A chamber study of catalytic oxidation of SO2 by Mn2+/Fe3+ in aerosol water

The catalytic oxidation of SO2 by metal ions in aerosol water may be one of the important sources of sulfate in the atmospheric environment. In order to better understand the catalytic oxidation in aerosol water, a series of experiments were carried out in a smog chamber system under the conditions of relatively low concentrations of SO2 with Mn2+/Fe3+ as catalysts in NaNO3 aerosol water. In the Mn2+-catalytic oxidation process, the reaction rate (R) in aerosol water is expressed as R = 2.0 x 10(4) [Mn2+][S(IV)](1.3) at the initial pH range 4-5, which is about 2 orders of magnitude higher than that in bulk water. When the pH of aerosol water and relative humidity (RH) are high, the catalytic oxidation of SO2 by Mn2+ in aerosol water is probably an important source of sulfate. In the Fe3+-catalytic oxidation process, the reaction rate is significantly lower than that of Mn2+-catalytic oxidation, and the rate hardly exceeds 2 orders of magnitude larger than that in bulk water. The role of synergistic catalysis between Fe3+ and Mn2+ for oxidation of SO2 in aerosol water is very limited.