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 about ground-level ozone, they usually picture a thick layer of smog over Los Angeles. They don't usually think of a midwest summer day-hazy blue sky, sunny, and hot. Although ozone cannot be seen or tasted, it can irritate lungs and make breathing difficult. The urban haze that we call smog contains pollutants that react to form ozone. Most of the pollutants that form ozone come from cars.