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Air Pollution Impacts

Shenandoah National Park

Natural and scenic resources in Shenandoah 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 sulfur, nitrogen, ozone, and fine particles. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Shenandoah NP.

  • Sulfur & Nitrogen
  • Ozone
  • Visibility

Acid Deposition and Critical Load Development

Shenandoah NP receives among the highest measured deposition of both sulfur and nitrogen of all monitored national parks. Although the Acid Rain Program has significantly reduced acid deposition throughout the East, problems remain. Consequences at the park include acidification of streamwaters and loss and changes in condition of sensitive species.

The prognosis for future recovery of damaged aquatic resources in Shenandoah NP was evaluated in a recent study that analyzed “critical loads” for sulfur (S) deposition (Sullivan et al. 2003 [pdf, 10.3 MB]). The critical load represents a threshold below which significant harmful effects to sensitive ecosystems components are not likely to occur. It was determined necessary for S deposition to be reduced substantially below current levels in order to prevent further acidification and associated biological impacts in acid-sensitive streams within the park.

High ridgetop ecosystems at Shenandoah NP are particularly vulnerable to the acid deposition that results from high concentrations of nitrogen and sulfur compounds. Not only do these systems receive more deposition from rain, fog, and clouds than lower elevation areas, but 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 Shenandoah NP include:

  • Acid rain with an average acidity (pH) of rainfall as low as 5.6, ten times more acidic than normal rainfall (Rice et al. 2005 [pdf, 5.7 MB]; overview summary [pdf, 546 KB]);
  • Many streams currently of pH as low as 5, ten times more acidic than the pH of park streams prior to human-caused pollution (NAPAP 1998);
  • Fewer species of fish that live in acidification-affected streams, as compared to park streams with a higher ability to neutralize acids (Bulger et al. 1999);
Image of a high elevation stream at Shenandoah NP in Virginia.
High elevation streams at Shenandoah NP in Virginia are highly sensitive to acidification resulting from nitrogen and sulfur pollution.
  • Trout species impacted by stream acidification, with particular concern regarding impacts on brook trout, and other sensitive fish including dace, chub, sculpin, darter, and bass (Webb et al. 2004; Bulger et al. 1999);
  • Aquatic insect community degradation as a result of acidification in some park streams, a particular concern given that these insects are important food sources for trout (Moeykens and Voshell 2002);
  • Soils weakened against the ability to buffer sulfur, with subsequent declines of essential nutrients calcium and magnesium, suggesting the potential that toxic aluminum could leach into streams (Welsch et al. 2001; Sullivan et al. 2003 [pdf, 10.3 MB]).

Get Sulfur & Nitrogen Data »


Ozone at Shenandoah NP and Public Health Concerns

Ground-level ozone concentrations at the park are among the highest recorded at all national parks and sometimes exceed the National Ambient Air Quality Standards set by the U.S. Environmental Protection Agency to protect public health.

Ozone is a respiratory irritant for humans. Research shows that ozone can cause coughing, sinus inflammation, chest pains, scratchy throat, and 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 have instituted an ozone advisory program aimed at educating employees and park visitors about the risks of exposure to ozone and precautions that can be taken.

Naturally-occurring ozone in the upper atmosphere forms a layer that absorbs the sun’s harmful ultraviolet rays and protects 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 inducing respiratory problems in people, elevated ozone exposures can injure plants. Ozone enters leaves through pores (stomata), where it can kill plant tissues, causing visible injury, or reduce photosynthesis, growth and reproduction.

Photo of healthy (top) and ozone-injured (bottom) Common milkweed foliage at Shenandoah NP in Virginia.
Photo of healthy (top) and ozone-injured (bottom) Common milkweed foliage at Shenandoah NP in Virginia.

Effects of ozone on vegetation at Shenandoah NP include:

  • Visible injury to leaves of trees, tree seedlings, and understory plants including black cherry, tuliptree (yellow poplar), white ash, green ash, sweetgum, milkweed, virgin’s bower, black locust, and wild grape (Sullivan et al. 2003 [pdf, 10.3 MB]; Hildebrand et al. 1996; Winner et al. 1989; Duchelle et al. 1982);
  • Reduced average height growth of yellow poplar, green ash, white ash, black locust, Virginia pine, Eastern white pine, table mountain pine, and Eastern hemlock (Duchelle et al. 1982);
  • Reduced above-ground biomass production of native vegetation (Duchelle et al. 1983);
  • Increased foliar ozone injury with increased elevation on virgin’s bower, black locust, and wild grape (Winner et al. 1989);
  • Increased foliar ozone injury with increased ambient ozone exposures on black cherry and white ash (Hildebrand et al. 1996).

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

Get Ozone Data »


Fine particles at Shenandoah 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, that 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 the 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 this haze and visibility impairment. Organic compounds, soot, and dust reduce visibility as well. Pollution-caused haze typically appears as a uniform whitish haze, different from the natural haze caused by organic compounds released by trees over the Blue Ridge Mountains of the eastern United States.

Visibility effects at Shenandoah NP include:

  • Reduction of the average natural visual range from about 120 miles (without the effects of pollution) to about 25 miles because of pollution;
  • Reduction of the visual range from about 75 miles to below 10 miles on high pollution days;
  • Human caused haze frequently impairs scenic vistas at the park.

(Source: IMPROVE 2010)

Images of good and poor visibility at Shenandoah NP, North Carolina and Tennessee (clear to hazy from left to right)
Air pollutants can affect visibility at Shenandoah NP, Virginia
(clear to hazy from left to right).

Explore scenic vistas through a live webcam at Shenandoah National Park.

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 Shenandoah NP.

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Last Updated: January 03, 2017