About 167.3 million Americans encounter unhealthy levels of ozone, the most widespread outdoor pollutant, says the American Lung Association's State of the Air 2010 report. Inhaling ozone can cause wheezing, coughing, chest pain, throat irritation, congestion, and can make people more susceptible to respiratory illnesses such as bronchitis and pneumonia, according to the U.S. Environmental Protection Agency. For those with bronchitis, emphysema, or asthma, ozone is particularly troublesome, since it can limit lung function and cause inflammation in the lining of the lungs. Repetitive exposure to ozone over time can even permanently scar lung tissue, says the EPA.
Still, ozone can be tough to avoid. It's the byproduct of pollutants released by cars, chemical plants, industrial boilers, refineries, and other sources. Ozone exists naturally in the upper atmosphere of the Earth, but when emitted at ground level, it's considered a harmful outdoor pollutant. Ozone pollution is more common during warmer months because more sun is present, which helps create ground-level ozone.
But there are precautionary steps you can take to limit your exposure to harmful levels of ozone, particularly when you plan to exercise outdoors. The longer you are active outdoors and the more strenuous your activity, the more likely you are to be affected by ozone. When unhealthy ozone levels are present in your city:
- Limit time spent doing physical activity outdoors.
- Schedule outside activities for morning or evening, when ozone levels are lower.
- Do less strenuous activity outdoors. Go for a walk instead of a run, for example.
Know where your city stands. The American Lung Association's State of the Air 2010 lists these 10 cities as the country's most polluted by ozone:
- Los Angeles, Calif., metropolitan area (including Long Beach and Riverside)
- Bakersfield, Calif.
- Visalia and Porterville, Calif.
- Fresno and Madera, Calif.
- Sacramento, Calif., metropolitan area (including Arden-Arcade and Yuba City)
- Hanford and Corcoran, Calif.
- Houston, Texas, metropolitan area (including Baytown and Huntsville)
- San Diego, Calif., metropolitan area (including Carlsbad and San Marcos)
- San Luis Obispo and Paso Robles, Calif.
- Charlotte, N.C., metropolitan area (including Gastonia and Salisbury)