THE IMPACT OF CHANGING REGIONAL EMISSIONS ON PRECIPITATION CHEMISTRY IN THE EASTERN UNITED-STATES

From 1975 to 1987 a 19% change in SO2 emissions and a 16% change in NO(x) emissions have occurred over the eastern and mid-western U.S. Six continental precipitation chemistry sites from the MAP3S network, plus the Hubbard Brook Experimental Forest, NH, show a direct relationship between emission levels and precipitation H+ and SO4(2-) concentrations, except for Penn State, PA. MAP3S sites at Illinois and Ohio, located closest to the major SO2 source regions, demonstrate statistically significant (P < 0.05) linear regressions of SO4(2-) concentrations on SO2 emissions. Whiteface Mt., NY, shows a weaker relationship (P < 0.10), and Hubbard Brook shows the strongest relationship (P < 0.01) between SO2 emissions and SO4(2-) concentration in precipitation. No site shows a significant relationship (P < 0.10) for NO(x) emissions and NO3- concentrations in precipitation. Illinois, Ohio, Ithaca and Hubbard Brook show significant linear regressions of H+ concentrations on emissions of SO2 + NO(x) (P < 0.10, 0.05, 0.01, and 0.01, respectively). Overall, for the entire region examined, decreasing SO2 emission levels appear to have decreased SO4(2-) concentrations with an efficiency of 74% +/- 15% (s.e.). Decreasing SO2 plus NO(x) emissions (18%) have been accompanied by a decreasing H+ concentrations (18%) suggesting an efficiency of conversion of 100% +/- 15% (s.e.) for the study region as a whole. While significant reductions in acid species have occured at Hubbard Brook, further reductions in excess of 50% of present deposition are necessary to protect acid-sensitive ecosystems.