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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-254
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Sep 2018

Research article | 12 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Quantification of CO2 and CH4 emissions over Sacramento, California based on divergence theorem using aircraft measurements

Ju-Mee Ryoo1,2, Laura T. Iraci1, Tomoaki Tanaka1,b, Josette E. Marrero1,c, Emma L. Yates1,3, Inez Fung4,5, Anna M. Michalak6, Jovan Tadić6,a, Warren Gore1, T. Paul Bui1, Jonathan M. Dean-Day1,3, and Cecilia S. Chang1,3 Ju-Mee Ryoo et al.
  • 1Atmospheric Science Branch, NASA Ames Research Center, Moffett Field, CA, 94035, USA
  • 2Science and Technology Corporation (STC), Moffett Field, CA, 94035, USA
  • 3Bay Area Environmental Research Institute, Moffett Field, CA, 94035, USA
  • 4Department of Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA 94720, USA
  • 5Department of Environmental Sciences, Policy and Management, University of California, Berkeley, Berkeley, CA 94720, USA
  • 6Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, USA
  • anow at: Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
  • bnow at: Japan Weather Association, Tokyo, Japan
  • cnow at: Sonoma Technology, Inc., Petaluma, CA, 94954, USA

Abstract. Emission estimates of carbon dioxide (CO2) and methane (CH4) and the meteorological factors affecting them are investigated over Sacramento, California, using an aircraft equipped with a cavity ring–down greenhouse gas sensor as part of the Alpha Jet Atmospheric eXperiment (AJAX) project. To better constrain the emissions fluxes, we designed flights in a cylindrical pattern and computed the emission fluxes from three flights using a kriging method and Gauss's divergence theorem.

The CO2 and CH4 mixing ratios at the downwind side of Sacramento show relatively consistent patterns across the three flights, but the fluxes vary – as a function of different wind patterns on a given flight day. The wind variability, seasonality, and assumptions about background concentrations affect the emissions estimates, by a factor of 1.5 to 8. The uncertainty is also impacted by meteorological conditions and distance from the emissions sources. The largest CH4 mixing ratio was found over a local landfill.

The importance of vertical mass transfer for flux estimates is examined, but the difference in the total emission estimate with and without vertical mass transfer is found to be small, especially at the local scale. The total flux estimates accounting for the entire circumference are larger than those based solely on the downwind region. This indicates that a closed-shape flight profile can better contain total emissions relative to one-sided curtain flight because most cities have more than one point source and wind direction can change with time and altitude. To reduce the uncertainty of the emissions estimate, it is important that the sampling and modeling strategy account not only for known source locations but also possible unidentified sources around the city. Our results highlight that aircraft-based measurements using a closed shape flight pattern are an efficient and useful strategy for identifying emission sources and estimating local and city-scale greenhouse gas emission fluxes.

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Short summary
We designed flights in a cylindrical pattern and computed the emission fluxes using a kriging method and Gauss's divergence theorem over Sacramento, California. The wind variability and assumptions about background concentrations affect the emissions estimates, by a factor of 1.5 to 8. The total flux estimates accounting for the entire circumference are larger than those based solely on the downwind region, indicating that a closed-shape flight profile can better contain total emissions.
We designed flights in a cylindrical pattern and computed the emission fluxes using a kriging...
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