Photochemical aerosol formation from SO₂: A theoretical analysis of smog chamber data

A simplified theoretical model is proposed for evaluating the dynamic behavior of photochemically generated aerosols in the SO₂-air system. The key simplifying assumption is that evaporation rates are negligible compared with condensation rates for molecular clusters and particles of all sizes. The theory accounts for the formation of condensable molecules (monomer) by chemical reaction, and coagulation of these monomer with clusters of condensed molecules to form larger particles. Cluster coagulation is also included. For a constant rate of monomer production, the equations can be cast in a dimensionless form which is independent of the rate of monomer formation by chemical reaction. These dimensionless equations have been solved numerically, both including and neglecting the effect of London-van der Waals forces on the coagulation rate. Agreement between theory and the data ofW. E. Clark ("Measurements of Aerosols Produced by the Photochemical Oxidation of SO₂ in Air," Ph.D. thesis, University of Minnesota, Minneapolis, 1972) and G. Madelaine, M. Perrin, and A. Renoux (J. Aerosol Sci. 12, 202 (1979)) is good, particularly when London-van der Waals forces are considered. Because the solutions are presented in dimensionless form, direct application of these results for arbitrary rates of aerosol formation and for aerosols with arbitrary physical properties is possible.