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 super-saturation 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.