The effect of local emissions on wet and dry deposition in Southeastern Michigan

Abstract

Recent reports have suggested that local sources exert a strong impact on precipitation chemistry. This idea was tested at two sites in SE Michigan which have very different local emissions: near the urban site SO 2 emissions are 300 times higher, NO x emissions are 9 times higher, and TSP emissions are 56 times higher than near the rural site. Ambient particle concentrations, dry deposition, and wet deposition were monitored at the two sites for a period of 320 days. The urban site had significantly higher ambient particle concentrations of SO 4 2−(76% higher), NO − 3 (48%), Ca 2+ (107%), Na + (260%) and Cl − (480%). Dry deposition at the two sites reflected the differences in ambient concentrations. However, the wet deposition concentrations, when considered in terms of average concentrations, weighted averages, total wet flux, or on an individual storm basis, showed no significant differences between the two sites in pH, SO 4 2−, NO 3 −, or Ca 2+. The high local emissions near the urban site had no apparent effect on the precipitation chemistry based on these data.