On the Mechanism of Sulfur Dioxide Oxidation in Cloud Drops

Data from field experiments on the dynamics of SO2 oxidation in cloud droplets are presented. The rapid experimentally observed oxidation of SO2 by molecular oxygen is attributed here to the catalytic action of a pair of manganese and iron ions in droplets. Their effect, inhomogeneous in the drop-size distribution and attributed in experiments only to the leaching of ions of these metals from coarse particles of mineral aerosol, is also caused by the transition of the oxidation reaction into the branching mode. The results indicate that the branched regime of catalytic oxidation of SO2 detected in cloud droplets should be considered a new and significant source of sulfates in the atmosphere. This process must be taken into account when considering both the budget of sulfates in the global atmosphere and their impact on the climate.