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ATMOSPHERIC DEPOSITION OF TOXIC METALS TO LAKE MICHIGAN: PRELIMINARY ANNUAL MODEL CALCULATIONS
Citation:
Clark, T. ATMOSPHERIC DEPOSITION OF TOXIC METALS TO LAKE MICHIGAN: PRELIMINARY ANNUAL MODEL CALCULATIONS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-92/239.
Description:
Concern is growing for the environmental water quality of the Great Lakes. tmospheric deposition of toxic substances is recognized as a major pathway of contaminants to the water medium. o estimate the annual atmospheric loadings of five toxic metals -- arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) -- to Lake Michigan, the Regional Lagrangian Model of Air Pollution (RELMAP) was applied using a preliminary 1985 airborne toxics emissions inventory developed by EPA for U.S. and Canadian anthropogenic sources. t 3-h intervals this model creates pollutant puffs containing particles with diameters of either 0.5 um or 5.0 um, transports them across the eastern North American domain, and calculates wet and dry deposition amounts for each unit-degree cell. otal direct deposition amounts to the lake are determined from these calculated amounts and a land-use inventory that defines the water surface portion of each cell. he preliminary model results indicate that Pb deposition, approaching 700,000 kg/yr, exceeds by an order of magnitude the deposition of the other metals, which range from 18,000 kg/yr to 58,000 kg/yr. he relative contribution of dry and wet depositions to the total depositions is highly dependent on the particle size. or the smaller particles dry deposition accounted for 10% or less of the total deposition versus the nearly 40% for the larger particles. owever, the total deposition to the lake is not nearly as sensitive to particle size.