents. All file names use the following naming scheme: 1 2 3 4 5 6 7 [parameter]_[unit]_[data type]_[site]_[season]_[year]_[iteration] 8 .[file type] 1. [parameter] Identifies the measured parameter or trace gas species. CO2 Carbon Dioxide CH4 Methane CO Carbon Monoxide 2. [unit] Identifies the reporting units of the parameter. ppm parts per million ppb parts per billion 3. [time interval] Identifies the data profile type diurnal 4. [site] Identifies the sampling site. BodegaBay Bodega Bay (BBY) BethelIsland Bethel Island (BIS) Livermore Livermore (LIV) Patterson Patterson Pass (PTP) SanMartin San Martin (SMT) 5. [season] Identifies the season for which data is reported. Summer Jun 1 - Aug 31 Fall Sep 1 - Nov 30 Winter Dec 1 - Feb 28/29 Spring Mar 1 - May 31 6. [year] Identifies the year at the start of the reporting period. 7. [iteration] Identifies the post-processing status of the reported data. raw preliminary final 8. [file type] Identifies the format in which the file is saved by default csv xlsx txt ------------------------------------------------------------------- 7.3 DATA - FILE TYPE Data is provided in the comma separated value file format (.csv). ------------------------------------------------------------------- 7.4 DATA - CONTENT For each site, we provide a 24-hour diurnal profile with mean concentrations at each hour being derived from hourly-averaged data for the entire season. In each data file, there are five columns of data. The first column represents the "hour of day" of the corresponding data value in the second column. The second column represents the "mean ambient concentration" of the measured parameter at the "hour" noted in the first column. Note that CO2 is reported in ppm units while CH4 and CO are reported in ppb units. The third column represents "one standard deviation" of the "mean" in the second column. The fourth column represents "mean plus standard deviation". The fifth column represents "mean minus standard deviation". In a particular row, the "hour of day" corresponds to the start of the sampling period of the concentration data reported in the second column. ------------------------------------------------------------------- 8. DATA RETRIEVAL Users may directly click on the 'data downloads' link and save the file in their device as a .csv file. The file will be saved with a pre-set file name as described in Section 7.2. The README file is a text file and can be saved in the .txt format. ------------------------------------------------------------------- 9. REFERENCES Chen, H., Karion, A., Rella, C. W., Winderlich, J., Gerbig, C., Filges, A., Newberger, T., Sweeney, C., and Tans, P. P.: Accurate measurements of carbon monoxide in humid air using the cavity ring-down spectroscopy (CRDS) technique, Atmos. Meas. Tech., 6, 1031-1040, doi:10.5194/amt-6-1031-2013, 2013. Rella, C.: Accurate Greenhouse Gas Measurements in Humid Gas Streams Using the Picarro G1301 Carbon Dioxide / Methane / Water Vapor Gas Analyzer, White Paper, 2010, https://www.picarro.com/ products_solutions/trace_gas_analyzers/co_co2_ch4_h2o Welp, L. R., Keeling, R. F., Weiss, R. F., Paplawsky, W., and Heckman, S.: Design and performance of a Nafion dryer for continuous operation at CO2 and CH4 air monitoring sites, Atmos. Meas. Tech., 6, 1217-1226, doi:10.5194/amt-6-1217-2013, 2013. ------------------------------------------------------------------- Bay Area Air Quality Management District www.BAAQMD.gov 415.749.5000 | 1.800.HELP AIR 375 Beale St. Suite 600, San Francisco CA 94105