- Air quality at Great Smoky Mountains National Park
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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 »
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 »
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 »
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