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NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
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Industrial Hydrocarbon Emission Adjustments Used in 2002 Houston-Galveston-Brazoria Ozone SIP Modeling
Jim Smith, Doug Boyer, Mark Estes, Gabriel Cantu, Ron Thomas
Texas Commission on Environmental Quality
The Texas Air Quality Study (TexAQS) was one of the largest and most comprehensive air quality studies ever conducted. Approximately 250 researchers from over 35 institutions joined the TCEQ to collect data from the period August 15 - September 15, 2000, primarily in the Houston/Galveston/Brazoria ozone nonattainment area of the Upper Texas Coast. Air quality and meteorology were sampled at several locations, and a total of six research aircraft participated in the study. While the study yielded (and has in fact continued to yield) an enormous amount of information related to air quality in the study region, perhaps the most remarkable finding is that the atmospheric concentrations of light olefins are many times higher than can be explained from the reported emissions of these compounds. Furthermore, aircraft observations clearly associated these very high olefin concentrations with industrial sources in the area. Light olefins, particularly ethylene and propylene, are extremely reactive photochemically and are believed to contribute significantly to the rapid rises in ozone concentrations and extremely large peak concentrations which occur frequently in the airshed.
The TCEQ Modeling staff modeled an ozone episode from the TexAQS period for a State Implementation Plan (SIP) revision which was approved on December 13, 2002. When photochemical grid modeling was conducted using an emissions inventory compiled employing routine methods, peak ozone was severely under-predicted almost universally throughout the episode. Based on the TexAQS conclusions and additional aircraft measurements, an adjustment was applied to the industrial emissions of a group of highly-reactive compounds (principally olefins). After applying this adjustment, model performance improved markedly and the TCEQ was able to develop a coherent picture of the ozone formation processes taking place during the TexAQS time frame. In this presentation, the authors describe the photochemical modeling conducted and discuss the effects of adjusting the emissions on the model outcome.