In Situ Carbon Dioxide and Methane Mole Fractions from the Los Angeles Megacity Carbon Project

Description

The Los Angeles Megacity Carbon Project was designed to demonstrate a scientifically robust measurement of multi-year emission trends for carbon dioxide and methane in an urban environment (i.e. megacity) and attribute these trends to emissions from various sectors. Determination of greenhouse gas fluxes and uncertainties in urban areas is critical for evaluating mitigation strategies. The current LA surface observation network includes twelve in situ analyzers situated on tower- or rooftop/building- based platforms for continuous measurements of carbon dioxide, methane and carbon monoxide (note: not all species are measured at all sites). The data from the in situ towers are currently being used in both forward and inverse-modeling frameworks and the inverse model results will be used to estimate carbon fluxes for Southern California down to a resolution of 1 km^2. The Hestia project (http://hestia.project.asu.edu/) has produced a bottom-up, sectorally-resolved inventory estimating fossil carbon emissions for five counties in the South Coast Air Basin, including Los Angeles, with unprecedented space/time resolution. The LA Megacity project also includes flask sampling of 14CO2 and other trace gases at three sites. The Caltech site also includes a total carbon column observing network (TCCON, https://tccon-wiki.caltech.edu/) remote sensing station, a mini-micropulse lidar (mini-MPL, Sigma Space, Inc.,http://www.sigmaspace.com/) and ceilometer (Vaisala Instruments, http://www.vaisala.com/en/Pages/default.aspx). In addition, the California Laboratory for Atmospheric Remote Sensing (CLARS, https://tmf.jpl.nasa.gov/clarsweather/) instrument on Mt. Wilson measures the slant column abundance of greenhouse gases by rastering across the LA basin roughly every 90 minutes. There have also been periodic aircraft sampling of greenhouse gases and meteorological conditions in the Los Angeles megacity during intensive campaigns.

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Methods

Measurement comments: Data included in this release: 1-hour average measurements of carbon dioxide and methane Year: 2015 Sites included: Compton, Fullerton, Granada Hills, Irvine, La Jolla, Ontario, San Clemente Island, USC, Victorville Additional details: Carbon dioxide (CO2) and methane (CH4) measurements are made on Picarro G2301 and G2401 wavelength-scanned cavity ring down spectroscopic instruments (Picarro Inc.). Carbon monoxide (CO) measurements are made on Picarro G2401 analyzers (see README). Each Picarro G2301 and G2401 site is equipped with 2 tanks calibrated on the WMO scale by NOAA/ESRL for CO2 and CH4 in the near-ambient range. Air from the calibration gases and air inlets are dried with a Nafion dryer as described by Welp et al., (2013). The calibration tanks are run approximately every 23 hours. One tank is assigned as the standard and the other as a target tank. The daily standard measurements are used for drift correction of the raw Picarro data. Beginning in 2014, high concentration (span) calibration gases were installed at all Picarro G2401 sites (measuring CO2, CH4 and CO) and some Picarro G2301 sites (measuring CO2 and CH4). In future revisions, the span tanks will be used to assess instrument non-linearity of the Picarro analyzers at greenhouse gas enhancements similar to those expected in the LA urban atmosphere. The raw sampling frequency of the Picarro instrument is approximately every 2-3 seconds. The 2-3 second data is then averaged to 1-minute intervals and the 1-minute averages are then gap-filled and used to compute the 1-hour average, standard deviation, number of 1-minute average data points contributing to the 1-hour average, and the maximum and minimum of the 1-minute average measured values. Hourly data are assigned to the top of each hour for both towers and rooftops. If less than five minutes of data remain in any 1-hour period (e.g., due to known technical or instrument errors) then NaN is reported. Some tower sites have measurements at multiple heights and hourly average data are reported from all inlet heights available. Rooftops sites are equipped with 4 air inlets and weather stations on each corner of the building. For rooftops, hourly average observations are reported using two different methods: 1) Using all available observations collected from the 4 corners within a 1-hour period; 2) Using only the "upwind" minutes measured within each 1-hour period, where "upwind" measurements were determined using the wind speed and direction measurements on each corner of the building. Hourly average mole fractions from rooftop sites calculated using other analysis methods may be available upon request. Measurement uncertainty estimates are underway, as detailed by Verhulst et al. (2017). In this revision, we report the uncertainty as the RMS error (U_tgt). U_tgt is based on tracking of the target tank, which is only one component of the overall analytical uncertainty described in Verhulst et al. (2017) and therefore represents the minimum analytical uncertainty of the air data. The standard deviation of the measurement during each 1-hour period is also reported and may be useful for characterizing the atmospheric variability within each 1-hour period. The towers and rooftops are also equipped with meteorological stations from Earth Networks, Inc. (https://www.earthnetworks.com/products/pulseapi/). Weather data includes the following variables: ambient temperature (degrees C), dewpoint temperature (degrees C), ambient pressure (millibar), wind speed (meters/second), and wind direction and is available upon request.

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Related Publication: Carbon dioxide and methane measurements from the Los Angeles Megacity Carbon Project – Part 1: calibration, urban enhancements, and uncertainty estimates Kristal Verhulst NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; University of California, Los Angeles, Joint Institute for Regional Earth System Science and Engineering, Los Angeles, CA. Anna Karion National Institute of Standards and Technology (NIST), Gaithersburg, MD Jooil Kim Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA Peter Salameh Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA Ralph Keeling Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA Sally Newman California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA; now at: Bay Area Air Quality Management District, Planning and Research Division, Climate Protection Section, San Francisco, CA John Miller NOAA/ESRL/GMD, Boulder, CO; CIRES, University of Colorado, Boulder, Boulder, CO, USA Christopher Sloop Earth Networks, Inc., Germantown, MD Thomas Pongetti NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Preeti Rao NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; now at: University of Michigan, School of Natural Resources and Environment, Ann Arbor, MI Clare Wong California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA; now at: California State University, Northridge, Institutional Research Office, Northridge, CA Francesca M. Hopkins NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; now at: University of California, Riverside, Department of Environmental Sciences, Riverside, CA Vineet Yadav NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Ray F. Weiss Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA Riley M. Duren NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Charles E. Miller NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA Atmospheric Chemistry and Physics 2017-07-07 https://doi.org/10.5194/acp-17-8313-2017 eng

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Contact person: Riley Duren Riley.M.Duren@jpl.nasa.gov

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