The relationship between regional SO2 emissions and downwind aerosol sulfate concentrations in the northeastern US

Our research group has been continuously measuring aerosol sulfate at Whiteface Mountain, New York, since 1979 and at Mayville, New York, since 1984. Monthly aerosol SO2−4 concentrations for these sites are reported here through 1997. Seasonal and long-term profiles of SO2−4 are presented along with SO2 concentrations. As these sites are directly downwind of the high SO2 emission region in the Midwestern United States and the same sampling and analytical protocol has been maintained, they are ideally suited to evaluate long-term trends. The recent reductions in SO2 emissions in response to provisions of the 1990 Clean Air Act provide an excellent opportunity to evaluate the sulfur source–receptor relationship. A linear relationship is demonstrated between aerosol SO2−4 and total sulfur (ST, sum of S present as SO4 and SO2) concentrations at these sites and SO2 emissions upwind in the Midwest. This is the most direct evidence to date that deposition of sulfur in the Northeast is linearly related to upwind SO2 emissions. The results support the possibility of using the ratio of SO2−4/SO2 emissions to develop an empirical source–receptor relationship for the region.