SOURCE APPORTIONMENT OF RAIN WATER IMPURITIES IN CENTRAL ILLINOIS

Abstract

The identity and relative contributions of various sources of impurities in precipitation are needed to understand the acidic precipitation phenomenon. This paper reports results of using factor analysis and a chemical element balance (CEB) to apportion sources of impurities in a series of 191 wet-only event precipitation samples collected near Champaign, IL. Factor analysis showed that four major groups of constituents accounted for 86% of the variance in the data: crustal dust, pollutants with gaseous precursors, sea salt, and possibly strong acids. Apportionment of plausible sources by CEB yielded estimates of a 2% contribution of sea salt to the total mass of impurities, a 32% contribution by ammonium and sulfates (including sulfuric acid) and a 16% contribution from nitrates. Calculated results were more sensitive to spatial variations in crustal source composition than to differences in composition between bulk materials and ‘source aerosols.’ Without taking account of insoluble materials, the probable contributions of soil dust and road dust were 7 and 12%, respectively, with outside limits of 3–8% and 8–24%, respectively. A reasonable assumption regarding Ca and K solubility increased the likely soil contribution from 7 to 15%, but had little effect on the road dust contribution. The use of extracted source material compositions as input to the CEB analyses to compensate for analysis of only the soluble portion of the precipitation samples was not successful.