Issues on Urban Ozone: Natural Hydrocarbons, Urbanization and Ozone Control Strategies.

Using the Atlanta metropolitan area as a case study, we have examined the effects of urbanization and its associated heat island on urban ozone concentrations. As cities grow, two important effects take place: the amount of trees is reduced and there is an increase in ambient temperature due to the urban heat island effect. As the temperature increases, more ozone is photochemically produced, more anthropogenic hydrocarbons are released into the atmosphere, and more biogenic hydrocarbons are emitted from the remaining trees. This increase in hydrocarbons helps produce even more ozone. Numerical simulations using conditions of a typical summertime day in Atlanta suggest that these processes are able to offset the reductions in anthropogenic hydrocarbon emissions caused by emission controls. To study ozone control strategies, we have developed a photochemical model that utilizes ozone and ozone precursors observations as input data, and is therefore independent of the highly uncertain processes of emission inventories and transport. In contrast with the operation of the current emission-based models, the observation-based model (OBM) is relatively easy to implement and very fast to operate. Using numerical simulations of different meteorological and chemical conditions in Atlanta, we have shown that the ozone sensitivities obtained with the observation-based model, are in very good agreement with similar ozone sensitivities derived using an emission-based model that includes transport. We also illustrated the potential utility of the OBM by applying it to the ozone non-attainment problem in Baton Rouge, Louisiana. The results of these calculations suggest the need for a serious reassessment of current ozone abatement strategies.