Sulfur and associated elements and acidity in continental and marine rain from north Florida

Rainwater was sampled for every rainfall occurrence between November 7, 1978, and January 26, 1979, in Tallahassee, Florida, a generally unpolluted area in the southeastern United States, about 50 km north of the Gulf of Mexico. The elemental composition was determined for 12 elements, S, K, Ca, V, Mn, Fe, Ni, Cu, Zn, Br, Sr, and Pb, by proton-induced X ray emission from 4 ml aliquots of 38 different rain samples. The elemental composition of the rain was found to be different for rain associated with northerly and southerly air flow regimes. In north air flow rain, originating from more polluted northern areas, concentrations of Pb, S, and Fe were higher and strong correlations of Br, Ca, and Fe with Pb were observed. Thus the north air flow rain exhibits polluted and continental characteristics. On the other hand, most elemental concentrations were lower in south air flow rain originating in the Gulf of Mexico, and strong correlations between elements such as S, K, Ca, and Br, but not with Pb, were observed. These results indicated a strong influence by sea spray. The north and south air flow rains also differed significantly in their acidity. In northern rain the average pH was 4.4 with a minimum of 3.7, whereas in southern rain the average pH was 5.3 with a minimum of 4.6. A strong correlation between pH and logarithmic sulfur concentration was observed in northern rain but not in southern rain. This suggests that most of the sulfur in northern rain is sulfuric acid transported from pollution sources, whereas southern rain includes much neutralized seawater sulfate.