The Chemical composition of atmospheric precipitation in Minnesota and North Dakota

Precipitation chemistry in central North America appears to be controlled by interaction between soil derived alkaline dust and gaseous NH3 from the cultivated prairie and anthropogenic acid aerosols from the urban industrial Lower Great Lakes Ohio Valley region. Analyses of major ions and trace metals in precipitation event and snow core samples along a 600 km transect from the North Dakota prairie to the northeastern Minnesota forest indicate that loadings and concentrations of soil derived materials decrease with increasing distance from the prairie. Acidity is highest in the east and decreases to the west. Sulfate has natural sources in the west and anthropogenic sources in the east; its concentration was least at sites in the middle of the transect. Acidity increased and inputs of soil derived elements decreased during winter when snow and freezing temperatures reduced alkaline influxes to the region.