The American Lung association recently rated Knoxville as the twelfth worst city in the nation with regard to air pollution. Chronic lung disease in Knoxville and Knox county is approaching twice the national average. The chief cause of these ratings is ozone pollution.

Ozone, a colorless, slightly pungent gas, is an oxidizing agent that can sear respiratory tissue, creating scar tissue in its place. It heightens susceptibility to asthma, stuffy nose, colds, and various other forms of acute or chronic lung disease. These effects are greatest among children, asthma sufferers, and the elderly. Ozone is also toxic to certain plants.

Humans do not produce ozone directly, at least not in the high amounts found in our summer air. Ozone is, rather, a secondary pollutant created by the chemical reaction of nitrogen oxides and volatile organic compounds (which we do produce in quantity) in the presence of sunlight. The nitrogen oxides are often referred to as NO_x because their chemical formula N-O-X represents a single nitrogen (or N) atom and a variable number X of oxygen (or O) atoms. Volatile organic compounds are called VOCs for short. The NO_x and the VOCs are produced by power plants, industry and traffic.

Ironically, though we are creating too much ozone in the ground-level air we breathe, we are destroying too much in the stratosphere twenty miles above our heads. Stratospheric ozone, which protects us from the sun's cancer-causing ultraviolet rays, is thinning because we have perfused the atmosphere with chlorofluorocarbons which destroy ozone. The resultant thinning of the ozone shield is leading to increased incidence of cataracts and skin cancer. There is no practical way to move the excess ozone we are creating in the lower atmosphere up to the stratosphere where it is needed. So thoroughly have we scrambled the natural order!

Natural ozone concentrations at ground level are between twenty and forty parts per billion. According to the EPA, concentrations in excess of 80 parts per billion for eight hours are dangerous to human health. Evidence is mounting that healthy exercising adults show signs of lung damage at considerably lower exposures. The American Lung Association advocates a standard of seventy parts per billion for an eight-hour average. During the summer Knoxville frequently violates all standards. Last summer ozone levels here rose as high as 149 parts per billion.

Ozone pollution is worst during the summer, when the sunlight is most intense. In the lowlands of the Tennessee Valley, summer ozone levels vary in a daily cycle. They are highest in mid-afternoon, as sunlight and traffic combine to maximize ozone production, and lowest at night. But ozone levels in the Smokies are not so directly tied to traffic patterns. In the summer, they remain constantly high for long periods, so that mountain plants receive exposures both day and night.

As a result, the ozone problem is especially pronounced in the mountains, where we might expect to experience cleaner air. Many plant species in the Park show signs of ozone damage, ranging from leaf injury and loss to reduced growth. The coloring and shriveling of leaves that now occurs there in many species in high summer is not, except in a metaphorical sense, the harbinger of an early fall.

For many years, most researchers believed that the best way to reduce ozone formation was to lessen humanly-produced emissions of volatile organic compounds. Recently, however, it has become apparent that since natural volatile organic compounds occur naturally, limiting human emissions of VOCs may improve the ozone levels only slightly. Therefore, to significantly reduce ozone we must reduce NO_x emissions. But total NO_x emissions from internal combustion engines, industry, and TVA’s power plants are now at or near all-time highs. Reducing them may require fundamental changes in the ways we live.