Measurements of S(IV) and organic anions in minnesota rain

In 167 fractions from 84 rain events collected at two sites in Minnesota during the summer of 1982, S(IV) accounted 1.12% of the measured anions and thus usually contributed very little of the free acidity. A few events were observed, however, in which the S(IV) contribution was large. Organic acids were observed in nearly every fraction, with acetate being the most abundant. The samples were not preserved to prevent the loss of organic acids, which made an accurate assessment of the contribution of the organics to the acidity impossible and may have accounted for the low amounts of formate observed. The pH of samples in storage increased with time, a phenomenon which appeared to be related to gas exchange.