Some wind-borne pollutants found in the Southern Appalachians come from as far away as the Mississippi River Valley and the Gulf Coast. The unique topography and predominant weather patterns of the region tend to trap air currents exposing the Southern Appalachians to prolonged periods of poor air quality. The two major pollutants affecting the region are ground-level ozone and acid deposition. Ozone is formed by the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight. In humans, ozone lowers resistance to disease and increases the incidence and severity of respiratory ailments.
Plants show parallel symptoms.
Their resistance to disease and pests is decreased. Ozone breaks down cell membranes in the leaves of plants inhibiting their respiratory function and photosynthesis. Field surveys in the Great Smoky Mountains National Park have identified 90 species of plants that exhibit ozone-like symptoms. Sulfur dioxide and oxides of nitrogen react in the atmosphere with water, oxygen, and oxidants to create acid rain and acid deposition. The Southern Appalachians receive some of the highest acid deposition in North America.