Ozone, a lung irritant, is produced indirectly by ion generators and some other electronic air filters and directly by ozone generators. While indirect ozone production is a matter of concern, there is even greater concern with the direct and deliberate introduction of a lung irritant into indoor air. Despite some vendors' claims, there is no difference between ozone in outdoor smog and ozone produced by these devices. Under certain conditions of use, ion generators and other air purifiers that generate ozone can produce levels of this lung irritant significantly above levels considered harmful to human health.
A small percentage of air purifiers claiming a health benefit may be regulated by the FDA as a medical device. The Food and Drug Administration has set a limit of 0.05 parts per million ozone for medical devices. Although ozone can be used to reduce odors and pollutants in unoccupied spaces (such as removing smoke odors from homes involved in fires), the levels needed to achieve this are above those generally believed to be safe for humans. Indoors, ozone is produced by air ionizers (if you have one in your home).
As mentioned above, ionizers commonly use corona discharge to emit negative ions. However, the gas emitted by the corona discharge can be toxic to humans and the environment (. Some ozone air purifiers are manufactured with an ion generator, sometimes called an ionizer, in the same unit. You can also purchase ionizers as separate units.
Ionizers remove particles from the air. They do this by causing particles to adhere to nearby surfaces or to each other and deposit out of the air, but they can generate unwanted ozone. If you've come this far and digested all the information about air ionizers (whether they're marketed as ionic air purifiers or ionizers), you've probably already realized that most people shouldn't buy an air purifier with an ionizing function.