Industrial emissions cause extreme urban ozone diurnal variability

Abstract

Simulations with a regional chemical transport model show that anthropogenic emissions of volatile organic compounds and nitrogen oxides (NO(x) = NO + NO(2)) lead to a dramatic diurnal variation of surface ozone (O(3)) in Houston, Texas. During the daytime, photochemical oxidation of volatile organic compounds catalyzed by NO(x) results in episodes of elevated ambient O(3) levels significantly exceeding the National Ambient Air Quality Standard. The O(3) production rate in Houston is significantly higher than those found in other cities over the United States. At night, a surface NO(x) maximum occurs because of continuous NO emission from industrial sources, and, consequently, an extensive urban-scale "hole" of surface ozone (<10 parts per billion by volume in the entire Houston area) is formed as a result of O(3) removal by NO. The results suggest that consideration of regulatory control of O(3) precursor emissions from the industrial sources is essential to formulate ozone abatement strategies in this region.