Where the Smog Ends Up: The Giant Sequoia Forest
The air in the Sierra Nevadas is getting cleaner—but the smog tide still rises every summer day.
SEQUOIA NATIONAL PARK, California—This great park in the Sierra Nevada Mountains of California attracts a million visitors a year, who come mostly in summer to see the largest trees on Earth. After Labor Day the heat and the tourists dissipate. So does a less welcome visitor: air pollution.
By a misfortune of topography, Sequoia National Park sits above an industrial-agricultural basin, the San Joaquin Valley, whose dirty, sun-baked air has nowhere to go but up. Along with its neighbor, Kings Canyon National Park, Sequoia has the worst air quality of any park in the country. In 2013 it exceeded the national health standard for ozone on 59 days, according to measurements taken at the Ash Mountain entrance station,