Because air quality “increments” were exceeded in North Dakota in the early 1980s, the NPS was required under the Clean Air Act to make a determination as to whether or not the exceedance would be likely to produce an “adverse impact” to air quality-related values in the Theodore Roosevelt National Park. Lichen species determined to be present in the park (Wetmore 1983) and potentially sensitive to air pollutants were evaluated with regard to concentrations of air pollutants known to cause health impacts to these species. The analysis determined that the current and predicted concentrations of sulfur dioxide at.
