Evaluation of air quality models for the simulation of a high ozone episode in the Houston metropolitan area |
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| Institution: | 1. Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA;2. St. Edward''s University, School of Natural Sciences, Austin, TX, USA;4. New Mexico Tech, Department of Physics, Socorro, NM, USA;5. National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD, USA;1. Pasture Systems and Watershed Management Research Unit, USDA Agricultural Research Service, University Park, PA 16802, USA;2. Department of Biological and Agricultural Engineering, Kansas State University, Manhattan, KS 66506, USA;3. National Laboratory of Agriculture and the Environment, USDA Agricultural Research Service, Ames, IA 50011, USA;4. Bayer Crop Science, 2 T.W. Alexander Dr., Research Triangle Park, NC 27709, USA;1. Department of Meteorology, The Pennsylvania State University, University Park, PA 16802, USA;2. Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, USA;1. National Centre for Atmospheric Science, Centre for Atmospheric & Instrumentation Research, University of Hertfordshire, Hatfield, UK;2. Centre for Atmospheric & Instrumentation Research, University of Hertfordshire, Hatfield, UK;3. Environment Agency, Reading, UK;4. Met Office, Hadley Centre, Exeter, UK;5. Colorado State University, Fort Collins, CO, USA;6. Department of Meteorology, University of Reading, Reading, UK;1. School of Atmospheric Sciences, Nanjing University, Nanjing, 210093, China;2. School of Environmental Sciences and Engineering, Sun Yat-sen University, Guangzhou, 510275, China |
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| Abstract: | A high ozone event in the Houston–Galveston–Brazoria area was utilized to study the shortcomings of the current air quality models. To improve the baseline simulations with the Comprehensive Air quality Model with Extensions (CAMx) for developing the state implementation plan, the Texas Commission on Environmental Quality (TCEQ) imputed emissions of highly reactive volatile organic compounds (HRVOCs) by scaling the amount of fugitive emissions of olefins to co-emitted NOx from selected point sources, effectively multiplying by 3–12 times over the regular inventory values. In this paper, CAMx and the Community Multiscale Air Quality (CMAQ) model were used to determine if the imputed HRVOC emissions were consistent with the observed atmospheric conditions. With the base emissions, CMAQ and CAMx both with the Carbon-Bond 4 (CB-4) mechanism simulated similar ozone concentrations. But with the imputed HRVOC emissions, CMAQ predicted lower ozone peaks than CAMx in the vicinity and downwind of the Ship Channel and other highly HRVOC-rich areas. Based on analyses of sensitivity simulations of CMAQ with different emission inputs and vertical diffusion algorithms in the model, we found that the modeled atmosphere lacked reactivity to produce the observed high ozone event. Although the imputed HRVOC emissions improved ozone prediction at the surface sites, but the ethylene concentrations were not consistent with the measurements at the super sites (La Porte and Clinton) and by NOAA aircraft. Several sensitivity tests designed to provide additional radicals into the system and other research results suggested that the lack of reactivity may need to be corrected by targeted, and probably of episodic, increase of HRVOC emissions, from the sources in the Houston Ship Channel. Additional investigation of the ozone production efficiency for different chemical mechanisms is necessary to pinpoint the emissions uncertainty issues. |
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