Chlorofluorocarbons (CFCs) are a group of anthropogenic compounds which are widely used as refrigerants, aerosol propellants, plastic foam blowing agents and solvents. Although often popularly referred to by’ the Dupont tradename “freons,” these compounds are produced worldwide by a number of manufacturers. CFCs have low toxicity, are not very reactive under normal conditions, and have a variety of useful physical properties. Production of two of these compounds, dichlorodifluoromethane (F-12) and trichlorofluoromethane (F-11), began in the early 1930s. Industrial production of F-11 and F-12 accelerated during the following three decades as demand for these compounds grew. CFCs are volatile, and most of the F-11 and F-12 produced eventually enters the atmosphere. In some applications, such as the use of F-I1 and F-12 as aerosol propellants, the typical delay between production and release of the CFC to the atmosphere is relatively short, but for other uses, such as in hermetically sealed refrigeration systems, the average delay until release can be a decade or longer.

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