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
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 extinguishing
agent, 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.
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.
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.
Methyl bromide, another
bromine-containing halocarbon, has been used as a pesticide since the 1960s.