Statistical Analysis of Precipitation Chemistry Measurements over the Eastern United States. Part IV: The Influences of Meteorological Factors

Abstract

The influences of meteorological factors on precipitation acidity and constituent concentrations were investigated statistically using selected portions of a new archive of daily precipitation chemistry measurements for the eastern United States. This archive consists of measurements from networks operated by the Electric Power Research Institute and Utility Acid Precipitation Study Program (EPRI-UAPSP), the Multistate Atmospheric Power Production Pollution Study (MAP3S), and the Wisconsin Acid Deposition Measuring Programs (WADMP) during the period 1979 through 1983. Differences in acidity and analyte concentrations were found for different precipitation types. Rain had significantly higher average acidity, and higher sulfate and ammonium concentrations than frozen precipitation, while the latter had the highest nitrate concentration. Precipitation days were classified objectively into seven groups including warm frontal, cold frontal, and convective categories. On an overall basis for six sites, there were significant differences in pH and analyte concentrations among the groups. The convective category had the highest average concentrations of hydrogen ion, sulfate, and nitrate. The cold front category was next highest in these constituents, and also had the highest ammonium concentration. In contrast, the warm front category had the lowest acidity and lowest concentrations of sulfate, nitrate, and ammonium. The average daily precipitation amount for warm fronts was approximately double that for cold fronts and convective events, so that the deposition of constituents by these phenomena was roughly the same. Individual sites varied from this general pattern, probably reflecting the particular distribution of emissions affecting that site.