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Mesosphere - a layer of atmosphere extending from the top of the stratosphere to an altitude of about 55 miles.
Stratosphere - an upper portion of the atmosphere above 17 km, more or less, depending on latitude, season, and weather, and is roughly 33 km in width, ozone layer located here and is approximately 25 km from the earth's surface.
Troposphere - extends outward from the earth's surface 17 km. Temperature generally decreases with altitude and clouds form.
Chlorofluorocarbons (CFCs) or freons were discovered in the 1930s. They're compounds made of chlorine, fluorine and carbon and are nonreactive, nontoxic, noncaustic, noncorrosive and nonflammable. These properties make CFCs ideal for use as:
- coolants in refrigerators and air conditioners (1);
- propellants in aerosol sprays;
- plastic foam blowing agents (used in making, for example, Styrofoam); and
- cleaning solvents used in the electronics industry.
However, in 1974 scientists discovered that the same qualities of stability that make CFCs desirable for so many uses can result in major environmental problems when these gases drift unaltered into the stratosphere.
The stratosphere contains a thin layer of a pale blue, poisonous gas called ozone and is commonly known as the ozone layer. Ozone forms when oxygen molecules interact with ultraviolet rays from the sun. Under normal circumstances, part of the ozone layer is continuously being depleted and regenerated. For this reason, the layer varies in thickness. The ozone layer is an important protective screen for life on earth, filtering out more than 99 percent of the ultraviolet rays before they can reach the ground.
When CFCs are allowed to escape into the atmosphere, they rise until they reach the stratosphere where ultraviolet light breaks them down into chlorine and other chemicals. The chlorine atom (Cl) released in this process then reacts with an ozone molecule (O3). An atmospheric oxygen molecule (O2) and a molecule of chlorine monoxide (ClO) are formed in the process. ClO is relatively unstable and will react with any free oxygen atoms (O) to form O2 and a free chlorine atom . The chlorine atom then reacts with another ozone molecule. One chlorine atom has the potential to destroy 10,000 or more molecules of ozone before it returns to the troposphere. As more and more of the ozone is depleted, the ozone layer gets thinner and lets more of the sun's ultraviolet rays reach the earth's surface. In 1985, British scientists reported that there is a hole about the size of the United States in the ozone layer over Antarctica. By 1987, scientists from four other countries concluded that the "hole" was caused by CFCs.
Too much ultraviolet radiation can cause skin cancer, immune deficiencies, and cataracts. In 1987, the Environmental Protection Agency (EPA) estimated that with a 5 percent increase in CFCs per year, 40 million additional Americans will get cancer over the next 88 years and of those, 800,000 will die. Damage to the ozone layer by CFCs reduce crop yields. Terrestrial and aquatic ecosystems are also harmed. In addition, CFCs are responsible for 10-20 percent of the greenhouse effect. Chlorine monoxide produced when CFCs react with ozone, traps solar radiation the same way other carbon gases do, contributing to the warming of the troposphere.
One of the major problems in addressing this issue is the dilemma of environmental protection versus economics. The CFC-manufacturing industry in the United States was valued at more than $28 billion dollars in 1986. That same year, it was estimated that more then 780,000 American jobs were related in some way to the use of CFCs. To further complicate the situation, research has shown that the synthetic chemicals used in producing CFCs are extremely energy efficient and relatively safe for the worker and consumer. To combat the growing problem with CFCs worldwide, the United States, Canada and some European countries banned nonessential use of CFCs, such as propellants or aerosols used in spray cans, in 1978. In 1987, 31 countries met in Montreal and signed the Montreal Protocol, which requires countries to cut CFC usage in half by 1999. By 1989, 66 countries had signed the Protocol. Since the Protocol was first signed, major advancements in CFC-alternative technology for use in food packaging and solvents have been announced. The 1990 US Clean Air Act Amendments include a provision to phase out CFCs by the year 2000. But even if all use of CFCs was halted today, the CFCs already released into the atmosphere will continue to break down for decades to come and continue to deplete the ozone layer.(1) To receive the following documents, contact the Office of Air and Radiation, US Environmental Protection Agency, 401 M Street, SW, Washington, DC 20460.
- Disposing of Appliances with Refrigerants: What you should know.
- EPA/430/F-93/003, May 1993
- Refrigerant Recycling in Motor Vehicle Air Conditioners
- EPA/400/K-92/003, Sept. 1992