WASHINGTON, June 24 (UPI) -- A report released Thursday by a coalition of conservation groups says bad air is choking several national parks, CNN reported.
It said almost all the pollution comes from outside sources, such as vehicle exhaust, and emissions from nearby factories and power plants.
The report also said air quality in the national parks has improved little since clean air laws were strengthened by Congress in 1990.
The report was issued by the National Parks Conservation Association, the Appalachian Voices and Our Children's Earth.
It ranked the Great Smoky Mountains National Park in Tennessee and North Carolina as the most polluted. It said unhealthy ozone levels in the park exceeded those found in cities like Washington and New York.
Other parks named in the report were Mammoth Cave National Park in Kentucky, Shenandoah National Park in Virginia, Acadia National Park in Maine and Sequoia-Kings Canyon National Parks in California.
"Unless we do something to strengthen the Clean Air Act -- which won't include the President's Clear Skies Plan -- not only will we see ozone get worse, but (so will) the acidification of streams and soils and the cascade of ecological effects," said spokesman Harvard Ayers.