Ozone can purify drinking water, disinfect mildewed boats, and deodorize fire-ravaged buildings. But ozone is also a toxic gas, a component of smog, with no known beneficial health effects. The U.S. Occupational Safety and Health Administration (OSHA) limits ozone exposure in industrial settings to 100 parts per billion (ppb) over an eight-hour day, six days per week. At that level, ozone irritates the eyes, makes the throat feel dry, and stresses the lungs. The U.S. Food and Drug Administration (FDA) has set a limit of 50 ppb for the ozone from electronic air cleaners. That's a sensible limit for the home.

An ozone generator uses a high-voltage electric charge to convert oxygen in the air (O₂) to ozone (O₃), a pungent, powerful oxidant. At sufficiently high concentrations, ozone attacks and destroys gas molecules and microorganisms. Ozone has no effect on dust and other particulates, however. And ozone generators sold for home use can actually foul the air.

Given those facts, an ozone-generating air cleaner would seem a contradiction in terms. To date, Consumers Union has not found a unit that allows users to measure ozone output or to control ozone levels in a meaningful way. Some promotional materials say you can tell if ozone levels are too high when the distinctive odor becomes apparent. But research has shown that odor isn't a reliable yardstick.

When Consumers Union tested ozone generators under a variety of conditions, they almost always produced ozone levels well above the FDA's limit of 50 ppb. Although ozone generators have limited value in unoccupied spaces, it's highly questionable whether they belong where people breathe.