DEVELOPMENT AND APPLICATION OF A NEW AIR-POLLUTION MODELING SYSTEM .2. AEROSOL MODULE STRUCTURE AND DESIGN

The methods used for simulating aerosol physical and chemical processe s in a new air pollution modeling system are discussed and analyzed. S uch processes include emissions, nucleation, coagulation, reversible c hemistry, condensation, dissolution, evaporation, irreversible chemist ry, sedimentation, dry deposition, and radiative scattering and absorp tion by particles. A new particle size bin structure that nearly elimi nates numerical diffusion during growth but still treats nucleation, e missions, coagulation, and transport realistically is discussed. In ad dition, coagulation is shown to reduce the number and volume concentra tion of particles less than 0.2 mu m in diameter both in the presence and absence of modest rates of particle growth. However, when signific ant growth occurs, the effect of coagulation is reduced. Further, whil e sulfate production due to SO2 dissolution and oxidation in cloud dro ps is confirmed to be important, it is shown here that such production in aerosols is small over time periods simulated in urban air polluti on models. Finally,light scattering and absorption coefficient predict ions, obtained by applying a Mie code for stratified spheres, are disc ussed and shown to match data for a given scenario. Remaining processe s in the aerosol module are described. Copyright (C) 1996