Input data for photochemical modeling of urban ozone in Monterrey, Mexico

This paper describes the input data used to evaluate the performance of a photochemical urban model with the environmental and geographical characteristics of the Monterrey Metropolitan Area. For the period 1993 through 1995, the Mexican ozone standard (110 ppbv) was exceeded on 63 days. This paper focuses on the application of a photochemical model to two high-ozone episodes in 1995: January 9-11 (winter episode) and July 3-5 (summer episode). Episode selection and inputs to the model were based on a review of available air quality, meteorological, and emission data. The model results show that the ozone concentrations are well-predicted for the summer period while they are underpredicted for the winter event. In addition, ozone is more sensitive to the variation of reactive hydrocarbon emissions in the winter. These results suggest that characterization of the diurnal pattern of industrial and vehicle emissions of reactive hydrocarbons needs to be improved. Also, the hourly differences in concentrations indicate that mountain-valley circulation may be a significant factor in ozone formation driven by recirculation of air pollutants. The emission inventory and ambient concentration data for Monterrey in the period 1993 through 1995 indicate that carbon monoxide emissions have decreased, while nitrogen oxides emissions remained constant. Also, these data suggest that hydrocarbon emissions may have decreased. However, the aromatic content in the reactive hydrocarbon emissions may be higher due to the recent introduction of gasoline additives.