Americans who have been thinking about escaping to a national park for some fresh, clean air may want to think again.
Unhealthy levels of smog have been measured in seven national parks, according to National Park Service officials. Among them are some of the most famous and popular ones, such as Yosemite in California and Shenandoah in Virginia.
''Visitors to the parks might expect they can escape urban pollution,'' says Brian Mitchell, an air-quality expert for the park service. ''But they're being exposed to air quality that's not very healthy.''
Smog, also known as ozone, causes lung irritation. It has been linked to asthma, bronchitis and pneumonia. It forms when pollutants emitted by vehicles, power plants and factories are exposed to sunlight.
Nearly all of the smog in the parks blows in from someplace else. In Great Smoky Mountains National Park in Tennessee and North Carolina, a study by the Park Service found that on days when the park's air is unhealthy, 20% to 50% of the smog came from nearby Knoxville, Tenn.
Next week, the EPA will release a list of every county in the nation that has unhealthy levels of smog. The list will include the parks, Park Service officials say.
Counties on the EPA's list must take steps to improve their air quality. Such steps might include increasing public transportation and requiring local industry to reduce emissions.
The EPA also is working on a plan to clean up the haze that shrouds the views in many national parks. The details are unclear, but the plan is likely to require cuts in the pollutants that form haze.
Many pollutants that form haze also contribute to smog. So the haze rule -- which the agency will publish next week -- may also help reduce smog in the parks.
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