I know that every electric motor produces some ozone, it's unavoidable. Most of the time I don't notice it. We had a Honeywell HEPA room air purifier (basically a fan which pulls in room air through a carbon prefilter and a nested HEPA filter, traps most dust and pollen) in the kids' room for years with no problem, changing filters as necessary, but last year the room started smelling more and more like ozone whenever the purifier was on. Finally it got to the point where I'd start coughing as soon as I stepped into the room.
Hoping that it was just a motor going bad, we bought two more air purifiers, from different stores -- and both of them started producing an ozone smell after a day also.
Fortunately my kids aren't suffering from allergies currently so we've just turned it off.
Any ideas what's going on?