ozone

—ozonic /oh zon"ik, oh zoh"nik/, adj.

/oh"zohn, oh zohn"/, n.

a form of oxygen, O₃, with a peculiar odor suggesting that of weak chlorine, produced when an electric spark or ultraviolet light is passed through air or oxygen. It is found in the atmosphere in minute quantities, esp. after a thunderstorm, is a powerful oxidizing agent, and is thus biologically corrosive. In the upper atmosphere, it absorbs ultraviolet rays, thereby preventing them from reaching the surface of the earth. It is used for bleaching, sterilizing water, etc.

[ < G Ozon < Gk ózon, prp. of ózein to smell; see OZO-]

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Pale blue gas (O₃) that is irritating, explosive, and toxic.

Like ordinary oxygen gas (O₂), 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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▪ chemical allotrope

      (O₃), triatomic allotrope of oxygen (a form of oxygen in which the molecule contains three atoms instead of two as in the common form) that accounts for the distinctive odour of the air after a thunderstorm or around electrical equipment. The odour of ozone around electrical machines was reported as early as 1785; ozone's chemical constitution was established in 1872. Ozone is an irritating, pale blue gas that is explosive and toxic, even at low concentrations. It occurs naturally in small amounts in the Earth's stratosphere, where it absorbs solar ultraviolet radiation, which otherwise could cause severe damage to living organisms on the Earth's surface. Under certain conditions, photochemical reactions between nitrogen oxides and hydrocarbons in the lower atmosphere can produce ozone in concentrations high enough to cause irritation of the eyes and mucous membranes.

      Ozone usually is manufactured by passing an electric discharge through a current of oxygen or dry air. The resulting mixtures of ozone and original gases are suitable for most industrial purposes, although purer ozone may be obtained from them by various methods; for example, upon liquefaction, an oxygen-ozone mixture separates into two layers, of which the denser one contains about 75 percent ozone. The extreme instability and reactivity of concentrated ozone makes its preparation both difficult and hazardous.

      Ozone is 1.5 times as dense as oxygen; (oxygen) at -112° C (-170° F) it condenses to a dark blue liquid, which freezes at -251.4° C (-420° F). The gas decomposes rapidly at temperatures above 100° C (212° F) or, in the presence of certain catalysts, at room temperatures. Although it resembles oxygen in many respects, ozone is much more reactive; hence, it is an extremely powerful oxidizing agent, particularly useful in converting olefins into aldehydes, ketones, or carboxylic acids. Because it can decolorize many substances, it is used commercially as a bleaching agent for organic compounds; as a strong germicide it is used to sterilize drinking water as well as to remove objectionable odours and flavours. See also ozonosphere.

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