In this article, we argue that aqueous phase oxidation of SO2 is the major source of precipitation sulfate. Based on this conclusion, we examine the relationship of sulfur emissions to sulfate in precipitation using two models. A climatological macroscopic model of the regional sulfur balance in the eastern United States (EUS) is used to infer the probability with which SO2 is oxidized and deposited as sulfate in precipitation. A microscopic model based on aqueous phase oxidation by H2O2 in droplets and derived from recent precipitation and in-cloud measurements is used to explore the response of oxidation at the molecular level to changes in ambient SO2 concentrations. The result of the macroscopic model demonstrates that SO2 emitted in the EUS and processed through precipitating air parcels is oxidized and deposited in precipitation on land in eastern North America (ENA) with relatively high probability (> 73 per cent) based on regional sulfur measurements for 1977-1979. Using an oxidant-limited model for SO2 oxidation, quantitative limits are derived for the response of wet sulfate deposition to emissions reductions, and it is inferred that a 50 per cent emissions reduction would have produced significant reductions (probably > 40 per cent) in precipitation sulfate originating in EUS emissions and deposited on land in ENA during the relevant period.
All Science Journal Classification (ASJC) codes
- Environmental Science(all)
- Earth and Planetary Sciences(all)