Air Quality

Nature and Science
View from Bluff Mountain Overlook

(NPS Photo - Bob Cherry)

Visitors have traveled the Parkway for years enjoying majestic views and distant horizons. Increasingly however these views have become less and less majestic as pollution gets in the way and haze blocks the distant scenes.

There has always been some pollution affecting the views in the Southern Appalachians. In fact the Blue Ridge Mountain’s name originated because of the bluish haze caused by hydrocarbons released by trees into the atmosphere. However, over the last 50 years the visibility in the Southern Appalachians has decreased 40% in the winter and 80% in the summer because of man-made pollutants.

Most of the pollution is caused by power plants, industry and automobiles. These pollutants come from both within and outside the Southern Appalachians, often traveling hundreds of miles. As the winds bring the pollutants to the Blue Ridge the mountains trap and concentrate them. While the decreased views are noticeable, there are also other impacts that cannot be seen.

Acid rain is probably the most familiar type of air pollution problem for most people. Acid rain is just one type of acid deposition, or the introduction of acid from the atmosphere to the ground. It is made up of sulfuric acid, nitric acid and ammonia, which are made from sulfur dioxides (SO2), nitrogen oxides (NOx), and ammonium (NH3) which in turn are emitted from burning fossil fuels, primarily as emissions from electric utilities and motor vehicles, and from agricultural activities.

In addition to acid rain, acids are brought to the ground as snow, dry particles, clouds and fog. Studies in the Great Smoky Mountains National Park have found that average rainfall there is 5-10 times more acidic than normal rain and that clouds covering the mountain tops are often 100 times more acidic still.

Several problems result from this acidification of the Blue Ridge and other areas in the Eastern US. There is increasing evidence that soils are being altered in many areas. So much nitrogen is being deposited that soils are becoming nitrogen saturated. This leads to the loss of calcium in the soil, which affects plant nutrition, and the release of aluminum which can be toxic to plants, fish and other organisms. The accumulation of sulfur and nitrogen in the soil also leads to acidification of streams and lakes as they leach out with flowing water.

Acidification can also cause stress on vegetation resulting in poor crown condition, reduced tree growth and high levels of tree death. Acid deposition has been linked with the decline in red spruce trees, leaching calcium from the tree’s needles and making them more susceptible to freezing. Increased aluminum in the soil may limit a spruce tree’s ability to take up water and nutrients through its roots.

Ozone is another pollutant that the winds carry to the Blue Ridge Parkway. Ground level ozone is created when the nitrogen oxides mix with hydrocarbons in sunlight. Ozone levels at ridgetops in the Smokies have been found to be twice the levels found in Atlanta and Knoxville. In addition to causing health problems in humans, ozone is also harmful to vegetation. Leaves of many species are damaged after exposure to high levels of ozone, with increased damage at higher elevations.

Last updated: April 14, 2015

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