From an article in the Los Angeles Times —
With little fanfare, Sequoia-Kings Canyon has become America’s smoggiest national park. The mountains that John Muir once described as “not clothed with light, but wholly composed of it” have on many summer days the clarity of miso soup. Grand Canyon, Joshua Tree and Great Smoky Mountains national parks get plenty of bad press for their air quality, but Sequoia-Kings Canyon would be fortunate if it had similar conditions. The pollution in Sequoia is less severe than in the Los Angeles basin, but there are more smoggy days here than in Atlanta or New York City.