The Most Polluted Places In America – National Parks?

"Sequoia-Kings Canyon, where traffic jams generally involve two cars slowing to admire a mule deer, is the victim of second-hand smog. Plumes of it waft up from the Valley into the high Sierra.

But here is the real eye-opener: These adjoining national parks with soaring granite peaks and pristine meadows have more smog violations than Fresno, which sprawls to the west with almost 500,000 people"

"Smog stubbornly hangs around Giant Forest overnight, researchers said. The reason almost defies logic: It's because there is no traffic.

"While traffic does make pollutants that turn into ozone during the day, the same vehicle pollutants actually destroy ozone at night. When the sun comes up the next morning, the pollutants begin cooking into ozone again. In cities, the smog dies down from overnight traffic, scientists said."