Shenandoah National Park (SHEN) has among the most comprehensive air quality monitoring and research program of all national parks and wilderness areas that are afforded special protection under the Clean Air Act. The park’s monitoring and research program focuses on visibility, acidic deposition, gaseous pollutants, and the acid-base status of streams. By the late 1990s, park managers had determined the need for a comprehensive, state-of-the-science assessment of SHEN’s air quality and related values for use as a tool in the air policy, planning, permit review, scientific, and outreach arenas. This assessment by E&S and collaborating university and federal agency scientists addresses that need by evaluating the current and possible future status of air quality and air pollution effects in SHEN. It focuses on the park’s key known air quality related values (AQRVs), including visibility, streamwater chemistry, fish, soils, and vegetation, and the human-caused air pollutants that most affect them.
An enhanced version of the RADM (Regional Acid Deposition Model) was used to project future air quality and deposition. Four scenarios of future emissions were developed for the report, based on existing emissions regulations, and more aggressive controls on utilities and on industrial point sources and mobile sources. Under the set of rules that existed or were being promulgated at the time of the study, sulfur dioxide emissions within the SHEN airshed will be reduced by an estimated 47% from 1990 levels and nitrogen oxide emissions reduced by 41%. Two of the scenarios represented significant additional reductions beyond current plans.
Dose-response calculations and simulation modeling were used to evaluate possible future changes in the extent of damage to visibility, aquatic, and forest resources in SHEN in response to ambient air quality, acidic deposition, and ozone exposure, respectively. Alternative deposition and air quality scenarios were specified for aquatic and visibility projections from the RADM model estimates of future conditions. Ozone exposure scenarios were based on measured 5-month SUM06 exposures for the period 1997 to 1999, and a suite of future exposure scenarios, ranging from about an 80% decrease to a three-fold increase in the ambient 5-month (12 hr) SUM06 ozone exposure. The modeling was conducted using the Model of Acidification of Groundwater in Catchments (MAGIC) model for aquatic effects, the TREGRO model for growth of individual tree species, and the ZELIG model for forest stand composition and growth. Future visibility conditions were projected for each of the deposition scenarios on the basis of expected reductions in fine particle concentrations in the atmosphere and the known contribution of each particle type to light extinction.