Industrial emissions cause extreme urban ozone diurnal variability

Simulations with a regional chemical transport model show that anthropogenic emissions of volatile organic compounds and nitrogen oxides (NOx = NO + NO2) 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 NOx 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 NOx 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.