SULFUR-DIOXIDE IN COASTAL NEW-ENGLAND FOG

During six fog events in the year 1990, we investigated the concentration and oxidation capacity of SO2 at a sampling site on the coast of New England. The SO2 mixing ratio was usually in the range of a few parts per billion, and its variability during a single event was governed mostly by changes in air masses of different history and overall chemical composition, rather than chemical oxidation in cloud. Although the H2O2 mixing ratio was low during the foggy periods, it dominated the oxidation of SO2. Ozone and manganese- and iron-catalysed reactions play minor roles. The overall oxidation capacity for SO2 was low in most cases (< 2% h-1), probably because the oxidation of SO2 by H2O2 was completed before the fog droplets were collectable. In one case with low SO2 mixing ratios (< 1 ppb), the oxidation intensity of SO2 was intense (40% h-1).