Ozone

Ozone, O₃, triatomic oxygen; a blue gas with a pungent odor. It is a very powerful oxidizing agent and decomposes rapidly above 212°F (100°C). The upper atmosphere contains a layer of ozone, formed when ultraviolet radiation acts on oxygen, that protects the earth from the sun's ultraviolet rays. Ozone, made by subjecting oxygen to a high-voltage electric discharge, is used for killing germs, bleaching, removing unpleasant odors from food, and sterilizing water.