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Ozone Depletion

Ozone Depleting Chemicals

The most commonly known ozone depletion chemicals (ODCs) are the CFCs or chlorofluorocarbons. Over the last 30 years man-made CFCs have been the main cause of stratospheric ozone depletion. Fortunately, CFCs, once used for example in refrigeration, air conditioning, and fire extinguishers, have been largely phased out in the aftermath of the Montreal Protocol.

CFCs however, are not the only ozone-depleting chemicals. Other ODCs include the methylhalides, carbon tetrachloride (CCl4), carbon tetrafluoride (CF4), and the halons which contain bromine instead of chlorine. Such compounds are called halocarbons.

Carbon tetrachloride (CCl4), despite its toxicity, was first used in the early 1900s as a fire extinguishant, and more recently as an industrial solvent, an agricultural fumigant, and in many other industrial processes including petrochemical refining, and pesticide and pharmaceuticals production. Recently it has also been used in the production of CFC-11 and CFC-12. It has accounted for less than 8% of total ozone depletion. The use of carbon tetrachloride in developed countries however, has been prohibited since the beginning of 1996 under the Montreal Protocol.

Methyl chloroform, also known as 1,1,1 trichloroethane is a versatile, all-purpose industrial solvent used primarily to clean metal and electronic parts. It was introduced in the 1950s as a substitute for carbon tetrachloride. Methyl chloroform has accounted for roughly 5% of total ozone depletion. The use of methyl chloroform in developed countries has been prohibited since the beginning of 1996 under the Montreal Protocol.

Halons, unlike CFCs, contain bromine, which also destroys ozone in the stratosphere. Halons are used primarily in fire extinguishers. Halon-1301 has an ozone depleting potential 10 times that of CFC-11. Although the use of halons in developed countries has been phased out since 1996, the atmospheric concentration of these potent, ozone destroyers is still rising because of their long atmospheric lifetimes. To date halons have accounted for about 5% of global ozone depletion.

Methyl bromide, another bromine-containing halocarbon, has been used as a pesticide since the 1960s. Today, scientists estimate that human sources of methyl bromide have been responsible for approximately 5 to 10% of global ozone depletion.