Opinion: The germicidal effect of ambient air (open-air factor) revisited

Abstract. The term open-air factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties attributed this to Criegee intermediates formed reaction of ozone with alkenes. We have re-evaluated those early experiments applying current state knowledge ozone–alkene reactions. Contrary previous speculation, neither nor HO radicals their decomposition are directly responsible for activity OAF. identify other potential candidates, reactions known (and likely) properties, but compounds OAF remain a mystery. There has been very little into since 1970s, effect seems largely forgotten. In opinion piece we remind community factor. Given global pandemic spread by an airborne pathogen, understanding natural effects ambient air, solving mystery determining how can be used improve human welfare should high priority atmospheric science community.