Rates of Dry Deposition Determined Using Wet/Dry Collectors

Abstract

Daily samples of dryfall were collected during the June 1982 Dry Deposition Measurement Intercomparison Study at Champaign, Illinois, using six Aerochem Metrics wet/dry collectors. Upon completion of the field experiment, these samples were analyzed at the Environmental Measurements Laboratory for pH and for their concentrations of major inorganic constituents. Contamination by rain and bird droppings rendered a number of dryfall samples unusuable. When data for these samples were removed, the remaining data displayed acceptable precision for sulfate, calcium, and magnesium. The measured deposition rates varied between 7 and 73 ng/m2/s for sulfate, between 7 and 44 for calcium, and between 0.8 and 8.1 for magnesium. The precision of the data for ammonium, nitrate, and phosphate was poor, so we have not calculated deposition rates for these constituents. The measurements of the atmospheric concentrations of sulfate reported by the Illinois State Water Survey have been used to calculate deposition velocities for particulate sulfate for 18 daily samples, even though the aerosol sampler and the dry bucket of the wet/dry collector may not sample the same size population of particulates. These velocities ranged from 0.1 to 1.2 cm/s, with a median value of 0.4 cm/s and a mean of 0.45±0.31 cm/s.