03/30/2017   Simulation of Carbonyl Sulfide (COS) to better understand the urban biosphere signal by Gara Villalba University of California, Merced. April 5, 2017

UC Merced Environmental Systems Seminar Wednesday, April 5, 2017 12:30-1:50 pm, COB 114 Generally, top-down approaches to estimate anthropogenic CO2 emissions over urban regions rely on subtracting the Net Ecosystem Exchange (NEE) CO2 from observation (measured) CO2 data. However, the offsetting photosynthesis and respiration components that make up NEE introduce a high degree of uncertainty in these calculation. We suggest that COS can be used to constrain the photosynthetic uptake of CO2 to more accurately determine the fossil CO2 component in urban regions. Just like CO2, COS is taken up by photosynthesis but is not given off in respiration and can thus be used as a trace gas to estimate GPP. We use COS surface fluxes provided by various biosphere models regridded for the Bay Area of San Francisco which serves as the case study region. Simulations using the atmospheric model WRF provide the meteorological data, which along with the COS fluxes, are used to run a chemical transport model over a 20-day period in March 2015. Simulations of COS mixing ratio based on the various surface flux models are compared to observed data available from several observation towers. The model that best represents COS uptake consequently also provides the most accurate simulation of the CO2 biosphere signal, and can be used to estimate fossil fuel CO2 emissions.

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