Air in the Great Smoky Mountains
The blue gray mist that lingers over the Great Smoky Mountains National Park is created by both natural and artificial sources.
On this day in 1940, President Franklin D. Roosevelt dedicated the opening of the Great Smoky Mountains National Park (GSMNP). Roosevelt had in mind protecting the scenery and natural resources so that Americans might enjoy and appreciate their natural heritage. With more than 140 native species of trees, 4,000 species of plants, over 850 miles of scenic hiking trails, and 2,100 miles of streams and rivers, the Great Smoky Mountains represents one of our nation’s most pristine and diverse natural areas, and was designated an International Biosphere Reserve in 1976. But most of all, people love the blue gray mist that hangs over the peaks and fills the valleys, giving the Smoky Mountains a unique chemistry of air.
Both the Smoky Mountains and the Blue Ridge Mountains, which lie to the north in Virginia, are part of the Appalachian mountain chain. Both were named long before the modern influences of air pollution. And both are characterized by conifer forests, whose pine needles release an organic compound called terpenes. Terpenes are an ingredient of turpentine, and also a building block for the essential oils of many plants and trees. Once released to the air, terpenes undergo a photochemical reaction with ozone to produce particulates, which in turn reflect a limited section of the visible spectrum of light. In other words, the blue color we see is a reflection of the terpenes reacting with natural ozone.
Sadly, the increasingly hazy views are not attributed to natural sources. While the Smoky Mountains have no major pollution sources nearby, winds blowing toward the southern Appalachians bring with them the emissions from industry and power plants burning fossil fuels. As the winds are halted by the barrier of the mountains, those emissions tend to collect in and around the park. The Smoky Mountains demonstrate that degrading air quality conditions are a result of regional air pollution issues – with air, ‘local’ doesn’t mean very much. Although photochemical smog is often associated with cities, the ground level ozone produced in smog reactions takes time to form, and thus, it often collects downwind of the original pollution sources. Numerous plant species in the national park, especially those at high altitude, show symptoms of significant ozone damage, some of the highest ozone levels in the East. These high elevation plants and trees are further stressed as a result of industry emissions of nitrogen oxide and sulfur oxide, which create extremely acidic rain, snow, mist, and clouds. The low pH of the precipitation further stresses plants and trees, leaving them less resilient, and the ecosystem at even greater risk. Lower overall air quality also significantly reduces the visibility from scenic outlooks.
Still, the presence of the GSMNP provides a space where the impact of these air quality issues can be investigated. Identifying a problem is an essential first step in solving it, and the ongoing, scientific investigations in the Smokies show clearly how certain emissions affect the environment. Some days are clearer than others, but today’s visitors are less likely to enjoy the breathtaking views that were present when the park was founded; the health of the whole Great Smoky ecosystem has been affected by human activities. Hopefully, the clear days and still beautiful scenery will serve as motivation to leave a gentler footprint on our environment for the future.
More information is available at http://www.nps.gov/grsm/naturescience/environmentalfactors.htm