Mathematical Modeling of Atmospheric Aerosol Equilibria and Dynamics

Atmospheric aerosols consist of submicron-sized particles occurring at number concentrations of the order of 105 cm-3 and mass concentrations of the order of 100 µg m-3. These aerosols, when occurring in urban areas, consist of aqueous solutions of sulfate, nitrate, ammonium, organic constituents, and certain metals. This thesis is a contribution toward our ability to describe mathematically the formation and growth of such atmospheric aerosols. Since a substantial fraction of the mass of urban aerosols consists of sulfate, nitrate, ammonium and water (Stelson and Seinfeld, 1981), the description of the dynamics of such an aerosol is an important place to initiate the development of aerosol models. The size and composition distribution of atmospheric aerosols are governed by a combination of thermodynamics and kinetics. A detailed treatment of the thermodynamics of the atmospheric sulfate/nitrate/ammonium/water system is presented. Based on this treatment, models are developed to predict the equilibrium quantity, composition, state, and size of the aerosol given gas phase properties. Aerosol kinetics are approached by solution of the General Dynamic Equation for the aerosol sized distribution using the sectional method of Gelbard and Seinfeld. In the most general kinetic model presented, the evolution of the size and composition of an atmospheric sulfate aerosol is predicted under power plant plume conditions. Users manuals for the computer codes comprising the models developed here are given in the Appendix.