New Recipe for Pollution Stew: Another chemical culprit adds to ozone

A chemical reaction long assumed to be unimportant in urban air quality may be a significant source of ozone, the major component of smog.

Hydroxyl (OH) radicals, among the most reactive natural chemicals in the atmosphere, help cleanse the air of some noxious pollutants. In many cases, and especially in urban environments, ozone results from that cleansing, says Amitabha Sinha, a physical chemist at the University of California, San Diego.