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Scenic views and native vegetation images from parks within Cumberland Piedmont Network

Air Pollution Impacts

Mammoth Cave National Park

Natural and scenic resources in Mammoth Cave National Park (NP) are susceptible to the harmful effects of air pollution. Fine particles, ozone, nitrogen, sulfur, and mercury, impact scenic resources such as visibility, and natural resources such as wildlife, surface waters, and vegetation. Click on the tabs below to learn more about air pollutants and their impacts on natural and scenic resources at Mammoth Cave NP.

  • Visibility
  • Ozone
  • Nitrogen & Sulfur
  • Toxics & Mercury

Fine particles at Mammoth Cave 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 by a source, such as power plants, or reactions with gases and aerosols in the atmosphere emitted from sources upwind. 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.

Visitors come to Mammoth Cave NP not only to explore the vast and complex underground labyrinths, but to enjoy vistas of the Green River valley and hill country of South Central Kentucky. Unfortunately, such views are sometimes 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.

Images of good and poor visibility at Mammoth Cave National Park, Kentucky
Air pollutants can affect visibility at Mammoth Cave NP, Kentucky (clear to hazy from left to right)

Visibility effects at Mammoth Cave NP include:

  • Reduced visibility due to human-caused haze and fine particles of air pollution;
  • Reduction of the average natural visual range from about 110 miles (without the effects of pollution) to about 20 miles because of pollution at the park;
  • Reduction of the visual range to below 10 miles on high pollution days.

(Source: IMPROVE 2010)

Explore scenic vistas through a live webcam at Mammoth Cave National Park.

Get Visibility Data »


Photo of healthy (top) and ozone-injured (bottom)  Common milkweed at Mammoth Cave NP in Kentucky.
Photo of healthy (top) and ozone-injured (bottom) common milkweed foliage at Mammoth Cave NP, Kentucky.

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

There are several ozone-sensitive plants in Mammoth Cave NP including Asclepias syriaca (common milkweed), Liquidambar styraciflua (sweetgum), and Liriodendron tulipifera (tulip poplar). Recent assessments documented foliar ozone injury on approximately 25% of the Common milkweed plants surveyed (CUPN 2010). Sweetgum and Tulip poplar have also exhibited foliar ozone injury.

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

Ozone and Public Health Concern

Ground-level ozone concentrations at the park 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, 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.

An ozone advisory program at Mammoth Cave NP educates employees and park visitors about the risks of exposure to high ozone levels and precautions to reduce exposure.

Get Ozone Data »


Photo of buffalo creek at Mammoth Cave NP, Kentucky
Surface waters atop of sandstone ridges at Mammoth Cave NP, Kentucky, may have little buffering capacity against acid deposition.

Nitrogen and sulfur compounds deposited from air pollution can harm surface waters, soils, and vegetation. While the seeps and surface waters that emanate from the limestone bedrock are well-buffered from acidification effects, some soils, the sandstone ridges, and dry upland areas may be sensitive to acid deposition. There is a particular concern that during rainstorms, when there is little opportunity for rainwater to come into contact with deep soils, episodic acidification could occur. Nitrogen and sulfur deposition can acidify soils and surface waters. In addition to acidification effects, nutrient effects from nitrogen deposition can cause changes to soil nutrient cycling and the species composition of plant communities in some ecosystems.

Get Nitrogen & Sulfur Data »


Photo of a scientist holding a bat.
Hair from bats at Mammoth Cave NP in Kentucky is sampled to analyze mercury levels.

Toxics, including heavy metals like mercury, accumulate in the tissue of organisms. When mercury converts to methylmercury in the environment and enters the food chain, effects can include reduced reproductive success, impaired growth and development, and decreased survival. Other toxic air contaminants of concern include pesticides, industrial by-products, and emerging chemicals such as flame retardants for fabrics, some of which are also known or suspected to cause cancer or other serious health effects in humans and wildlife.

Coal-burning power plants are the major sources of mercury to the atmosphere. Numerous nearby coal-fired power plants likely contribute to increased mercury deposition at Mammoth Cave NP. Kentucky has already issued a statewide mercury fish consumption advisory. Mercury deposition at the park is relatively high, likely indicative of large nearby sources of mercury (NPS 2010 [pdf, 2.8 MB]). Elevated levels of mercury have been found in bat, fish, insect, water, and sediment samples in the park (NPS 2009).

Get Mercury 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 Mammoth Cave NP.

Related Links

Last Updated: December 30, 2016