Ozone is produced by cars and trucks in exhaust. It is considered a pollutant, since it harms the eyes and the lungs. It is known to cause irritation and stinging in the eyes and coughing. Some people believe that high ozone concentrations in the air can make asthma symptoms worse in people who suffer from lung problems, and over long times can cause lung cancer. Because it is one of the more harmful pollutants, emissions of ozone from automobiles are monitored and regulated by the EPA, just as carbon monoxide and other dangerous gases are regulated. Ozone pollution is usually only a problem in large, congested cities with lots of traffic.
Ozone produced as a pollutant cannot protect us from UV exposure since UV rays reach us from above, and ozone and other pollutants are produced close to the ground and disperse rapidly. The amount of ozone produced by pollution is much much less than the amount required to absorb harmful UV rays from the sun, and much less than the amount of "good ozone" in the upper atmosphere destroyed by CFC's every year.