A study of VOC reactivity in the Houston-Galveston air mixture utilizing an extended version of SAPRC-99 chemical mechanism

The Houston-Galveston area is the region where National Ambient Air Quality Standard (NAAQS) for ozone is often violated. Emissions from industrial sources contribute significantly to elevated ozone concentrations and make air composition quite unique in comparison to typical urban composition. In this study, source-oriented reactivity of individual organic compounds, released in urban and industrial areas inside Houston-Galveston region, with regard to ozone formation is determined. The CMAQ model and an extended version of SAPRC-99 mechanism, representing 26 additional individual compounds explicitly, is employed for the model simulations. The incremental volatile organic compound (VOC) reactivities calculated for the Houston-Galveston conditions show variations with respect to the differences in the air compositions between urban and industrial areas as well as meteorological conditions. The compounds with the highest reactivities, such as 2-methyl-2-butene, trans-2-butene and cis-2-butene, were found to be most sensitive to the environment in which they were released. According to the reactivities weighted by VOC mixing ratios, ethene, propene and formaldehyde show the highest impact on ozone formation. Reactivities of most investigated compounds estimated for the Houston-Galveston air conditions are in good agreement with the ‘reference’ maximum incremental reactivity (MIR) scale.