J2.8
Study of the Photochemical Processes in the Houston-Galveston Metropolitan Airshed
Daewon W. Byun, University of Houston, Houston, TX
Compared with typical ozone evolution patterns in a clear summer day in other cities, several monitoring sites in the Houston-Galveston metropolitan area (HGA) show rapid transient high ozone events (THOEs) that significantly violate the U.S. National Ambient Air Quality Standards. The main culprit of this phenomenon is attributed to the ethylene and propylene emissions released from the petrochemical industries in the Houston Ship Channel. We investigate photochemical production of ozone by the highly reactive unsaturated hydrocarbons using modeling tools such as the MM5 meteorological model, SMOKE emissions processor, and EPA’s Models-3 CMAQ modeling system. The study targets to characterize CMAQ’s performance in identifying THOEs with current model configuration and input data, to compare different emissions inventories, and to study chemistry representation differences between Carbon-Bond 4 (CB-4) and SAPRC-99 chemical mechanisms. A few preliminary results are: (1) Meteorology is complex and has a significant impact on ozone formation. The primary meteorological pattern that leads to high ozone concentrations is associated with the land breeze in the morning that carries ozone precursors into Galveston Bay and the sea breeze in the afternoon that brings back the pool of high ozone concentrations across the city. (2) Ozone production rates in the Houston industrial plumes can exceed 50 ppb per hour. The rapid and efficient production appears to be the result of co-located large emissions of NOx and olefin emissions from industrial facilities. (3) There are very significant underestimations of the olefin emissions from the industries. It is supported by both the aircraft measurements during the TexAQS 2000 and emissions sensitivity study with the numerical model. .
Joint Session 2, Air Quality in Megacities (Joint with the Symp on Planning, Nowcasting and Forecasting in the Urban Zone and Sixth Conf on Atmospheric Chemistry; Room 612)
Tuesday, 13 January 2004, 8:30 AM-4:45 PM, Room 612
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