Determining the climatology of ozone potential for the U.S.-Mexico border

Ozone pollution in the United States-Mexico border region is increasing due to growth and development of urban and industrial centers on both sides of the international boundary. Ambient ozone concentrations are influenced strongly by atmospheric circulation, which varies considerably Over the US-Mexico borderlands. Concerns have arisen regarding the potential for ozone formation near current and future areas of high precursor emissions. Ozone potential depends on the range of weather patterns that move over the area in question, and thus a sound understanding of climatological controls on border-region ozone is required. This study uses an existing synoptic climatology to analyze a range of ozone data from the borderlands. The regional, or synoptic, scale is the primary weather-system scale controlling border region climate, especially those variables affecting air quality. The synoptic climatology comprises six characteristic circulation patterns based on gridded 850 mb pressure-height data from 1963 to 1994. The synoptic catalog is combined with surface weather data for sites located throughout the region. Ozone data for varying lengths of record from the mid-1970s to 1994 were extracted from the EPA AIRS database and other available sources. Relationships between circulation patterns, weather conditions and ozone were determined by statistical modeling. Results show that the border region is differentially susceptible to high-ozone weather conditions. Associated suites of weather variables influence ambient ozone concentrations under each circulation pattern, resulting in a spatially and temporally distinct 'ozone footprint' for the region. Climate data are more readily generalized than site-specific ozone data, and thus climate-related potentials for ozone pollution are inferred for unmonitored areas of the US-Mexico border region.