Series: Park Air Profiles

Park Air Profiles - Great Smoky Mountains National Park

Autumn in Cataloochee Creek at Great Smoky Mountains NP
Visitors come to Great Smoky Mountains National Park to enjoy scenic views, including beautiful fall colors.

Air quality at Great Smoky Mountains National Park

Most visitors expect clean air and clear views in parks. Great Smoky Mountains National Park (NP) in North Carolina and Tennessee, experiences some of the highest measured air pollution of any national park in the U.S. Research and monitoring conducted in the park has shown that airborne pollutants emitted from mostly outside the Smokies are degrading park resources and visitor enjoyment. The burning of fossil fuels—coal, oil, and gas—causes most of the pollution.

Wind currents moving toward the southern Appalachians transport pollutants from urban areas, industrial sites, and power plants located both near and far. The height and physical structure of the mountains, combined with predominant weather patterns, tend to trap and concentrate human-made pollutants in and around the national park.

Air pollutants carried into the park can harm natural and scenic resources including streams, soils, forests, fish and wildlife, and visibility. The National Park Service works to address air pollution effects at Great Smoky Mountains NP, and in parks across the U.S., through science, policy and planning, and by doing our part.

Nitrogen and sulfur

Nitrogen and sulfur compounds deposited from the air may have harmful effects, including acidification, on soils, lakes, ponds, and streams. Great Smoky Mountains NP receives the highest level of acid deposition of any monitored national park. Although the Acid Rain Program has significantly reduced acid deposition throughout the East, problems remain. High ridge top ecosystems at Great Smoky Mountains NP are particularly vulnerable to acid deposition from high concentrations of nitrogen and sulfur compounds. These systems receive more deposition from rain, fog, and clouds than lower elevation areas. Additionally, low buffering capacity, short growing seasons, and shallow soils make higher elevation areas more sensitive to acid inputs. Some plants are sensitive to acidification, search for acid-sensitive plant species found at Great Smoky Mountains NP.

Excess nitrogen can also lead to nutrient enrichment, a process that changes nutrient cycling and alters plant communities. 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). High elevation soils in the park are especially sensitive to the negative effects of excess nitrogen. Nitrogen deposition exceeds the critical load for one or more park ecosystems (NPS ARD 2018).

Nitrogen and sulfur effects:
  • Acid rain with an average acidity (pH) as low as 4.6, is 3–8 times more acidic than normal rainfall (NADP 2018)
  • Acidic clouds and fog (pH 2.0) that cover high elevation forests at times, contribute to the decline of old growth red spruce forests (MADPro 2007; Cole 1992; Li & Aneja 1992; Lovett et al. 1982)
  • Acidification of forest soils, promotes loss of plant nutrients and release of toxic aluminum harmful to vegetation and stream life (Eagar & Adams 1992; Johnson et al. 1991)
  • Acidification of high elevation streams contributes to declines in aquatic diversity and native brook trout (SAMI 2002; Herlihy 1996)
  • Some high elevation park streams that drain undisturbed watersheds are the highest nitrate levels of any systems in the U.S. Nitrate levels in these streams approach the public health standard for drinking water (Stoddard 1994)
  • A number of streams in the park have been designated as "impaired" by the State of Tennessee because of acidification

Visit the NPS air quality conditions and trends website for park-specific nitrogen and sulfur deposition information. Great Smoky Mountains National Park has been monitoring atmospheric deposition of nitrogen and sulfur since 1980. Explore air monitoring »

Ground-level ozone

Milkweed is one of the ozone sensitive species found at Great Smoky Mountains NP. Milkweed is one of the ozone sensitive species found at Great Smoky Mountains NP.

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.

Ozone levels in the park have come down over the past 10 years but still sometimes exceed the National Ambient Air Quality Standard set by the U.S. Environmental Protection Agency to protect public health. Ozone is a respiratory irritant, causing coughing, sinus inflammation, chest pains, scratchy throat, lung damage, and reduced immune system functions. Children, the elderly, people with existing health problems, and active adults are most vulnerable. When ozone levels exceed, or are predicted to exceed, health standards, Great Smoky Mountain NP staff post health advisories cautioning visitors of the potential health risks associated with exposures to elevated levels.

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. Search ozone-sensitive plant species found at Great Smoky Mountains NP.

Ozone effects on vegetation:
  • Visible injury to leaves of trees and understory plants, including black cherry, tulip tree (yellow poplar), sassafras, winged-sumac, blackberry, tall milkweed and cutleaf coneflower (Neufeld et al. 1991)
  • Up to 90% of black cherry trees and milkweed plants in numerous park locations show symptoms of ozone damage
  • Decline of growth in forest trees (Somers et al. 1998; McLaughlin et al. 2007a)

Visit the NPS air quality conditions and trends website for park-specific ozone information. Great Smoky Mountains NP has been monitoring ozone since 1993. Check out the live ozone and meteorology data from Great Smoky Mountains, NP and explore air monitoring »

Visibility

Scenic view in Great Smoky Mountains NP Clean, clear air is essential to appreciating the scenic vistas at Great Smoky Mountains NP.

At Great Smoky Mountains NP, scenic views are often affected by haze that reduces how well and how far people can see. 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. Organic compounds, soot, and dust reduce visibility as well. Pollution-caused haze typically appears as a uniform whitish haze, different from the natural blue mist-like clouds for which the Smokies were named. Significant improvements in park visibility have been documented since the 1990’s. Still, visibility in the park is a long way from the Clean Air Act goal of no human caused impairment.

Visibility effects:
  • Reduction of the average natural visual range from about 110 miles (without the effects of pollution) to about 60 miles because of pollution at the park
  • Reduction of the visual range in the summer from about 80 miles to below 35 miles on high pollution days
  • Severe haze episodes can reduce visibility to 5 miles or less

Visit the NPS air quality conditions and trends website for park-specific visibility information. Great Smoky Mountains NP has been monitoring visibility since 1988. Check out the live air quality webcams at Look Rock, Purchase Knob, and Clingmans Dome; and explore air monitoring »

Particulate Matter

Concentrations of fine particles in the air at Great Smoky Mountains NP sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect human health. Fine particles (smaller than 2.5 micrometers) originate from either direct emissions by a source, such as construction sites, power plants, and fires, or reactions with gases and aerosols in the atmosphere emitted from pollution sources upwind.

Because of their small size, fine particles can get deep into the lungs and cause serious health problems. Numerous scientific studies have linked particle pollution exposure to irritation of the airways, coughing, difficulty breathing, aggravated asthma, chronic bronchitis, heart attacks, and premature death in people with heart or lung disease.

Great Smoky Mountains NP has been monitoring particulate matter since 2002. Check out the most recent particulate matter levels on our live data site and explore air monitoring »

Chappelka, A., Renfro, J., Somers, G., and Nash, B. 1997. Environmental Pollution 95: 13–18.

Chappelka, A., Skelly, J., Somers, G., Renfro, J., and Hildebrand, E. 1999. Mature Black Cherry used as a Bioindicator of Ozone Injury. Water, Air, and Soil Pollution 116: 261–266.

Cole, D.W. 1992. Nitrogen Chemistry, Deposition, and Cycling in Forests. In Atmospheric Deposition and Forest Nutrient Cycling. D.W. Johnson and S.E. Lindberg (Eds.). Springer-Verlag, New York: New York.

Copeland, S.A., Pitchford, M., and Ames, R. 2008. Regional Haze Rule Natural Level Estimates Using the Revised IMPROVE Aerosol Reconstructed Light Extinction Algorithm. Final Paper #48.

Eager, C. and Adams, M.B. 1992. Ecology and decline of red spruce in the eastern United States. Springer-Verlag, New York: New York.

[EPA] U.S. Environmental Protection Agency. 2003. Guidance for Tracking Progress Under the Regional Haze Rule. EPA-454/B-03-004. U.S. EPA Office of Air Quality Planning and Standards, Research Triangle Park, NC.

Herlihy, A., Kaufmann, P., Stoddard, J., Eshleman, K., and Bulger, A. 1996. Effects of acid deposition on aquatic resources in the Southern Appalachians with a special focus on Class I Wilderness areas. Report to the Southern Appalachian Mountains Initiative. 92 pp.

Johnson, D.W., Van Miegroet, J., Lindberg, S.E., Todd, D.E., and Harrison, R.B. 1991. Nutrient cycling in red spruce forests in Great Smoky Mountains. Canadian Journal of Forest Research 21:769–787.

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

Li, Z., and Aneja, V.P. 1992. Regional analysis of cloud chemistry at high elevations in the eastern United States. Atmospheric Environment 26A(11): 2001–2017.

Lovett, G.M., Reiners, W.A., and Olson, R.K. 1982. Cloud droplet deposition in subalpine balsam fir forest: Hydrological and chemical inputs. Science 218: 1303–1304.

[MADPro] Mountain Acid Deposition Program. 2007. Cloud deposition monitoring, Clingmans Dome, TN, Great Smoky Mountains National Park. U.S. Environmental Protection Agency, Clean Air Markets Division, Office of Air and Radiation, Washington, D.C.

McLaughlin, S.B., Nosal, M., Wullschleger, S.D., and Sun, G. 2007a. Interactive effects of ozone and climate on tree growth and water use in a southern Appalachian forest in the USA. New Phytologist 174: 109–124.

McLaughlin, S.B., Wullschleger, S.D., Sun, G., and Nosal, M. 2007b. Interactive effects of ozone and climate on water use, soil moisture content and streamflow in a southern Appalachian forest in the USA. New Phytologist 174:125–136.

Neufeld, H.S., Renfro, J.R., Hacker, W.D., and Silsbee, D. 1991. Ozone in Great Smoky Mountains National Park: Dynamics and Effects on Plants. in proc. Trophospheric Ozone and the Environment II. R. L. Berglund ed. A.W.M.A. 594–617.

[NPCA] National Parks Conservation Association. 2006. Recommendations for a Smokies Mercury Study. Letter to the State of Tennessee Department of Environment and Conservation.

[NADP] National Atmospheric Deposition Program. 2018. Annual & Seasonal Data Summary for Site TN11. Accessed May 24 2018. Available at http://nadp.slh.wisc.edu/lib/dataReports.aspx

Pardo, L. and Duarte, N. 2007. Assessment of Effects of Acidic Deposition on Forested Ecosystems in Great Smoky Mountains National Park using Critical Loads for Sulfur and Nitrogen. NPS Final Report. Available at https://irma.nps.gov/DataStore/Reference/Profile/2166643

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

[SAMI] Southern Appalachians Mountains Initiative. 2002. Final Report. 145 pp. Available at https://irma.nps.gov/DataStore/Reference/Profile/596269

Shaver, C.L., Tonnessen, K.A., and Maniero, T.G. 1994. Clearing the air at Great Smoky Mountains National Park. Ecological Applications 4: 690–701.

Somers, G.L., Chappelka, A.H., Rosseau, P., and Renfro, J.R. 1998. Empirical evidence of growth decline related to visible ozone injury. Forest Ecology and Management 104:129–137.

Stoddard, J. 1994. Long-term changes in watershed retention of nitrogen: its causes and aquatic consequences. Pgs 223–284 in Environmental chemistry of lakes and reservoirs. L. A. Baker (ed). American Chemical Society, Washington, D.C.: USA.

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., McPherson, G. T., McDonnell, T. C., Mackey, S. D., Moore, D. 2011b. 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. 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

Valente, R.J., Shea, C., Humes, K.L. and Tanner, R.L. 2007. Atmospheric mercury in the Great Smoky Mountains compared to regional and global levels. Atmospheric Environment 41:1861–1873.

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