Field evidence for the oxidation of SO2 by H2O2 in cap clouds

We have used a new experimental design to investigate the dominant oxidation pathways of SO2 in the conditions that occur in natural clouds. This involved modifying SO2 levels in capping cloud on a peak in the northern Pennine hills of England by releasing SO2 locally upwind and then measuring changes in cloud and air composition. Under the conditions encountered it was found that sulphate production by both ozone and H2O2 was negligible. The destruction of H2O2 by reaction with SO2, however, was clearly demonstrated. By comparing H2O2 in the presence and absence of released SO2, the rate of destruction was estimated and found to be comparable with that expected from laboratory measurements of the reaction rate constant, and our knowledge of the cloud physics. -from Authors