Chemical Coupling between Ozone and Particulate Matter under Different Meteorological Conditions

Ozone and particulate matter controls are traditionally considered separately because their high pollution periods generally are not concurrent. O3 concentrations are high in the summer and PM2.5 concentrations are high in the winter. California's San Joaquin Valley has serious ozone and fine particulate matters air pollution problems due to its unique geography and its diverse emission sources from local and upwind areas. Observations and modeling studies of the air quality in this region have found a strong tendency for both pollutants to form and/or increase together during the summer time. Since a major fraction of fine particulates forms from atmospheric gas-to-particle conversion, attempts to reduce PM2.5 will require control of the same volatile organics (VOC) and nitrogen oxides (NOx) emissions that are also precursors to ozone formation. The chemical coupling between ozone and particulates is important for understanding processes that control the levels of both. In this study, we apply CMAQv4.7.1 to modeling a two month period in the summer of year 2000 for the central California region for a variety of emission and meteorological conditions. Simulations are conducted under the base emission case and for various precursor emission reduction cases (for volatile organic compounds and nitrogen oxides). Results are highlighted for selected meteorological regimes when both high PM and high ozone occur. The influence of chemical coupling between the ozone and particulate production is illustrated by the spatial distributions of pollutant responses to emission reductions.