SO2 OXIDATION AND H2O-H2SO4 BINARY NUCLEATION BY RADON DECAY

The oxidation of SO2 by . OH radical produced by radon decay and binary nucleation of H2SO4-H2O were studied using a thermal diffusion cloud chamber. A kinetic model was developed to examine the oxidation of SO2 by . OH to H2SO4 to estimate airborne concentration of the critical species. The kinetic modelling calculations suggested that . OH radical production is the rate control step among the gas-phase reactions proposed. The experimental results showed that nucleation rates increase with increasing radon and SO2 concentrations. Two distinct types of nucleation, mist and rain, were observed at different supersaturation in the thermal diffusion cloud chamber. The experimental observations suggest that both SO2 and H2SO4 can cause binary nucleation with water vapor. It is necessary to further distinguish between these two nucleation mechanisms in the future in order to obtain a better understanding of this combined oxidation and nucleation mechanism.