Straddling the border of North Carolina and Tennessee, Great Smoky Mountains National Park protects 800 square miles of the southern Appalachian Mountains. It is the largest federally protected upland landmass east of the Mississippi River.  Air pollution, however, does not recognize these human-drawn borders. While traveling in the Smokies recently, I learned more about the air quality issues facing this country’s most visited national park.

According to the NPS, most of the air pollution impacting the park originates outside its boundaries. Emissions of sulfur dioxide and nitrogen oxides from power plants, factories, and vehicles are the main sources. Carried by wind to the southern Appalachians, the height of the mountains and the prevailing weather patterns of the region tend to trap the pollution in and around the park.

Originally named for its naturally occurring smoke-like blue haze, the park in recent years has been shrouded by unnatural white smog. Produced by tiny sulfate particles – released into the air by the burning of fossil fuels – the smog scatters light and reduces visibility. It has degraded views from the park’s scenic mountain overlooks and dulled its signature blue haze. Since 1948, according the NPS, human-made pollution has decreased average visibility in the region by 40% in winter and 80% in summer.

Ground level ozone, formed when nitrogen oxides react with heat and U.V. light, is known to have negative impacts on human health.  In the Smokies, it is also injuring trees and plants. Damaging leaves, it reduces photosynthesis and limits a plant’s ability to produce and store food.  As a result, they are more susceptible to disease, insects, and extreme weather events.

Acid rain is another problem for the park that is rooted in air pollution. It develops when sulfur dioxide and nitrogen oxides react with water and oxygen in the atmosphere to form solutions of sulfuric acid and nitric acid. This type of precipitation alters the chemistry of forest soils and streams. It jeopardizes the health of entire ecosystems, as a large array of species – from fish to trees – cannot adapt to the more acidic conditions. The average pH of rainfall in the Smokies, according to the NPS, is 4.5. That is 5–10 times more acidic than the pH range of normal rainfall.

While air quality issues in the park – like much of the rest of the country – have improved in recent years, it still remains a serious problem. Addressing the matter, the NPS says: “The Park Service is working with state regulatory agencies, the Environmental Protection Agency, and industrial and utility interests to develop a comprehensive plan to prevent future damage through such measures as offset programs, the use of improved technology, and determination of emission caps and government standards for various pollutants. To remedy air pollution problems at the park, additional reductions of nitrogen oxides and sulfur dioxide are necessary.”