Tuesday, July 22, 2008

Chlorofluorocarbon (CFC)

Chlorofluorocarbon, is any of a group of synthetic organic compounds that contain chlorine, fluorine, and carbon. The two most common chlorofluorocarbons (CFC's) are trichlorofluoromethane, also called CFC-11, and dichlorodifluoromethane, or CFC-12. They are used as refrigerants in air conditioners and refrigerators and to make plastic foams for furniture and insulation.

CFC-11 and CFC-12 are nonpoisonous and nonflammable under normal conditions, and they are easily converted from liquid to gas or from gas to liquid form. These properties make the two compounds useful as propellants in aerosol spray products. However, chlorofluorocarbons (CFC's) are pollutants that destroy the ozone layer in the upper atmosphere. Scientific studies indicate that CFC's harm the environment by breaking down ozone molecules in the earth's upper atmosphere. Ozone, a form of oxygen, protects plants and animals from the harmful ultraviolet rays of the sun. It shields the earth's surface from more than 95 percent of the sun's ultraviolet radiation. As CFC's reach the upper atmosphere, they break apart and release chlorine atoms. These chlorine atoms can react chemically with the ozone and convert it to ordinary oxygen gas. As CFC's thin the ozone layer, more ultraviolet radiation reaches the surface of the earth. Overexposure to such radiation damages plants and greatly increases people's risk of skin cancer.

Since the 1970's, representatives of many nations have met to discuss ways of limiting the pollution that affects air and water. These nations have created environmental treaties to help control such problems as acid rain, the thinning of the ozone layer, and the dumping of waste into oceans. In a treaty called the Montreal Protocol on Substances That Deplete the Ozone Layer, which took effect in 1989, the major CFC-producing nations agreed to gradually stop producing the chemicals. A 1991 amendment to the treaty called for a total ban on CFC's by 2000. By 1996, most industrialized countries, including the United States, had ended production of CFC's.

In 1992, representatives of 178 nations met in Rio de Janeiro, Brazil, for the United Nations (UN) Conference on Environment and Development. This meeting, known as the Earth Summit, was one of the most important global environmental conferences ever held. The UN members signed agreements on the prevention of global warming, the preservation of forests and endangered species, and other issues.

In 1978, the United States government banned chlorofluorocarbon aerosols for most uses. In 1988, the Du Pont Company, the world's largest producer of CFC's, announced plans to phase out production of these chemicals. Du Pont sold CFC's under the registered trademark Freon. The United States and most other industrialized countries that produced CFC's agreed in 1990 to end production by 2000. There are two exceptions to the ban in the United States: (1) use as a propellant in inhalers for asthma patients, and (2) use in the manufacture of methyl chloroform to clean O-ring seals for the space shuttle. In late 1992, the industrialized countries agreed to move the deadline to the end of 1995. By 1996, most of these countries had complied with this deadline. Other countries planned to end production by 2010.

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