We hear a lot about depletion of the ozone layer in the stratosphere. This kind of ozone protects us from harmful ultraviolet radiation.
Stratospheric ozone is good, but ground-level ozone is harmful.
When people think of ground-level ozone, they usually picture a thick layer of smog over Los Angeles. It affects outlying suburbs and rural areas as well as the big cities. Ozone Action Days will be called when weather forecasters predict days that are conducive to ozone formation. The area's industries and individual residents will be asked to voluntarily reduce emissions that cause ozone pollution. The area shown on the map has a severe ozone-pollution problem.