Chlorofluorocarbons (CFCs)

Laboratory chemists first recognized CFCs as catalysts for ozone destruction in the 1970s, and atmospheric scientists observed that CFCs and their subcomponents had migrated into the lower stratosphere. When scientists discovered a zone of depleted stratospheric ozone over Antarctica, CFCs were identified as the culprit. Announcement of accelerated loss of stratospheric ozone in 1985 spurred research into the exact chemical and atmospheric processes responsible for the depletion, extensive mapping of the Antarctic and Arctic "ozone holes," and confirmation of overall thinning of the ozone layer. These discoveries also precipitated an international regulatory effort to reduce CFC emissions, and to replace them with less destructive compounds. The Montreal Protocol of 1987, and its 1990 and 1992 amendments, led to a near-complete ban on CFCs and other long-lived chemicals responsible for stratospheric ozone depletion. Atmospheric scientists predict that the phase-out of CFCs and other ozone-destroying chemicals should result in disappearance of the Antarctic ozone hole by about 2050.

CFCs are halogens, a group of synthetic compounds containing atoms of the elements fluorine, chlorine, bromine and iodine. CFC-11 (CFCl₃), CFC-12 (CF₂Cl₂), CFC-113 (CF₂ClCFCl₂), and CFC-114 (CF₂ClCF₂Cl) are the most common forms. Materials scientists first recognized the utility of CFC-12 in 1928 as a replacement for the extremely toxic sulfur dioxide, methyl-chloride, and ammonia-based refrigerants used in turn-of-the-century appliances. CFC-12 and other CFCs were then rapidly developed for other industrial applications and widely distributed as commercial products. Because of their stability, low toxicity, low surface tension, ease of liquification, thermodynamic properties, and nonflammability, CFCs were used as refrigerants in heat pumps, refrigerators, freezers, and air conditioners; as propellants in aerosols; as blowing agents in the manufacture of plastic foam products and insulation, such as expanded polystyrene and polyurethane; as cleaning and de-greasing agents for metals and electronic equipment and components, especially circuit boards; as carrier gases for chemicals used in the sterilization of medical instruments; and as dry-cleaning fluids.

CFC-11 and CFC-12 were the most widely-used CFCs. Large industrial air-conditioning equipment and centrifugal systems typically used CFC-11. Residential, automotive and commercial refrigeration and air-conditioning equipment generally contained CFC-12. Some commercial air-conditioning equipment also contained CFC-113 and CFC-114.

Emissions of CFCs to the atmosphere peaked in 1988, when air conditioners, refrigerators and factories released 690 million lb (315 million kg) of CFC-11, and 860 million lb (392 million kg) of CFC-12. At that time, about 45% of global CFC use was in refrigeration, 38% in the manufacture of foams, 12% in solvents, and 5% in aerosols and other uses. Depending on its size, a typical domestic refrigerator sold in 1988 contained about 0.4–0.6 lb (0.2–0.3 kg) of CFCs, a freezer 0.6–1.1 lb (0.3–0.5 kg), and a central air-conditioning unit about 65.5 lb (13.5 kg). About 90% of new automobiles sold in the United States and 60% of those in Canada have air conditioning units, and each contained 3–4 lb (1.4–2.0 kg) of CFCs. CFC production and use in the United States in 1988 involved about 5,000 companies in 375,000 locations, employing 700,000 people, and generating $28 billion worth of goods and services.