Richard G. Semonin Principal Investigator TABLE OF CONTENTS THE REMOVAL OF ATMOSPHERIC SO2 BY DRY DEPOSITED ROAD DUST

We present the first analysis of precipitation chemistry data from the Great LakesAtmospheric Deposition (GLAD) network of wet-only precipitation samplers. Lake loadings werecalculated from 1or 2-yr (1982-1983) volume-weighted mean ion concentrations and 30-yr meanannual precipitation amounts, using an objective analysis method to interpolate measurements to a40 x 40 km square grid over the Great Lakes region. The results show that atmospheric loadings ofCd, Pb, and other cations to the Great Lakes are in many cases considerably smaller than thoseestimated from the bulk precipitation measurements of the early 1970s. For Pb, some portion of thedifferences can be accounted for by the decrease in emissions that resulted from reductions in the Pbcontent of gasoline. Valid dry deposition in the bulk samplers also accounts for a portion of thedifferences. However, for the most extreme differences, contamination of the bulk collectors byresuspended local surface dust is likely to be a major cause. Good agreement was noted between theprecipitation-only loadings derived from the GLAD data and those recently given by Strachan andEisenreich (1987).ADDITIONAL INDEX WORDS: Trace metals, atmospheric deposition, pollution load, toxicsubstances.