Significant emissions of NOx and SOx are released from point sources with tall stacks. These primary species are important precursors of a variety of secondary pollutant species, such as ozone and aerosols. The plume-in-grid (PinG) approach integrated in the Community Multiscale Air Quality (CMAQ) modeling system was designed to provide a realistic treatment of the physical and chemical processes affecting pollutant concentrations in isolated, major point sources plumes. In contrast to the traditional Eulerian grid modeling method of instantly diluting point source emissions into an entire grid cell volume, the PinG algorithms simulate the gradual horizontal and vertical growth of subgrid scale plumes and more properly treat the temporal evolution of photochemistry in individual plume-resolved cells during a subgrid scale phase within the CMAQ/Chemical Transport Model (CTM).

The PinG treatment has been extended recently with the incorporation of the same aerosol module already employed in the CMAQ/CTM Eulerian grid model. Consequently, gas-phase chemistry and aerosol processes can now be performed concurrently in the PinG submodel. Simulations are performed for a group of major point sources exhibiting a range of NOx and SOx emission rates situated in the greater Nashville, TN region. Due to the linkage between gases and aerosols, model runs are being conducted with two different sets of chemical mechanisms (Carbon Bond IV and RADM2) and chemical solvers (Gear and quasi-steady state approximation (QSSA)) to explore the impact on concentrations of aerosol sulfate and other aerosol species. Differences in aerosol concentrations for the wide range of emission rates will be examined. Additionally, a limited comparison of modeled results for selected gas species and aerosol concentrations will be presented against plume data obtained from research aircraft flights during the Southern Oxidant Study (SOS) field experiments in July 1995.