List of US national parks with highest smog levels

FRESNO, Calif. - Sequoia National Park, home to the giant redwoods, suffers the worst air pollution of any national park in the country. Here are the parks in the National Park Service system with the highest smog levels and the number of days monitors recorded violations last year:

— Sequoia National Park, Calif.: 87.

— Joshua Tree National Park, Calif.: 56.

— Great Smoky Mountains National Park, N.C.: 12.

— Yosemite National Park, Calif.: 8.

— Rocky Mountain National Park, Colo.: 8

— Big Bend National Park, Texas: 7.

— Mojave National Preserve, Calif.: 6

An ozone reading of 75 parts per billion or higher, which the EPA says is "unhealthy for sensitive groups," is considered a violation of the agency's regulations. The following parks exceeded that level in 2011:

— Sequoia National Park, Calif.: 98 ppb (unhealthy for everyone)

— Joshua Tree National Park, Calif. 91 ppb (unhealthy for everyone)

— Great Smoky Mountains National Park, N.C.: 83 ppb (unhealthy for sensitive groups)

— Big Bend National Park, Texas: 80 ppb (unhealthy for sensitive groups)

— Yosemite National Park, Calif.: 79 ppb (unhealthy for sensitive groups)

— Mojave National Preserve, Calif.: 78 ppb (unhealthy for sensitive groups)

— Rocky Mountain National Park, Colo.: 77 ppb (unhealthy for sensitive groups)

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Sources: National Park Service and Environmental Protection Agency