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Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs)

CFCs are a family of man-made gases used for various industrial purposes. First developed in the 1920's in the United States, CFCs have been used in large quantaties since 1950. The industrialized countries can account for over 80% of CFCs use. CFC-11 is used primarily as a propellant in aerosol cans, although its use has been phased out it is still used in the production of plastic foams. CFC-12 is used in foam production as well as cooling coals of refrigerators and air conditioners. HCFC-22 was recently introduced as a replacement for CFC-12 because of its shorter life in the atmosphere, and thus is less of an ozone depleting drug. CFC-113, methyl chloroform, and carbon tetrachloride are used as solvents for cleaning, carbon tetrachloride is also a feed stock for the production of CFC-11 and CFC-12.
    CFCs are released in relatively small quantities, but one kilogram of the most common CFCs may have a direct effect on climate 1000 times large than that of one kilogram of carbon. In addition over the last two decades the percentage increase of CFCs in the atmosphere has been higher than any other greenhouse gas. By 1990 the increase was 4-12% a year.
CFCs also destroy ozone - itself a greenhouse gas - their net effect on climate is unclear. The strength of the indirect effect of ozone depletion depends on variables such as temperature of the upper atmosphere and cannot yet be measured with any confidence. According to new research, however, it is possible that the indirect effect of CFCs cancels out some or all of the direct effect of their being powerful greenhouse gases.
CFCs are generally colorless, odorless, and non-toxic. They also do not react chemically with other materials, and as a result they remain in the atmosphere for a very long time -- often 50 to 100 years -- before they are destroyed by reactions catalyzed by the sunlight. CFCs are composed of carbon, chlorine, and fluorine. Together with other manufactured gases that contain either fluorine or chlorine, and with bromine-containg Halons, CFC's are referred to collectively as halogenated compounds, or halocarbons.
    There is an often significant lag time

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