Ozone has recieved a bad rep recently, mainly due to the summer-time smog issues primarily in California. In actuality, smog is a combination of hydrocarbons and VOC's (Volatile Organic Compounds) which inundate areas with larger amounts of pollution. Ozone IS NOT smog; it is, in fact, naturally ocurring. Ozone is present in smog, but the process that creates this pollution also creates smog. The more pollution you have, the more smog is created. Ozone is present to help clean the pollution, and without it we would not be able to life safely in our cities. Unfortunately, Ozone has been getting a bad rep when in fact it is the hydrocarbons and VOC's, along with the many other toxic and harmful particulates in the air.
For more information on what Ozone is and how it is actually GOOD for us to have around, read this article Ozone is Good and Natural.