Zion National Park Air Quality Information
In 1977 Zion NP was designated a Class I air quality area, receiving the highest protection under the Clean Air Act. Pinyon pine/juniper is the dominant vegetative community, with other areas of shrubland and ponderosa pine. The Virgin River cuts through the park, and numerous springs, seeps, streams, and ponds are important aquatic resources.
Both local and distant air pollutant sources affect air quality in Zion NP. Nearby large point sources include power plants, refineries, and lime kilns in Coconino County, Arizona, and Clark County, Nevada. Pollutants also travel greater distances to the park from both mobile and point sources throughout the Southwest.
The air quality related values (AQRVs) of Zion NP are those resources that are potentially sensitive to air pollution, and include vegetation, wildlife, water quality, soils, visibility and night skies. At present, visibility has been identified as the most sensitive AQRV in the park; other AQRVs may also be very sensitive, but have not been sufficiently studied. Although visibility in the park is still superior to that in many parts of the country, visibility in the park is often impaired by light-scattering pollutants (haze).
As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, visual air quality in Zion NP has been monitored using an aerosol sampler (2000-present), and a 35mm camera (1985-1991). The U.S. Environmental Protection Agency’s Regional Haze regulations require States to establish goals for each Class I air quality area to improve visibility on the haziest days and ensure no degradation occurs on the clearest days. The data record at Zion NP (from the aerosol sampler) is insufficient to analyze temporal trends. However, an analysis of 1990-1999 data from the Colorado Plateau region indicates that visibility in other parks is improving somewhat on the clearest days, but degrading on the haziest days.
Surface waters in Zion NP are expected to be generally well-buffered and, therefore, not likely to be acidified by atmospheric deposition. Most soils are also likely to be well-buffered from acidification. However, there may be areas in the park where rock is resistant to weathering and soils and water (e.g., in small ponds and potholes) may be sensitive to inputs of acidic deposition.
Soils and vegetation in the park may also be sensitive to nutrient enrichment from nitrogen deposition. In some parts of the country, nitrogen deposition has altered soil nutrient cycling and vegetation species composition; native plants that have evolved under nitrogen-poor conditions have been replaced by invasive species better able to utilize nitrogen. Studies are underway in Canyonlands NP to investigate nitrogen effects on soil dynamics, exotic plant invasiveness, and biological soil crusts.
Deposition of pollutants, including sulfur and nitrogen, is not measured in Zion NP. However, information from deposition measurements at Bryce Canyon NP and Canyonlands NP can be used to estimate deposition at Zion NP. Wet deposition has been monitored in Bryce Canyon NP (1985-present) as part of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The site ID is UT99. Dry deposition rates have been estimated for Canyonlands NP (site CAN407), 1995-present, as part of the Clean Air Status and Trends Networks (CASTNet). Rates of atmospheric deposition of nitrogen and sulfur are relatively low in these parks, but elevated above natural conditions. Trend analysis by NADP shows that annual wet nitrogen deposition has increased from 1985-present in Bryce Canyon NP; sulfur deposition has slightly decreased. A CASTNet analysis of site data for 1995-2001 indicates that annual dry deposition of nitrogen has remained steady in Canyonlands NP; dry deposition of sulfur has decreased slightly. Other parks on the Colorado Plateau show similar trends, with nitrogen deposition increasing or staying the same, and sulfur deposition decreasing.
Several plant species that occur in Zion NP are known to be sensitive to ozone, including Populus tremuloides (quaking aspen), Symphoricarpos oreophilus (snowberry), and Pinus ponderosa (ponderosa pine). An ozone monitor was recently (2003) installed in the park. Information from monitoring in other parks on the Colorado Plateau indicate that ozone concentrations and cumulative annual ozone doses fall within a range that may produce visible effects or growth effects on sensitive plant species. In addition, data from 1990-1999 indicate that ozone is increasing throughout the Southwest. In 1999, the National Park Service Air Resources Division surveyed vegetation in Zion NP and found probable ozone injury on several species, including Symphoricarpos oreophilus (snowberry). Surveys in nearby Cedar Breaks NM and Bryce Canyon NP also found symptoms of ozone injury on vegetation.
Additional information on in-park emissions at Zion NP is available in 2000 Air Emission Inventory-Zion National Park (January 2003). Disclaimer: Links within the above document were valid as of the date published.
Additional information relative to air quality and air quality related values at Zion NP is available in D. Binkley et al. 1997. Status of Air Quality and Related Values in Class I National Parks and Monuments of the Colorado Plateau. National Park Service. Denver, CO.