Source: air-purifiers-101.com

Lets start at the beginning before we discuss ozone air purifiers and what to watch out for. Ozone is a normal trace element that exists in the Earth's atmosphere. Activated oxygen, another name for ozone, is a three-atom form of pure oxygen (which has two atoms). When ozone comes into contact with pollutants it loses one of its atoms and "oxidizes" the pollutant, thereby destroying it.
Ozone air purifiers use electricity to produce ozone and then release into into the air to "seek and destroy" pollutants. Sounds great, but there are some important drawbacks to consider.

Some air cleaners (called ozone generators) use an electrical charge to generate ozone in an attempt to clean the air. This has been done for more than 100 years.[7] Although ozone can be used in reducing odors and pollutants in unoccupied spaces (such as removing smoke odors from homes involved in fires), the levels needed to do this are much too dangerous to breathe. The levels of ozone produced by ozone generators sold as air cleaners are too low to clean the air and too high to be healthy. Scientific research has shown that low levels of ozone will not remove indoor air contaminants.[7]