Aqueous phase atmospheric oxidation of sulfur dioxide by oxygen: Role of trace atmospheric constituents - Metals, volatile organic compounds and ammonia

The oxidation of dissolved sulfur dioxide, i.e. sulfur(IV) by oxygen is an important pathway in the acidification of atmospheric waters. Over the years, much work has been done in our laboratory on this important atmospheric reaction. The catalytic role of transition metal ions, viz. Fe-III, Mn-II, Cu-II, Ni-II, Ag-I, Os-VIII and Pd-II has been examined. The role of surface catalysis on this reaction in suspensions of CoO, C2O3, CuO, Cu2O, MnO2, Ni2O3, CdO, CdS, MgO, SiO2, PbO2, free fall atmospheric dust, fly ash, rock and mineral powders, lime stone etc. has been examined. It was shown for the first time that ammonia and ammonia ions - important trace atmospheric constituents - inhibit the oxidation of dissolved SO2 if pH >= 7 and [NH3](T) exceeds a particular value (similar to 5 x 10(-5) mol L-1).