Abstract
This paper describes the use of a regional-scale air quality model as a diagnostic tool for analyzing problems associated with acid rain. The model, which is hybrid in nature, consists of a puff module and a grid module. The puff module computes the evolution of individual puffs, such as the horizontal and vertical standard deviations of the puff spreads and the location of the center of mass, emitted continuously from each major point source. It also determines the location at which the puff will be released to the grid module and the amount of oxidation and deposition along the trajectory. The grid module then follows the transport, diffusion, and chemical reactions of these aged puffs, as well as emissions from a variety of diffuse sources. Elaborate schemes for both dry and wet deposition have also been incorporated into the model. This model has been exercised for two real-time meteorological scenarios—a dry case and a two-day rainstorm episode in the Northern Great Plains. On the basis of model calculations, atmospheric budgets for SO2 and sulfate over the modeling region have been estimated.
