"Use of these results may help evaluate changes in the atmospheric concentrations of CFC-11 in the future," he said. "They add to the understanding of a very important source of CFCs."

Chlorine contained in CFCs damages the earth's ozone layer, a thin shield of oxygen that protects the planet from ultraviolet radiation. A single chlorine atom — contained in CFCs and also found naturally — can destroy more than 100,000 ozone molecules, although ozone can be reformed over time by a chemical reaction stimulated by sunlight. The upper part of the atmosphere known as the stratosphere contains approximately 3 billion kilograms of ozone — enough to create a layer about an eighth of an inch thick that circles the globe.

Depletion of the ozone layer leads to higher levels of a certain type of ultraviolet (UV) radiation reaching the earth's surface. Previous testing has shown that higher UV-B levels increase the risk of skin cancer, harm plant life, reduce the population of sea life and contribute to the increase of carbon dioxide and other greenhouse gases believed to be responsible for atmospheric warming, according to the U.S. Environmental Protection Agency.

Because of the dangers of exhausting the ozone layer, more than 120 countries signed the 1987 "Montreal Protocol" to control CFC emissions. After 1995, when production of most CFCs stopped, they ceased being used in aerosol cans and in the coolant known as Freon. New products, including refrigerators, use substitutes with similar properties. Additional amounts of CFC-11 can be found in air conditioners, insulation and some industrial appliances. A different type of CFC is used in the product marketed as Styrofoam.

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Contact: Beverly Hassell
b_hassell@acs.org
202-872-4065
American Chemical Society
17-Jun-2001