Plume-in-grid modeling for particulate matter

Three-dimensional grid models are now being commonly used to simulate particulate matter (PM) concentrations, especially fine PM (PM2.5), which includes a significant fraction of secondary species formed in the atmosphere. These models usually do not address the subgrid-scale effects associated with emissions from large elevated point sources. This can lead to errors in the calculation of PM2.5 concentrations downwind of these sources because of unrealistic representations of the dispersion and transformation processes that govern PM2.5 formation. Here, we describe the development, application and evaluation of a plume-in-grid (PiG) model for PM. The model, based on an existing PiG model for ozone, is extended to include in the plume component state-of-the-science treatments of aerosol chemistry and dynamics as well as aqueous chemistry that are consistent with the treatments used in the host grid model. Application of this model to several SO2 and NOx emitting power plants in the southeastern United States shows that the PiG treatment leads to significant differences in sulfate and total inorganic nitrate concentrations. Comparisons of model results, with and without PiG treatment, against measurements characterizing specific plume events, show that the PiG treatment captures the plume events more often and generally better than the standard grid-based approach.