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U.S. Environmental Protection Agency Region 6 Dallas, Texas, USA By Melody Lister (Lockheed Martin) and Mark Sather (EPA) Contact Mark Sather Software ArcGIS Desktop 9.2 Printer HP Designjet 5500 ps Data Sources U.S. Environmental Protection Agency, U.S. Census Bureau, National Oceanic and Atmospheric Administration 28 Environmental Management The U.S. Environmental Protection Agency (EPA) Region 6 needs to analyze regional pollution to better understand the ozone problem in key areas. This map assists in the study by showing the spatial relationship between major nitrogen oxides (NOx) stationary emission sources, ambient ozone concentrations, ambient NOx and volatile organic compounds (VOC) precursor concentrations, population density, and 24-hour wind back trajectories on high ozone concentration days. The back trajectories, created using the National Oceanic and Atmospheric Administration’s Hysplit Model, help identify possible source areas of the contaminant. This enables EPA Region 6 to target areas for ozone reduction more efficiently. As shown here, none of the monitors in the Houston area met the 2008 8-hour ozone standard of 0.075 ppm. Ozone design values range from 0.076 ppm at Lake Jackson in southwestern Brazoria County to 0.096 ppm at Bayland Park west of downtown and the Ship Channel. The higher ozone concentrations in the western part of Houston are supported by the predominance of east sector wind flow on the highest ozone concentration days. Courtesy of U.S. Environmental Protection Agency Region 6. Houston Ozone and Ozone Precursor Monitoring Network