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Chlorofluorocarbons (CFCs) are hydrocarbons, such as freon, in which some or all of the hydrogen atoms have been replaced by fluorine atoms. CFCs can be liquids or gases, are nonflammable and heat-stable, and are used as refrigerants, aerosol propellants (such as in deodorant, whipped cream, and air fresheners), and solvents.
When released into the air, CFCs slowly rise through the Earth's lower atmosphere, and up to the stratosphere (second atmospheric layer, located about 7 to 30 miles [11 and 48 kilometers] above the Earth's surface). There they are converted by the sun's ultraviolet rays into chlorine compounds. The chlorine compounds react with stratospheric ozone molecules (O3), converting them into ordinary oxygen molecules (O2).
The release of CFCs into the atmosphere depletes the beneficial ozone layer faster than it can be recharged by natural processes. (The ozone layer is the atmospheric layer located approximately 15 to 30 miles above Earth's surface that protects the lower atmosphere from harmful radiation.) The loss of stratospheric ozone has been linked to a number of human health problems, including skin cancer, sunburns, eye cataracts, and suppression of the immune system.
In 1977, the U.S. government banned the use of all nonessential fluorocarbon aerosols, and in 1987 an international treaty banning CFCs was drafted. Chemical industries are mandated to reduce the levels of CFCs they manufacture by 50 percent by the year 2000. In addition, international treaties have restricted the manufacture and use of CFCs in other parts of the world.
Since 1988 there has been a substantial decline in the atmospheric buildup of CFCs. Experts suggest that concentrations of CFCs will peak before the year 2000, allowing the ozone layer to begin the slow process of repairing itself. However, a CFC molecule survives in the atmosphere for 50 to 100 years. And as long as CFCs persist, they will continue to destroy ozone.
Sources: Gay, Kathlyn. Ozone, pp. 50, 56-57; Hazen, Robert M., and James Trefil. Science Matters: Achieving Scientific Literacy, pp. 268-69; Science News, vol. 144 (September 11, 1993), p. 172.
The ozone layer is found from 10 to 20 miles above the earth's surface. It is composed of oxygen atoms and has a blue tint. As sun rays pelt the earth, the ozone layer absorbs part of the radiation and prohibits it from hitting the earth's surface. This protects earth's inhabitants from harmful sun damage.
CFCs are man-made chemicals that have been in production for more than a half century. These chlorine containing substances are found in refrigerant, aerosols, and solvents. Due to their long lifetimes and the fact that they do not wash away in rain, it is possible for CFCs to rise up into the ozone layer above the earth, where they eventually break down due to exposure to ultraviolet radiation. As they decompose, they release chlorine and bromine into the ozone layer. These two chemicals are responsible for damaging and depleting the ozone layer. For every one chlorine atom that is released into the ozone layer, 100,000 ozone molecules are destroyed. Thus, the CFCs cause the ozone layer to break down faster than it can replace itself. While some atmospheric chlorine may be cause by certain natural occurrences, such as large fires, volcanic eruptions and marine life, most chlorine in the ozone layer is due to CFCs and other man-made chemical
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