Abstract
The St. Louis Metropolitan area introduces large quantities of pollutant materials into the atmosphere. These contaminants are carried large distances by prevailing winds and may affect regions considerably downwind of St. Louis. The concentrations of trace elements, sulfates, SO/sub 2/, and Freon-11 have been measured in air samples collected upwind, in, and downwind of St. Louis during July of 1973 to determine the atmospheric concentrations of these contaminants produced by St. Louis and to determine the rates at which the concentrations are decreased downwind by atmospheric mixing processes, dry deposition on the earth's surface, and, in the case of SO/sub 2/, chemical reactions. The rate of decrease in concentration due to mixing processes was determined from the rate of decrease in concentration of the essentially conservative gas Freon-11, which is released in large quantities by aerosol spray cans. The lead, bromine, and Freon-11 concentrations 60 miles downwind of the arch averaged 68%, 74% and 90%, respectively, of those at 20 miles. These numbers suggest that atmospheric mixing processes decreased the contaminant concentrations 10%, and dry deposition removed 20% between 20 miles and 60 miles downwind of St. Louis. The SO/sub 2/ concentration decreased much more rapidly with distance, and themore » concentrations 60 miles downwind averaged only 27% of the concentrations 20 miles downwind, giving a calculated atmospheric half-residence time of 3.5 hr. The surface concentrations increased somewhat with distance downwind of St. Louis due to the conversion of SO/sub 2/ to sulfate.« less
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