However, ozone found close to the surface of the earth, called ground-level ozone, is harmful air pollution. Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with relatively light winds. Even at relatively low levels, ozone may cause inflammation and irritation of the respiratory tract, particularly during physical activity. The resulting symptoms can include coughing, throat irritation, and breathing difficulty. Inhaling ozone can affect lung function and worsen asthma attacks.
Ozone can increase susceptibility of the lungs to infections, allergens, and other air pollutants.
Medical studies have shown that ozone damages lung tissue and that after exposure has ended complete recovery may take several days. In 1997, EPA strengthened national standards for ground-level ozone. The new standard, set a level of 0.08 ppm averaged over an 8-hour period, is based on the best and most recent health effects and scientific information. As EPA Administrator Carol Browner recently stated, These new standards will provide health protection to 125 million Americans, including 35 million children. Groups that are sensitive to ozone include children who are active outdoors, outdoor workers, people with respiratory diseases, such as asthma.