An air purifier has a perforated plate between UV lamps on the one hand and a porous air filter on the other. Biological material is trapped by the filter and eventually killed by the low dose of UV radiation which passes through the perforations in the plate. Filtered air passing through the plate is subjected to a high dose of UV radiation which sterilizes remaining biological material in the air. An electrostatic filter at the outlet may trap viruses which have been positively charged either by the action of the UV lamps or by positively charging the plate in order to strip electrons from the viruses. The UV lamps may be mercury lamps which are allowed to emit at both their ozone forming wavelength as well as the ozone breakdown wavelength. In such instance, a light filter surrounds the lamps which passes light only at the ozone breakdown wavelength. Air subjected to the unfiltered light is consequently subjected to ozone, which is a known biocide. The filtered light is in a zone which is filled with water mist such that hydroxyl radicals result. Air passing through this zone is scrubbed by the hydroxyl radicals.