The spatial distributions of precipitation acidity and major ion wet deposition in North America during 1980

Abstract

Observations are presented of the mean annual concentration and deposition of H⁺, SO₄ NO^-₃ and NH⁺₄ ions in precipitation in North America during 1980, the first year that a reasonably compatible merger of US and Canadian federal network data was possible. The maximum concentration and wet deposition of H⁺, SO⁼₄ and NO^-₃ occurred in-and south of-the great lakes region near maximum anthropogenic emissions of sulphur and nitrogen oxides. The NH⁺₄ maximum, however, was located in the north central US where American livestock feedlots are concentrated. Peak H⁺ concentrations were 60-80 μmole l^-1. In the region of maximum emissions, 1980 observations of H⁺, SO⁼₄ and NO^-₃ wet deposition are within 25% of the 5-year mean for 1977-1981. The respective fraction of anthropogenic sulphur and nitrogen oxides released in eastern North America that are wet deposited in the same area is 24 ± 6 and 25 ± 6%. On a smaller scale, in the high sulphur and nitrogen oxide emissions area of the northeastern US. the deposition was 13 and 18% of emissions, respectively. Trends in emissions as well as in SO⁼₄ and NO^-₃ concentrations in precipitation support the conclusion that a real increase in acidity of precipitation of 30-37 μmol l^-1 has occurred in the southeastern US since 1955/56.