It's a harmless-looking pale blue gas, a relative of the oxygen molecule that sustains life. In the upper atmosphere, a layer of it protects us from the sun's harmful rays.
But ozone molecules, composed of three oxygen atoms, can trigger breathing problems when they form near the ground, said David Peden, MD, director of the Center for Environmental Medicine, Asthma and Lung Biology at the UNC School of Medicine.
Ozone pollution is more common during "ozone season," which begins in April and peaks in the warm summer months. Ozone forms on hot, sunny days when pollutants from car exhaust, power plants, gas stations and industrial facilities undergo chemical reactions in sunlight. Meanwhile, the stagnant weather systems that often form in summer can trap pollution around a community.
More than half of North Carolina's residents live in counties where ozone levels sometimes reach unhealthy levels, according to the N.C. Department of Environment and Natural Resources. Children, people with respiratory diseases and healthy adults who exercise or work outdoors are at risk.
Peden investigates the health effects of ozone at the Environmental Protection Agency Human Studies Facility located on the UNC-CH campus. His team uses controlled chambers to expose volunteers to varying levels of air pollutants. That research has shown that exposure to ozone inflames the lungs, which can aggravate other breathing problems.
"Those changes can exacerbate other issues," he said. "The person is subsequently more likely to have an asthma attack or be more reactive to allergens." Those responses often do not appear until the day after ozone exposure, he said.
In addition, Peden said that a study of southern California children suggested that long-term, chronic exposure to ozone may affect lung development. Ozone may also be linked to cardiovascular disease, an area of research that Peden is now pursuing.
To protect themselves on elevated-ozone days, Peden said individuals should avoid outdoor air in the afternoon, when ozone levels peak.
"Do most of your vigorous outdoor work in the morning or in the evening, after the ozone has decreased," he said.