- Air quality at Yellowstone National Park
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Air quality at Yellowstone National Park
Most visitors expect clean air and clear views in parks. Yellowstone National Park (NP), America’s first national park and home to the Old Faithful geyser, is located in Wyoming, Montana, and Idaho. The park is downwind of significant pollutant sources, including power plants, agricultural areas, industry, and oil and gas development. Even emissions from over-snow vehicles affect winter air quality. Air pollution can harm the park’s natural and scenic resources such as surface waters, vegetation, and visibility. The National Park Service works to address air pollution effects at Yellowstone NP, and in parks across the U.S., through science, policy and planning, and by doing our part.
Highlight: Winter Air Quality
Since the mid 1970’s, snowmachine use been an increasingly popular winter tourist activity at Yellowstone NP (Yochim 1999). Although park visitation is far lower in the winter than in the summer, over-snow vehicles produce more emissions than cars (NPS 2000). Air pollution from over-snow vehicles has historically been problematic at congested locations such as park entrance stations, rest areas, thermal feature parking lots, and at Old Faithful.
In the 1990’s and early 2000’s, elevated levels of carbon monoxide (CO), fine particulate matter (< 2.5 micrometers), and hydrocarbons reached harmful levels in high traffic areas, creating a health risk for visitors and park employees. In addition, concentrations of ammonium, nitrate, sulfate, and other contaminants in snow along park roads were positively correlated with snowmobile use (Ingersoll 1999). Over-snow vehicle management changes have been effective in reducing air pollutant levels in the park. Such changes include: lowering numbers of vehicles allowed, requiring use of best available technology to reduce emissions, and modifying entrance station procedures to reduce over-snow vehicle numbers concentrated in one spot (YELL 2011).
Learn more about winter use at Yellowstone NP.
Nitrogen and sulfur
Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification, on soils, lakes, ponds, and streams. Concentrations of ammonium in precipitation (wet deposition) from regional agricultural sources are elevated and increasing at the park (NPS 2010; Ingersoll et al. 2007). High elevation ecosystems in the park are particularly sensitive to nitrogen and sulfur deposition. These systems receive more deposition than lower elevation areas because of greater amounts of snow and rain. In addition, short growing seasons and shallow soils at higher elevations limit the capacity of soils and plants to buffer or absorb sulfur and nitrogen. Lakes at elevations above 2,600 meters in the park have the greatest sensitivity to acidification due to low buffering capacity (Nanus et al. 2005, Nanus et al. 2009). Some plant species may be sensitive to acidification, search for acid-sensitive plant species found at Yellowstone NP.
Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. Vegetation communities in the park have evolved under low nitrogen conditions and are likely to be very sensitive to nutrient enrichment. Excess nitrogen may allow more weedy, invasive plants to out-compete native species, reducing biodiversity (Fenn et al. 2003). Healthy ecosystems can naturally buffer a certain amount of pollution, but as nitrogen and sulfur accumulate, a threshold is passed where the ecosystem is harmed. “Critical load” is a term used to describe the amount of pollution above which harmful changes in sensitive ecosystems occur (Porter 2005). Sensitive plant communities in the park include alpine, arid and semi-arid, grassland and meadow, and wetland (Sullivan et al. 2011a; Sullivan et al. 2011b). Arid shrublands dominated by sagebrush are widespread and are particularly vulnerable to changes caused by nitrogen deposition. Studies in other sagebrush steppe areas suggest that increased nitrogen can deplete soil moisture and affect water uptake and use by plants. This effect occurs at nitrogen loadings of about 6 kilograms per hectare per year (kg/ha/yr) (Inouye 2006). Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).
Invasive grasses are known to thrive in areas with high nitrogen deposition. These grasses out-compete native plant species, leading to native plant species decline and reduced biodiversity. Additionally, the spread of weedy grasses that burn quickly increases fire risk (Fenn et al. 2003, Allen et al. 2009; Rao et al. 2010).
Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Yellowstone has been monitoring atmospheric deposition of nitrogen and sulfur since 1980. Explore air monitoring »
Mercury and toxics
Airborne mercury, and other toxic air contaminants, when deposited are known to harm birds, salamanders, fish and other wildlife, and cause human health concerns. These substances enter the food chain and accumulate in the tissue of organisms causing reduced reproductive success, impaired growth and development, and decreased survival.
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. In addition, many natural geothermal features scattered throughout Yellowstone NP emit toxic gases and heavy metals, including mercury. Wildfires can bring mercury to the park by re-emitting formerly deposited mercury from power plants and other sources (Peterson et al. 1998, Hall et al. 2006). Over-snow vehicles also emit toxic air pollutants including benzene, toluene, and polycyclic aromatic hydrocarbons (PAHs; NPS 2000).
Yellowstone NP has been monitoring mercury since 2004. Explore air monitoring »
At ground level, ozone is harmful to human health and the environment. Ground-level ozone does not come directly from smokestacks or vehicles, but instead is formed when other pollutants, mainly nitrogen oxides and volatile organic compounds, react in the presence of sunlight.
Over the course of a growing season, ozone can damage plant tissues making it harder for plants to produce and store food. It also weakens plants making them less resistant to disease and insect infestations. Some plants are more sensitive to ozone than others. There are a few ozone-sensitive plants in Yellowstone NP including Populus tremuloides (quaking aspen), Apocynum androsaemifolium (bitterroot), and Salix exigua (Desert willow). A risk assessment concluded that plants in at Yellowstone NP are at low risk for ozone damage (Kohut 2007; Kohut 2004). Search ozone-sensitive plant species found at Yellowstone NP.
Visit the NPS air quality conditions and trends website for park-specific ozone information. Yellowstone NP has been monitoring ozone since 1996. Check out the live ozone and meteorology data from Yellowstone NP and explore air monitoring »
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, these scenic vistas are sometimes obscured by haze. Visibility reducing haze is caused by tiny particles in the air, and these particles can also affect human health. 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 contribute to particulate matter and impair visibility. Winter inversion layers trap local emissions in and near the park. Significant improvements in park visibility on clearest days have been documented since the 1990’s. There is no significant trend for visibility on haziest days in the park, likely due to the influence of wildfires on these days. Overall, visibility in the park still needs improvement to reach the Clean Air Act goal of no human caused impairment.Visibility effects:
- Reduction of the average natural visual range from about 180 miles (without the effects of pollution) to about 140 miles because of pollution at the park
- Reduction of the visual range to below 75 miles on high pollution days
Visit the NPS air quality conditions and trends website for park-specific visibility information. Yellowstone NP has been monitoring visibility since 1999. Check out the live air quality webcam and explore air monitoring »
Fenn, M. E., Haeuber, G. S., Tonnesen, J. S., Baron, J. S., Grossman-Clarke, S., Hope, D., Jaffe, D. A., Copeland, S., Geiser, L., Rueth, H. M., and Sickman, J. O. 2003. Nitrogen emissions, deposition and monitoring in the western United States. Bioscience 53: 391–403.
Hall, B. D., Olson, M. L., Rutter, A. P., Frontiera, R. R., Krabbenhoft, D. P., Gross, D. S., Yuen, M., Rudolph, T. M., Schauer, J. J. 2006. Atmospheric mercury speciation in Yellowstone National Park. Science of the Total Environment 367 (1): 354–366.
Ingersoll, G. P., Mast, M. A., Nanus, L., Handran, H. H., Manthorne, D. J., and Hultstrand, D. M. 2007. Rocky Mountain snowpack chemistry at selected sites, 2004: U.S. Geological Survey Open-File Report 2007—1045, 15 p. Available at http://pubs.usgs.gov/of/2007/1045/
Ingersoll, G. P. 1999. Effects of Snowmobile Use on Snowpack Chemistry in Yellowstone National Park, 1998. U.S. Geological Survey Water Resources Investigation Report 99–4148, 23 pp. Available at https://pubs.er.usgs.gov/publication/wri994148
Inouye, R. S. 2006. Effects of shrub removal and nitrogen addition on soil moisture in sagebrush steppe. Arid Environments 65: 604–618.
Kohut R.J. 2007. Ozone Risk Assessment for Vital Signs Monitoring Networks, Appalachian National Scenic Trail, and Natchez Trace National Scenic Trail. NPS/NRPC/ARD/NRTR—2007/001. National Park Service. Fort Collins, Colorado. Available at https://www.nps.gov/articles/ozone-risk-assessment.htm
Kohut RJ. 2007. Reassessment of Yellowstone National Park Ozone Risk. NPS/NRPC/ARD/NRTR—2007/001. National Park Service. Fort Collins, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2250221
Kohut, R. 2004. Assessing the Risk of Foliar Injury from Ozone on Vegetation in Parks in the Greater Yellowstone Network. Available at https://irma.nps.gov/DataStore/Reference/Profile/2181291
Krabbenhoft, D. P., Olson, M. L., Dewild, J. F., Clow, D. W., Striegl, R. G., Dornblaser, M. M., and VanMetre, P. 2002. Mercury loading and methylmercury production and cycling in high-altitude lakes from the western United States. Water, Air, and Soil Pollution, Focus 2: 233–249.
Nanus, L., Williams, M. W., Campbell, D. H., Tonnessen, K. A., Blett, T., and Clow, D. W. 2009. Assessment of lake sensitivity to acidic deposition in national parks of the Rocky Mountains. Ecological Applications 19(4): 961–973.
Nanus, L., Campbell, D. H., Williams, M. W. 2005. Sensitivity of Alpine and Subalpine Lakes to Acidification from Atmospheric Deposition in Grand Teton National Park and Yellowstone National Park, Wyoming. US Department of the Interior, US Geological Survey, Reston, VA. Scientific Investigations Report 2005—5023. Available at https://pubs.er.usgs.gov/publication/sir20055023
[NPS] National Park Service. 2010. Air Quality in National Parks: 2009 Annual Performance and Progress Report. Natural Resource Report NPS/NRPC/ARD/NRR—2010/266. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2166247
[NPS] National Park Service. 2000. Air Quality Concerns Related to Snowmobile Usage in National Parks. National Park Service, Air Resources Division, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/602835
Peterson, D. L., Sullivan, T. J., Eilers, J. M., Brace, S., Horner, D., Savig, K., and Morse, D. 1998. Assessment of air quality and air pollutant impacts in national parks of the Rocky Mountains and northern Great Plains. Report NPS/CCSOUW/NRTR—98/19. National Park Service, Air Resources Division, Denver, CO. Chapter 4: Grand Teton National Park. Available at https://irma.nps.gov/DataStore/Reference/Profile/11733 (pdf, 694 KB).
Porter, E. and Johnson, S. 2007. Translating science into policy: Using ecosystem thresholds to protect resources in Rocky Mountain National Park. Environmental Pollution 149: 268–280.
Porter, E., Blett, T., Potter, D.U., Huber, C. 2005. Protecting resources on federal lands: Implications of critical loads for atmospheric deposition of nitrogen and sulfur. BioScience 55(7): 603–612. https://doi.org/10.1641/0006-3568(2005)055[0603:PROFLI]2.0.CO;2
Saros, J. E., Clow, D. W., Blett, T., Wolfe, A. P. 2010. Critical nitrogen deposition loads in high-elevation lakes of the western U.S. inferred from paleolimnological records. Water, Air, and Soil Pollution 216 (1–4): 193–202.
Sullivan, T. J., McDonnell, T. C., McPherson, G. T., Mackey, S. D., Moore, D. 2011a. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/nitrogen-risk-assessment.htm
Sullivan, T. J., T. C. McDonnell, G. T. McPherson, S. D. Mackey, and D. Moore. 2011b. Evaluation of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from atmospheric nitrogen deposition: Greater Yellowstone Network (GRYN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/308. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2168632
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011c. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado. Available at https://www.nps.gov/articles/acidification-risk-assessment.htm
Sullivan, T. J., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011d. Evaluation of the sensitivity of inventory and monitoring national parks to acidification effects from atmospheric sulfur and nitrogen deposition: Greater Yellowstone Network (GRYN). Natural Resource Report NPS/NRPC/ARD/NRR—2011/360. National Park Service, Denver, Colorado. Available at https://irma.nps.gov/DataStore/Reference/Profile/2170584
Sullivan T.J. 2016. Air quality related values (AQRVs) in national parks: Effects from ozone; visibility reducing particles; and atmospheric deposition of acids, nutrients and toxics. Natural Resource Report. NPS/NRSS/ARD/NRR—2016/1196. National Park Service. Fort Collins, Colorado. Available at https://www.nps.gov/articles/aqrv-assessment.htm
[YELL] Yellowstone National Park. 2011. Scientific Assessment of Yellowstone National Park Winter Use, Draft Report. National Park Service, Yellowstone Center for Resources, Yellowstone National Park, Wyo., YCR—2011-xx.
Yochim, M. J. 2009. The Development of Snowmobile Policy in Yellowstone National Park. Yellowstone Science 7(2): 2–10.