Chlorofluorocarbons and the ozone
Chlorofluorocarbons (CFCs) are a family of chemical compounds composed of chlorine, fluorine, and carbon. Initially discovered in 1928, CFCs became popular for use in air conditioning, refrigeration, and as propellants in aerosol spray cans due to their stability and ease of liquefaction. However, concerns arose regarding their impact on the ozone layer, which protects the Earth from harmful ultraviolet (UV) radiation. Research in the 1970s linked CFCs to ozone depletion, as they can release chlorine atoms in the stratosphere that catalytically destroy ozone molecules. This depletion can lead to increased UV exposure, potentially causing higher rates of skin cancer and ecological damage.
The growing evidence prompted several regulatory actions, starting with bans in individual U.S. states and culminating in the 1987 Montreal Protocol, an international agreement aimed at phasing out CFCs by 2010. Subsequent amendments to the Clean Air Act in the U.S. expedited these restrictions. By the mid-1990s, CFC levels in the atmosphere began to stabilize, and they are expected to gradually diminish over the coming century, reflecting a significant global effort to protect the ozone layer.
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Chlorofluorocarbons and the ozone
DEFINITION: Family of chemical compounds used in air conditioners, refrigerators, and aerosol spray cans
Concerns about the destruction of stratospheric ozone by chlorofluorocarbons led to a worldwide ban on the manufacture and use of these compounds.
Chlorofluorocarbons (CFCs) are molecules containing chlorine, fluorine, and carbon atoms. The first CFCs were discovered by Thomas Midgley, Jr., in 1928. Because these molecules are chemically inert and easily liquefied, CFCs soon became the standard coolants in refrigerators and air conditioners. They also became widely used as propellants in spray cans. By 1968, 2.3 billion aerosol cans containing CFCs had been sold in the United States.
In 1970 the British scientist James Lovelock determined that most CFCs entering the atmosphere remained there without significant decomposition. Three years later, Frank Sherwood Rowland and Mario Molina, working at the University of California at Irvine, suggested that CFCs would eventually migrate into the stratosphere. Once there, of ultraviolet light would cause CFCs to chlorine atoms, which would then react catalytically to remove ozone. Since ozone in the prevents high-energy ultraviolet light from reaching the surface of the earth, any decrease in ozone would lead to increased to ultraviolet light on the earth’s surface, causing higher levels of skin cancer in humans and damage to plants and animals.
Although evidence from laboratory studies suggested that CFCs in the atmosphere would cause depletion of stratospheric ozone, uncertainty remained as to the degree of ozone destruction that would occur. Nevertheless, in 1975 Oregon became the first US state to ban CFCs in aerosol spray cans. Several other states took similar actions, and in 1977 the Food and Drug Administration (FDA) implemented a ban on the use of CFCs as aerosol propellants to be phased in over a two-year period. Continued uncertainties in predictions of ozone loss and the lack of direct evidence for ozone depletion kept most other countries from restricting the use of CFCs. While the U.S. Environmental Protection Agency (EPA) discussed instituting a total ban on CFCs, no action was taken, in part because of the difficulty in finding adequate substitutes for CFCs.
In 1985, a team of British scientists led by Joseph Farman announced the discovery of significant loss of ozone over the Antarctic. Beginning in the early 1970s, springtime levels of ozone had slowly decreased. By 1985, as much as 40 percent of the ozone usually present in the Antarctic stratosphere during the spring had disappeared. In addition, both the duration and the geographic extent of this were increasing. Evidence linking formation of the ozone hole to CFCs in the atmosphere was quickly found.
The discovery of the ozone hole led to further restrictions on CFCs. In 1987 an international agreement called the Montreal Protocol was reached to ban the manufacture and use of CFCs by the year 2010. In the United States, passage of the 1990 Clean Air Act amendments resulted in an accelerated timetable for restrictions on CFCs and related compounds. By the mid-1990s, levels of CFCs in the atmosphere had stabilized, and CFCs are expected to disappear gradually from the atmosphere over the next century.
Bibliography
Joesten, Melvin D., John L. Hogg, and Mary E. Castellion. “Chlorofluorocarbons and the Ozone Layer.” In The World of Chemistry: Essentials. 4th ed. Belmont, Calif.: Thomson Brooks/Cole, 2007.
Newman, Michael C., and Michael A. Unger. “Environmental Contaminants.” In Fundamentals of Ecotoxicology. 2d ed. Boca Raton, Fla.: CRC Press, 2003.
Parson, Edward A. Protecting the Ozone Layer: Science and Strategy. New York: Oxford University Press, 2003.
Western, Luke N. "Global Increase of Ozone-Depleting Chlorofluorocarbons from 2010 to 2020." Nature Geoscience, vol. 16, 3 Apr. 2023, pp. 309-313, doi.org/10.1038/s41561-023-01147-w. Accessed 16 July 2024.