They do - no way around it which I would know of. I only experienced a whiff of ozone when I returned home after two weeks, with the device on all this time.

They do - no way around it which I would know of. I only experienced a whiff of ozone when I returned home after two weeks, with the device on all this time. Personally I only ever feel the irritating effect of elevated PM levels, so I keep the ionizer on. I definitely cough much less during a cold now, having the purifier, than before purchasing it.