In one aspect, ozone is quenched from a water stream, such as a drinking water or wastewater stream being treated with ozone, by contacting the stream with magnesium thiosulfate. In another aspect, a method of scrubbing ozone from a gaseous stream comprises contacting the gaseous stream with magnesium thiosulfate. In an alternative embodiment, chlorine is quenched from a water stream by contacting the stream with magnesium thiosulfate or potassium thiosulfate. In yet another aspect, a method of scrubbing chlorine from a gaseous stream comprises contacting the stream with magnesium thiosulfate or potassium thiosulfate. In another embodiment, a thiosulfate, such as magnesium thiosulfate, calcium thiosulfate, potassium thiosulfate, or sodium thiosulfate, is provided on an air filter for scrubbing ozone or chlorine from gaseous streams.