Chlorofluorocarbon (Cfc)
A chlorofluorocarbon (CFC) is an organic compound typically consisting of chlorine, fluorine, carbon, and hydrogen. Freon, a trade name, is often used to refer to CFCs, which were invented in the 1930s and have been used widely as aerosol propellants, refrigerants, and solvents. Odorless, colorless, nontoxic, and nonflammable, CFCs are considered valuable industrial products and have proven an especially safe and reliable aid in food preservation. However, the accumulation of CFCs in the stratosphere that may be linked to ozone depletion has generated considerable public debate and has led to legislation and international agreements (such as the Montreal Protocol and its amendments, signed by 148 countries) that banned the production of most CFCs by the year 2000. One of the substitutes developed by industry, the hydrochlorofluorocarbons (HCFCs), still contain enough chlorine to interfere with atmospheric ozone chemistry, although in much lesser amounts than CFCs. The Copenhagen amendment to the Montreal Protocol calls for the cessation of HCFC production by 2030. Hydrofluorocarbons (HFCs) are currently considered a safer substitute due to prevent ozone loss due to their lack of chlorine and shorter reactive time. As of 2002, new automobiles in the United States contain HFC refrigerant products in the air conditioners.
In the late 1920s, researchers had been trying to develop a coolant that was both nontoxic and nonflammable. At that time, methyl chloride was used, but if it leaked from the refrigerator, it could explode. This danger was demonstrated in one case when methyl chloride gas escaped, causing a disastrous explosion in a Cleveland hospital. Sulfur dioxide was sometimes used as an alternative coolant because its unpleasant odor could be easily noticed in the event of a leak. The problem was brought to the attention of Thomas Midgley Jr., a mechanical engineer at the research laboratory of General Motors. He was asked by his superiors to try to manufacture a safe, workable coolant. (At that time, General Motors was the parent company to Frigidaire.) Midgley and his associate chemists thought that fluorine might work because they had read that carbon tetrafluoride had a boiling point of 5°F (−15°C). The compound, as it turns out, had accidentally been referenced. Its actual boiling point is 198°F (92.2°C), not nearly the level necessary to produce refrigeration. Nevertheless, the incident proved useful because it prompted Midgley to look at other carbon compounds containing both fluorine and chlorine. Within three days, Midgley's team discovered the right mix: dichlorodifluoromethane, a compound whose molecules contain one carbon, two chlorine, and two fluorine atoms. It is now referred to as CFC-12 or F-12 and was marketed as Freon—as were a number of other compounds, including trichlorofluoromethane, dichlorotetrafluoroethane, and chlorodifluoromethane.
Midgley and his colleagues had been correct in guessing that CFCs would have the desired thermal properties and boiling points to serve as refrigerant gases. Because they remained unreactive, and therefore safe, CFCs were seen as ideal for many applications. Through the 1960s, the widespread manufacture of CFCs allowed for accelerated production of refrigerators and air conditioners. Other applications for CFCs were discovered as well, including their use as blowing agents in polystyrene foam. Despite their popularity, CFCs became the target of growing environmental concern by certain groups of researchers. In 1972, two scientists from the University of California, F. Sherwood Rowland and Mario Jose Molino, conducted tests to determine if the persistent characteristics of CFCs could pose a problem by remaining indefinitely in the atmosphere. Soon after, their tests confirmed that CFCs do indeed persist until they gradually ascend into the stratosphere, break down due to ultraviolet radiation, and release chlorine, which in turn affects ozone production. Their discovery set the stage for vehement public debate about the continued use of CFCs. By the mid-1970s, the United States government banned the use of CFCs as aerosol propellants but it resisted a total ban for all industries. Instead, countries and industries began negotiating the process of phasing out CFCs. As CFC use is allowed in fewer and fewer applications, a black market has been growing for the chemical. In 1997, the United States Environmental Protection Agency and Customs Service, along with other governmental agencies, initiated enforcement actions to prevent (CFC) smuggling in the United States.
Atmospheric Pollution; Global Warming; Greenhouse Gases and Greenhouse Effect; Ozone Layer and Hole Dynamics; Ozone Layer Depletion
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