The key difference between ionizer and ozone generators is that the former typically features a number of filters to clean indoor air. Also, while air ionizers generate negatively charged nitrogen or oxygen diatomic molecules that attract particulate matter, ozone generators produces trioxygen molecules to prevent growth of bacteria.
Both ozone generators and ionizers are marketed as being able to clean indoor air, albeit through different methods. Although ozone generators can be effective at destroying infectious organisms, the necessary high concentration of ozone is toxic to humans, causing both short-term and long-term respiratory system damage. Some air ionizers also produce elevated ozone levels through operation. The Environmental Protection Agency has stated explicitly that it does not certify or recommend the use of any air-cleaning devices, whether air filters, ionizers or ozone generators.
Ozone is naturally produced in the upper atmosphere of the Earth, where it acts to filter out some of the harmful ultraviolet radiation that is emitted by the sun. At stratospheric altitudes, this compound is safe and actually protects life on the planet. Ground-level ozone, however, which is often formed by the interaction of pollutants with sunlight, is closer and breathed more often by human beings, causing harmful effects.