| The prospect of a new industrial development in northeastern Minnesota to recover copper and nickel metal raises the potential for major atmospheric impacts in this pristine wilderness region.;The regional nature of the problem required an assessment tool that could predict mesoscale atmospheric impacts. In response to this need, a new mesoscale atmospheric diffusion model was developed. This model, the modified gaussian model, incorporates the processes of dry deposition, wet scavenging, and oxidation of sulfur dioxide gas to sulfate. Horizontal dispersion is approximated by the gaussian distribution, and vertical dispersion is assumed to be uniform from the ground to the mixing height. The model handles 25 sources, 50 receptors, 5 meteorological stations, and 25 pollutants.;The model was verified using deposition and ambient air data collected around Sudbury, Ontario, and it was also compared to two other diffusion models. Generally, the predicted results were within a factor of two accuracy at the 95% confidence interval. The model is not as accurate for single 24-hour events as for monthly or annual averages. A sensitivity analysis was also performed on the primary input parameters.;The existing air quality in the region is typical of mid-continental rural areas; elevated 24-hour particulate concentrations were measured near population centers and mining areas.;The purpose of this research project was to characterize northeastern Minnesota in terms of the ambient air concentrations and deposition patterns of selected pollutants (sulfur dioxide, sulfate, total particulate, copper, nickel, arsenic, cadmium, lead, and mercury) for a base year, 1977, and a projected year, 1985. These data were then used to assess the potential ambient air impacts of copper-nickel smelting in terms of the health, environmental, and regulatory issues.;A tabulation of major point sources within 150 kilometers of the ore body showed that emissions due to existing and projected sources are expected to increase by 130% for sulfur dioxide and decrease by 35% for particulates by 1985.;Local point sources were found to account for the existing sulfur dioxide levels, 15% of total sulfate deposition, and less than 1% of particulate levels. Particulate concentrations are dominated by area sources (roads and tailings basins); transport from outside the region appears to be an important source of sulfates.;Without copper-nickel development, there does not appear to be a problem, now or in the future, which would threaten to exceed the ambient air quality standards for sulfur dioxide. Elevated particulate levels exceeding the secondary standards are predicted as a result of regional point source growth.;The modeling of three hypothetical smelter configurations along with the regional sources indicates that the possibility of smelter siting in the region will be most seriously affected by the short-term prevention of significant deterioration restrictions due to the proximity of the Class I areas.;In terms of human health and vegetation impacts, the projected release of sulfur dioxide, sulfates, and total particulates from the smelter models is not expected to have significant consequences. Over the long-term, the concentration and deposition rates of metals may pose a problem within 10 kilometers of the smelter.;The ambient concentrations and deposition rates of copper, nickel, and sulfate from a smelter are predicted to be the same order of magnitude or higher than existing levels; the contributions of arsenic, cadmium, lead, and mercury are predicted to be two orders of magnitude below current levels.;The accumulation of copper, nickel, and sulfate from a smelter could be important in determining the productive life span of the region's low alkalinity lakes over the long-term and during a few days each year when the spring melt occurs. |
