CFCs (Chlorofluorocarbons)
CFCs (Chlorofluorocarbons)
Chlorofluorocarbons (CFCs), once described as "miracle chemicals," cause the breakdown of the ozone layer that protects the earth from the sun's ultraviolet (UV) radiation. CFCs have no significant natural sources. They were first manufactured in the 1930s, and industries soon found a wide variety of applications for them due to their chemical unreactivity and heat-absorbing properties. CFCs have been used as refrigerants in air conditioners and refrigerators, in aerosol spray cans, in manufacturing foams as industrial solvents , and as cleaning agents in the manufacture of electronics. One U.S. chemical industry gave them the trade name of "Freons," and the term has since become a household word.
Chemically, CFCs are a subset of the more general class of compounds known as halocarbons (carbon- and halogen-containing compounds). CFCs are halocarbons that contain only the elements carbon, chlorine, and fluorine. The most common CFCs are small molecules containing only one or two carbon atoms. For example, a common refrigerant has the chemical formula of CCl2F2, which in an industry-devised shorthand is noted as CFC-12.
Scientists initially believed that CFCs would be harmless in the earth's atmosphere because of their chemical inertness . This inertness, and their lack of solubility in water, give CFCs a long life span in the atmosphere (tens to hundreds of years, depending on the CFC). In the late 1970s, scientists began to realize that CFCs do break down in the upper atmospheric region known as the stratosphere, where the sun's UV waves are more intense. The UV-induced breakdown releases free, highly reactive chlorine and bromine atoms from the CFCs. Several subsequent chemical reactions are kick-started by this process, including the breakdown of the stratospheric ozone layer. The ozone layer is important to humans and other life on earth because it absorbs harmful UV radiation (acting as a sort of UV "shield") Long-term effects on humans' excessive UV exposure include skin cancer, eye damage (cataracts), and suppression of the immune system.
CFCs are now recognized as harmful chemicals because of their ozone-depleting properties. As a consequence, an international agreement known as the Montréal Protocol was forged in 1987 and later strengthened by amendments to decrease and eventually end the use of these chemicals. CFCs are also potent greenhouse gases and are components of pending international agreements regarding greenhouse gases, the most notable being the Kyoto Protocol (1997).
see also Global Warming; Greenhouse Gases; MontrÉal Protocol; Ozone.
Bibliography
World Meteorological Organization. (2003). Scientific Assessment of Ozone Depletion: 2002. Global Ozone Research and Monitoring Project, Report No. 47. Geneva: Author.
Internet Resources
National Oceanic and Atmospheric Administration, Climate Monitoring and Diagnostics Laboratory. "Chlorofluorocarbons." Available from http://www.cmdl.noaa.gov/noah/publictn/elkins/cfcs.html.
World Meteorological Organization. "Global Atmosphere Watch." Available from http://www.wmo.ch/web/arep/ozone.html.
Christine A. Ennis