Air Quality in the National Park System

Air Quality in the National Park System
		by *Bruce L. Nash* National Biological Service-AIR *Kathy Tonnessen* National Biological Service *David Joseph* *Miguel Flores* National Park Service
The National Park Service (NPS) Organic Act and the federal Clean Air Act require the NPS to protect the natural resources of the lands it manages from the adverse effects of air pollution. The NPS established a program to measure ozone--the air pollutant that is most widespread and injurious to human health and vegetation--at more than 40 monitoring sites within the National Park System.

NPS sites in southern and central California, the Great Lakes region, and the northeast and east-central United States generally record the highest ozone concentrations in the NPS network. Ozone levels exhibit strong seasonal and diurnal temporal trends, and year-to-year variation may be significant (Figure).

Figure. Highest daily 1-h ozone concentration per month.

The 1987-91 NPS trend in maximum ozone concentrations closely resembles the corresponding trend for the entire nation. The National Biological Service (NBS) National Air Quality Research Program sponsors surveys to document ozone injury to vegetation. Current monitoring concentrates on sensitive indicator plants, including hardwoods and some herbaceous plants in the eastern United States and conifers in the West. Controlled fumigation studies have confirmed that elevated ambient ozone levels can cause decreased growth rate, decreased biomass, and premature defoliation in sensitive species such as black cherry (Prunus serotina), American sycamore (Platanus occidentalis), yellow-poplar (Liriodendron tulipifera), and ponderosa pine (Pinus ponderosa).
Acid deposition is a regional pollutant monitored at 30 NPS units as part of the National Atmospheric Deposition Program (NADP). Ten years of wet deposition (e.g., pollutants that may come down in rain or snow) data permit researchers to estimate loading of nitrate, sulfate, and hydrogen ions to sensitive ecosystems. NADP data show that the NPS units with the greatest acid loading are in the eastern United States, with Acadia, Cape Cod, Shenandoah, and Great Smoky Mountains national parks showing annual average wet deposition pH values of 4.4-4.6. These values do not reflect the contributions of cloudwater, fogwater, and dry deposition (e.g., particles and gases) to the total loading of acids, nitrogen, and sulfate to ecosystems that are sensitive to acidic inputs. NADP samplers do not measure snow efficiently and do not account for the effect of snowmelt pulses on sensitive alpine lakes and streams in the spring at high-elevation sites in the Sierra Nevada, the Cascades, and the Rocky Mountains. Research at Shenandoah National Park has shown that deposition-driven episodes in streams can result in pH levels low enough to affect native fish species.
Any assessment of ecosystem health must consider the composition of the atmosphere and its interactions with the biological and physical components of the ecosystem under investigation. Although we have some understanding of the biological effects of air pollution, more studies are necessary to ensure the protection of our natural resources.
		For further information: Bruce L. Nash National Biological Service-AIR National Air Quality Research Program PO Box 25287 Denver, CO 80225