Pale blue gas (O) that is irritating, explosive, and toxic. Like ordinary oxygen gas (O), it contains oxygen atoms, but the bonding of three atoms per molecule gives it distinctive properties. It is formed in electrical discharges and accounts for the distinctive odour of the air after thunderstorms or near electrical equipment. Usually manufactured on the spot by passing an electric discharge through oxygen or air, it is used in water purification, deodorization, bleaching, and various chemical reactions that require a strong oxidizing agent (see oxidation-reduction). Small amounts that occur naturally in the stratospheric ozone layer absorb ultraviolet (UV) radiation that otherwise could severely damage living organisms. Near Earth's surface, ozone contributes to air pollution, ozone produced by auto emissions in the presence of sunlight being a deleterious component of smog, and also accelerates the deterioration of rubber.

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