Grand Canyon National Park Air Quality Information
Overview
Both local and distant air pollutant sources affect air quality in Grand Canyon NP. Large power plants in Coconino and Navajo counties in Arizona and Clark County in Nevada are the largest nearby point sources of both sulfur dioxide and nitrogen oxides. Pollutants also travel great distances to the park from industrial and urban areas of southern California, southern Arizona, southern Nevada, and northern Mexico. Vehicles in the park and prescribed fires are local sources of air pollutants, but do not add appreciably to the total emissions of Coconino County. Nearby forest fires, both wild and managed, have the potential for serious visibility impacts to the park.
The air quality related values (AQRVs) of Grand Canyon NP are those resources that are potentially sensitive to air pollution, and include vegetation, wildlife, water quality, soils, and visibility. At present, visibility has been identified as the most sensitive AQRV in the park. Although visibility in the park is still superior to that in many parts of the country, visibility in the park is usually impaired by light-scattering pollutants (haze). Visibility averages 106 miles and can exceed 160 miles on the clearest days; haze can reduce visibility to less than 50 miles. Studies (e.g., WHITEX, Project MOHAVE) have identified point sources in Nevada and Arizona that contribute to visibility impairment in the park, but these studies also found that distant area sources (e.g., Southern California) are also large contributors to haze in the park.
As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, visual air quality in Grand Canyon NP has been monitored using an aerosol sampler (1987 through the present), transmissometer (1987 through the present), nephelometer (1997-present), and 35mm camera (1978 to present). The U.S. Environmental Protection Agency’s new 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. An analysis of 1990-1999 data indicates that visibility in Grand Canyon NP is degrading on the worst visibility days and staying about the same on the clearest days.
Surface water chemistry data for Grand Canyon NP indicate that park surface waters are well buffered and, therefore, not likely to be acidified by atmospheric deposition. Soils are also likely to be well-buffered from acidification. There is no information available on the effects (e.g., fertilization) of nitrogen deposition on waters or soils in the park. In some parts of the country, nitrogen deposition has caused changes in soil nutrient cycling and vegetation species composition.
Wet deposition has been monitored in Grand Canyon NP since 1981 as part of the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The site ID is AZ03. Rates of atmospheric deposition of nitrogen and sulfur in rain are relatively low in Grand Canyon. An NADP analysis of site data from 1990-1999 indicates that wet sulfate deposition rates decreased slightly during that period; total inorganic nitrogen (nitrate and ammonium) wet deposition increased slightly during that period.
Dry deposition has been estimated for Grand Canyon NP (site GRC474) since 1989 as part of the National Dry Deposition Network (NDDN) and the Clean Air Status and Trends Networks (CASTNet). Data indicate that, for the period 1997-2000, dry deposition contributed about 45 percent of total inorganic nitrogen deposition and about 28 percent of total sulfur deposition. A CASTNet analysis of site data for 1990-2000 indicates that dry deposition rates of both nitrogen and sulfur have stayed about the same during that period.
Several plant species that occur in Grand Canyon are known to be sensitive to ozone (e.g., Populus tremuloides) although the specific genotypes found in the park have not been tested under controlled conditions for sensitivity. Tropospheric (ground-level) ozone concentrations have been monitored in Grand Canyon NP in 1981, 1983, and 1989-present. An analysis of 1990-1999 data indicates that ozone concentrations significantly increased in the park during that period. The observed concentrations fall within a range that may produce visible effects or growth effects on very sensitive plant species. No signs of injury from air pollution have been reported for vegetation in Grand Canyon NP; however, widespread, systematic surveys for ozone injury have not been conducted. Sulfur dioxide concentrations have been monitored from 1988-present. Measured values are far below thresholds of suggested sensitivity for any plants.
Increased exposure to ultraviolet (UV) radiation has negative implications for human health and plant productivity. Human activities have resulted in a decline in stratospheric (upper atmosphere) ozone levels which, in turn, may cause increases in UV exposure. UV-B radiation has been monitored in the Park since 1996 as part of the Department of Agriculture’s UV-B Monitoring Program.
Since 1999, dioxins and furans have been sampled in the park four times a year as part of the EPA’s National Dioxin Air Monitoring Network. The concentrations of dioxins and furans in the park have consistently been among the lowest measured by the network.
Additional information on in-park emissions at Grand Canyon NP is available in 2000 Air Emissions Inventory- Grand Canyon National Park (September 2002).
Additional information relative to air quality and air quality related values at Grand Canyon 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.