For more information about National Park Service air resources, please visit http://www.nature.nps.gov/air/.
Air Pollution Impacts
Yellowstone National Park
Natural and scenic resources in Yellowstone National Park (NP) are susceptible to the harmful effects of air pollution. Nitrogen, sulfur, mercury, ozone, and fine particles impact natural resources such as surface waters and vegetation, and scenic resources such as visibility. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Yellowstone NP.
- Nitrogen & Sulfur
- Toxics & Mercury
How much nitrogen is too much?
Nitrogen is a fertilizer and some nitrogen is necessary for plants to grow. However, in natural ecosystems, too much nitrogen disrupts the balance of communities, allowing weedier vegetative and aquatic plant species to thrive. A recent spatial analysis identified certain high elevation lakes and sensitive vegetation communities at Yellowstone NP that are at risk from atmospheric deposition of nitrogen (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 12 MB]). Sensitive plant communities include arid and semi-arid areas which, in Yellowstone NP, are dominated by sagebrush. Studies in other sagebrush steppe areas suggest that increased nitrogen can deplete soil moisture and affect water uptake and transpiration by plants. This effect occurs at nitrogen loadings of about 6 kilograms per hectare per year (kg/ha/yr) (Inouye 2006). This loading is termed the “critical load,” and defines the level at which nitrogen may cause harmful changes to the ecosystem (Porter and Johnson 2007). Critical loads for aquatic and terrestrial resources can be used to establish goals for ecosystem recovery.
Nitrogen and sulfur compounds deposited from air pollution can harm surface waters, soils, and vegetation. High elevation ecosystems in the park are also particularly sensitive to nitrogen and sulfur deposition. Not only do these systems receive more deposition than lower elevation areas because of greater amounts of snow and rain, but short growing seasons and shallow soils limit the capacity of soils and plants to buffer or absorb sulfur and nitrogen. Lakes located at elevations greater than about 2,600 meters in the park have the greatest sensitivity to acidification from atmospheric deposition due to low buffering capacity (Nanus et al. 2005 [pdf, 4.0 MB], Nanus et al. 2009). Excess nitrogen loading can also contribute to overenrichment, causing changes to sensitive aquatic and terrestrial plant communities. Sensitive vegetation communities in the park include alpine, arid and semi-arid, grassland and meadow, and wetland (Sullivan et al. 2011a; Sullivan et al. 2011b [pdf, 12 MB]). Arid shrublands make up a significant portion of vegetative communities in the park and are particularly vulnerable to changes caused by nitrogen deposition. Nitrogen loading may disrupt soil nutrient cycling and alter plant communities. Invasive grasses thrive in areas with high nitrogen deposition, displacing native vegetation adapted to low N conditions. The fire risk subsequently increases due to extensive areas of weedy grasses (Fenn et al. 2003).
Effects of nitrogen and sulfur deposition at Yellowstone NP include:
- Concentrations of ammonium in wet deposition from regional agricultural sources are elevated and increasing at the park (NPS 2010 [pdf, 2.8 MB]; Ingersoll et al. 2007);
- Concentrations of ammonium, nitrate, sulfate, and other contaminants in snow along park roads are positively correlated with snowmobile use (Ingersoll 1999 [pdf, 660 KB]). more on Winter Use »
Toxics, including heavy metals like mercury, accumulate in the tissue of organisms. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, and decreased survival. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals such as flame retardants for fabrics, some of which are known or suspected to cause cancer or other serious health effects in humans and wildlife.
Mercury has been detected in air, snowpack, and lake water samples from Yellowstone NP (Hall et al. 2006; Ingersoll et al. 2007; Krabbenhoft et al. 2002). Regional coal-burning power plants contribute to airborne mercury deposited in the park, however many natural geothermal features scattered throughout Yellowstone NP also emit toxic gases and heavy metals, including mercury (Peterson et al. 1998 [pdf, 905 KB]). Nearby wildfires also contribute mercury to the park by re-emitting formerly deposited mercury from powerplants and other sources (Hall et al. 2006).
Naturally-occurring ozone in the upper atmosphere absorbs the sun’s harmful ultraviolet rays and helps to protect all life on earth. However, in the lower atmosphere, ozone is an air pollutant, forming when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds from gasoline, solvents, and vegetation in the presence of sunlight. In addition to causing respiratory problems in people, ozone can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth, and reproduction.
There are a few ozone-sensitive plants in Yellowstone NP including Populus tremuloides (quaking aspen), Rhus trilobata (skunkbush), and Salix scouleriana (Scouler’s willow). The low levels of ozone exposure at Yellowstone NP make the risk of foliar ozone injury to plants low (Kohut 2004 [pdf, 120 KB]).
Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park.
Visitors come to Yellowstone NP to enjoy views of spectacular geysers, waterfalls, canyons, and wildlife in densities rarely observed in other areas of North America. Unfortunately, such park scenic vistas are sometimes obscured by haze caused by fine particles in the air. Many of the same pollutants that ultimately fall out as nitrogen and sulfur deposition contribute to this haze and visibility impairment. Additionally, organic compounds, soot, and dust reduce visibility. Smoke from nearby forest fires, and oil and gas development in the region, also contribute to particulate matter and impair visibility. Winter inversion layers exacerbate the effects of snow machine emissions in and near the park. more on Winter Use »
Visibility effects at Yellowstone NP include:
- Reduced visibility sometimes due to human-caused haze and fine particles of air pollution;
- Reduction of the average natural visual range from about 180 miles (without the effects of pollution) to about 120 miles because of pollution at the park;
- Reduction of the visual range to below 70 miles on high pollution days.
(Source: IMPROVE 2010)
Explore scenic vistas through live webcams at Yellowstone National Park.
Studies and monitoring help the NPS understand the environmental impacts of air pollution. Access air quality data and see what is happening with Studies and Monitoring at Yellowstone NP.
Last Updated: August 08, 2011