Smog chamber experiments were conducted to investigate the (1) kinetics of free radical reactions of SO2 in smog and (2) SO2 transformation to sulfate for atmospheric simulations. Rate constants were derived for the following reactions: SO2+HO+M yields sulfate (60), SO2+HO2 yields sulfate (61), SO2+CH3O2 yields sulfate (64); k(60) = 1600 k(61 less than 0.2, k(64) less than 0.8 ppm min. Oxidation of SO2 by HO led exclusively to particulate sulfate. Even under favorable NOx conditions, particulate nitrate was not a product. Hydrocarbon mixtures typical of urban environments promoted SO2 oxidation faster than hydrocarbons selected to represent rural conditions. Maximum rates of SO2 oxidation occurred during periods of peak NO2 formation. SO2 oxidation rates for aged smog were 25-35% of the maximum values. Model calculations indicated that reaction 60 dominates sulfate production from SO2 in polluted air. Models that adequately estimate (HO) in smog should suffice to approximate the conversion rates. The model used in this study indicated that SO2 oxidation depends strongly on solar radiation intensity and pollutant conditions. For clear-sky and a variety of HC-NOx conditions, maximum SO2 conversion rates ranged from 3.7-7.4%/hr. Models used to simulate reactions in power plant plumes showed that SO2 oxidation is strongly dependent on plume dispersion rates coupled to the same parameters governing SO2 oxidation in ambient air. Generally the rates of SO2 oxidation in plumes are bound by the ambient rates, although exceptions will occur for certain HC-NOx conditions.

Caption title. "Jun. 1981." "EPA-600/3-81-040." Microfiche.