Air Pollution Threats to US National Parks of the Great Lakes Region

The Great Lakes region of the interior of North America supports a large human population, a major industrial base, and recreational and scenic amenities of unusual contrast and quality. To protect portions of this landscape and meet national recreational needs, the US Federal Government has established 10 National Parks, Monuments, and Lakeshores, in the region, extending from northern Minnesota to the southern shore of Lake Erie. However, air pollutant sources from the industrial Midwest, and large-scale coal combustion for electricity along the Ohio Valley, show evidence of significantly threatening the resource qualities protected in these parks. A review of the natural resources and amenities in each of the National Parks, Monuments, and Lakeshores, in the region shows that scenic vistas are of primary significance, with unique biota (largely northern coniferous species and associated bird-life) and clear water also prominent. Pollutant concentrations in the southern sites, however, are above the thresholds that are known to produce stress, foliage damage, and altered growth-rates on many sensitive species, including the coniferous trees. These pollutants include gases such as sulphur dioxide and nitrogen oxides (NOX) that are primary emissions of relatively local origin, as well as pollutants such as sulphate particulates, ozone, and acidic deposition, produced by chemical transformations during long-distance atmospheric transport. The particulates, in combination with the high average summer humidity, produce a reduction of visibility at the southern sites, and hence the partial loss of an important amenity.