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Air Pollution Impacts

Great Smoky Mountains National Park

Natural and scenic resources in Great Smoky Mountains National Park (NP) are susceptible to the harmful effects of air pollution. Indicators of air pollution impacts are specific natural resources, including water chemistry, aquatic biota, and vegetation, and scenic resources, such as visibility. These resources may be affected by air pollutants like ozone, sulfur, nitrogen, and fine particles. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Great Smoky Mountains NP.

  • Nitrogen & Sulfur
  • Ozone
  • Visibility

Acid Deposition and Critical Load Development

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.

A study of the park’s forest ecosystems found that the combined effects of nitrogen and sulfur deposition exceeds a threshold defined as the “critical load”; (Pardo and Duarte 2007 [pdf, 1.54 MB]). The critical load represents a threshold below which significant harmful effects to sensitive ecosystems components are not likely to occur. Critical loads were determined both for acidification and for the effects of excess fertilization from nitrogen deposition. Consequences include losses in biodiversity, the release of toxic aluminum, upset balances and nutrient cycling.

The State of Tennessee recently listed 10 park streams as impaired under the Clean Water Act because of acidification. The park is working with the State to determine how much acid deposition would need to be further reduced in order to restore and protect these streams. more »

High ridge top ecosystems at Great Smoky Mountains NP are particularly vulnerable to acid deposition that results 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.

Effects of sulfur and nitrogen deposition at Great Smoky Mountains NP include:

  • Acid rain with an average acidity (pH) as low as 4.5, is 5–10 times more acidic than normal rainfall (NADP 2000);
  • 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);
Photo of a high elevation stream at Great Smoky Mountains NP in Tennessee and North Carolina.
High elevation streams at Great Smoky Mountains NP in North Carolina and Tennessee are highly sensitive to acidification resulting from nitrogen and sulfur pollution.
  • 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).

Get Nitrogen & Sulfur Data »


Photo of healthy (top) and ozone-injured (bottom) tulip tree foliage at Great Smoky Mountains NP.
Photo of healthy (top) and ozone-injured (bottom) tulip tree foliage at Great Smoky Mountains NP.

Naturally-occurring ozone in the upper atmosphere forms a layer that absorbs harmful ultraviolet rays from the sun and protects all life on earth. However, in the lower atmosphere, ozone is an air pollutant, that forms 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. High ground-level ozone can contribute to respiratory problems in some people. Elevated ozone exposures can also harm plants, evident through visible injury to leaves or reduced growth and reproduction.

Effects of ozone on vegetation at Great Smoky Mountains NP include:

  • 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);  
  • Decline of growth in forest trees (Somers et al. 1998);
  • Reduced late-season streamflow in forested watersheds in high ozone years due to inefficient water use by trees (McLaughlin et al., 2007b).

Search the list of ozone-sensitive plant species (pdf, 184 KB) found at each national park.

Get Ozone Data »

Ozone and Public Health Concerns

Ozone concentrations at Great Smoky Mountains NP are among the highest in the East and sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health. On average, ozone levels in high elevation areas of the park can be up to twice as high as in nearby cities, including Knoxville and Atlanta. Park managers have instituted an ozone advisory program to educate employees and park visitors about the risks of exposure to unhealthy ozone levels and precautions that can be taken.

Ozone is a respiratory irritant for humans. Research shows that ozone can cause coughing, sinus inflammation, chest pains, scratchy throat, even permanent lung damage, and reduced immune system functions. Children, the elderly, people with existing health problems, and active adults are most vulnerable.

Park managers are optimistic that ozone air quality will improve at Great Smoky Mountains NP because of recent air quality regulations and other related actions.


Fine particles at Great Smoky Mountains NP and Public Health Concerns

Concentrations of fine particles in the park’s air sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health. Fine particles (smaller than 2.5 microns) originate from either direct emissions from a source, such as construction sites, power plants and fires, or are formed downwind from sources by reactions with gases and aerosols that react in the atmosphere. For example, power plants, industries and automobiles emit gases such as sulfur dioxides and nitrogen oxides, which form particles of sulfate and nitrate in the atmosphere.

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.

Many visitors come to parks to enjoy spectacular vistas. Unfortunately, these vistas are often 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 haze and reduced visibility. 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.

Visibility effects at Great Smoky Mountains NP include:

  • Reduction of the average natural visual range from about 100 miles (without the effects of pollution) to about 25 miles because of pollution at the park;
  • Reduction of the visual range in the summer from about 80 miles to below 15 miles on high pollution days;
  • Severe haze episodes can reduce visibility to 5 miles or less.

(Source: Copeland et al. 2008, [pdf, 183 KB]; EPA 2003; IMPROVE 2010)

Explore scenic vistas and live air quality data through two webcams at Great Smoky Mountains National Park.

Images of good and poor visibility at Great Smoky Mountains National Park, North Carolina and Tennessee (clear to hazy from left to right)
Air pollutants can affect visibility at Great Smoky Mountains NP, North Carolina and Tennessee (clear to hazy from left to right).

Get Visibility Data » 


Featured Content

Studies and Monitoring icon

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 Great Smoky Mountains NP.

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Last Updated: December 30, 2016