Ozone is a pale blue gas with a distinctively pungent smell. Ozone gas is a powerful oxidant and has many industrial and consumer applications related to oxidation. This same high oxidising potential, however, causes ozone to damage mucous and respiratory tissues in animals, and also tissues in plants, above concentrations of about 100 ppb. This makes ozone a potent respiratory hazard and pollutant near ground level.
Ozone gas odour is sharp, reminiscent of chlorine, and detectable by many people at concentrations of as little as 10ppb in air.