Amid the pines and incense cedar in Sequoia National Park, the 5 o'clock rush hour often is limited to squirrels, mule deer and the occasional skunk crossing the road.
Visitors see spectacular 13,000-foot peaks, the largest trees on the planet and far fewer idling cars than at Yosemite National Park. So the downside here seems unbelievable: Sequoia's Ash Mountain entrance this year was the worst smog trap in the country.
Worse than Fresno, Bakersfield, Los Angeles, Houston, Atlanta or any other city. With 87 days above the federal eight-hour ozone standard, the foothill entrance was in a smog cloud all summer long.
"People looking for a clean-air vacation are safer going to Los Angeles than Sequoia National Park," says Kevin Hall, executive director of the activist Central Valley Air Quality Coalition.
EDIT
http://www.fresnobee.com/2011/10/28/2594908/valley-smog-plagues-sequoia-national.html