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An environmental legacy of the twentieth century is the use of gaseous compounds called chlorofluorocarbons (CFCs, which are also known as Freon) in a variety of household and personal products. The escape of these compounds into the atmosphere has triggered the destruction of an atmospheric gas called ozone.

The lessened ozone has led to an increase in the amount of cell damaging ultraviolet (UV) light reaching Earth’s surface. The increasing prevalence of skin ailments, including some cancers, has been linked to the increased amount of UV light.

Beginning in the 1980s, the decrease in atmospheric ozone spurred international efforts to phase out the use of CFCs. The best-known example of this international resolve is the Montreal Protocol on Substances that Deplete the Ozone Layer, a treaty signed by 191 nations that took effect in 1989. The treaty, which has since been revised seven times, has established a timetable for phasing-out the use of several ozone-destroying compounds including CFCs.

Historical Background and Scientific Foundations

The five main chemical formulations of CFCs that were developed in the 1930s proved to be popular in a variety of manufactured products since they were non-toxic, non-poisonous, non-flammable, and not prone to react with other compounds. Almost immediately, CFCs began to be used as a replacement for harmful compounds such as ammonia. Uses included application as a refrigeration coolant, cleaning solvent (particularly in electronic industry in cleaners for circuit boards), and as a propellant in spray cans and foam-emitting fire extinguishers.

Over the next three decades, CFCs that were given off by the various products dissipated into the atmosphere. Until 1973, if an accumulation of CFCs in the atmosphere was thought of at all, it was dismissed as inconsequential. Then, scientists at the University of California, Irvine, discovered that CFCs persist for 20 to 100 years in the region of the atmosphere known as the stratosphere. They also proposed that this longevity could have adverse effects on the ozone constituent of the atmosphere.

Subsequently, their view was confirmed. It was shown that the UV portion of the incoming sunlight can break the CFC molecule apart. The UV cleavage releases chlorine, and the free chlorine destroys ozone. Another type of hydrocarbon that contains bromine instead of chlorine is also destructive to ozone.

Ozone is made up of three oxygen atoms. Its chemistry makes intact ozone capable of absorbing UV radiation, which reduces the amount of this portion of sunlight that reaches Earth’s surface. However, with the depletion of ozone from the stratosphere, the levels of UV radiation penetrating to the ground increased during the latter half of the twentieth century.

The reason that this is a concern is because UV light is very energetic. The energy allows the light to penetrate into the top layers of skin and through the cells in these layers. The cells can be damaged on prolonged exposure to the sun. One example of the damage that can be caused is sunburn. More serious damage can result, since the energy in UV light is sufficient to break one or both of the strands of the double helix of genetic material (usually deoxyribonucleic acid, DNA) that is present inside most plant, animal, and human cells. Sometimes the damage can be repaired. However, sometimes this repair is not accomplished correctly. Alternately, the breakage of the genetic material can be too extensive to be completely fixed. The result can be a change (mutation) in the cells that survive. Although some changes are not serious, others are. For example, some mutations affect the genetic checks and balances that control the ability of cells to grow and divide. A consequence of this breakdown in normal cell processes can be uncontrolled growth and division of cells. Such cells are cancerous. Increased exposure to UV light has been linked with the increasing prevalence of several types of cancer.

Furthermore, the long lifetime of CFCs means that even a free chlorine from one CFC compound can destroy ozone for decades.

Concern over ozone depletion and the link between this depletion and the increased threat to health became urgent in the early 1980s when it was discovered that the atmosphere over Antarctica contained much less ozone than other regions. Satellite images of the near-depletion of Antarctic ozone—a phenomenon dubbed the ozone hole—galvanized the global community to take action to curb the release of CFCs into the atmosphere.

Impacts and Issues

Following the widespread adoption of the Montreal Protocol, use of CFCs has declined. For example, in 1983 the global production of CFCs was more than 1.2 million tons. By 2004 global production had declined to 70,000 tons.


ATMOSPHERE: The air surrounding Earth, described as a series of layers of different characteristics. The atmosphere, composed mainly of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases, acts as a buffer between Earth and the sun.

OZONE: An almost colorless, gaseous form of oxygen, with an odor similar to weak chlorine, that is produced when an electric spark or ultraviolet light is passed through air or oxygen.

PRIMARY POLLUTANT: Any pollutant released directly from a source to the atmosphere.

RADIOSONDES: Set of instruments carried into the atmosphere by weather balloons to measure temperature, humidity, and air pressure at various altitudes.

There have been some notable examples of success. Beginning in January 2008, for example, the country of Indonesia has banned the importation of CFCs, two years ahead of the deadline established under the Montreal Protocol.

Emissions of CFCs from developed countries including the United States have essentially stopped,

since CFC-containing products are no longer sold. However, production of CFCs is continuing in other countries, and CFC-containing products continue to be sold and used in some developing and underdeveloped countries. So, although the amount of CFCs entering the atmosphere has dropped, release continues.

Combined with the atmospheric persistence of CFCs, the release will continue to result in ozone destruction. Even if the release of CFCs could be totally stopped now, ozone destruction would continue for almost a century.

Hydrofluorocarbons (HFCs) have been implemented as replacements for CFCs. HFCs still contain ozone-destructive chlorine atoms. But, the presence of hydrogen makes HFCs reactive with compounds in the troposphere, a region of the atmosphere that is closer to Earth’s surface than the ozone-rich stratosphere. This reduces the chances that HFCs will reach the stratosphere and destroy ozone.

Hydrofluorocarbons (HFCs) do not contain chlorine, and so do not affect ozone levels. However, as of 2008, no implementation targets have been set for HFCs.

See Also Greenhouse Gases; Montreal Protocol; Ozone Hole



DiMento, Joseph F. C., and Pamela M. Doughman. Climate Change: What It Means for Us, Our Children, and Our Grandchildren. Boston: MIT Press, 2007.

Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. New York: Rodale Books, 2006.

Seinfeld, John H., and Spyros N. Pandis. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. New York: Wiley Interscience, 2006.

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Chlorofluorocarbons (CFCs) are a class of chemicals that contain only atoms of carbon, chlorine, and fluorine. As a group, they are unreactive, stable, and poorly soluble in water. Commercially, the most important CFCs were derivatives of methane and ethane. These included trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) and 1,2-dichloro-1,1,2,2-tetrafluoroethane (CFC-114). CFCs were first introduced in the 1930s as safe replacements for refrigerants such as sulfur dioxide, ammonia, chloroform, and carbon tetrachloride. During World War II they were used to produce aerosols of insecticides. During the next fifty years the applications expanded to include foam blowing, precision cleaning, air conditioning, refrigeration, and propellants for medicinal, cosmetic, food, and general-purpose aerosols. These uses eventually resulted in large emissions of CFCs into the atmosphere. Because of their low chemical reactivity, CFCs typically have long atmospheric residence times, and as a consequence are distributed globally.

In 1974, M. Molina and F. Rowland hypothesized that when CFCs reached the stratosphere they would break down to release chlorine atoms. The chlorine atoms would then react with stratospheric ozone, breaking it down into oxygen. Since stratospheric ozone absorbs much of the sun's ultraviolet radiation, decreased stratospherel ozone levels could lead to increased ground-level ultraviolet radiation. This could adversely affect crop growth, and also lead to increases in cataracts and nonmelanoma skin cancer. Following reports of a marked drop in "column ozone" over Antarctica (the "ozone hole") during the Antarctic winter of 1986, most of the nations of the world drafted and signed an agreement calling for the phaseout of CFCs. This agreement is known as the Montreal Protocol. Included were all CFCs and bromochlorofluorocarbons (halons), which are used in fire suppression systems.

The banning of CFCs has lead to research to identify other chemicals that can be used in the same applications but without the same environmental concerns. Two classes of chemicals that have been identified are the hydrochlorofluorocarbons (HCFCs) and the hydrofluorocarbons (HFCs). The presence of hydrogen in the molecule promotes attack by hydroxyl radicals in the atmosphere leading to more rapid breakdown and shorter atmospheric lifetimes. While HFCs do not contain chlorine and therefore can not contribute to ozone depletion, HCFCs do contain chlorine and can contribute to ozone depletion. However, due to the presence of hydrogen, their atmospheric lifetimes are much shorter than the CFCs and the corresponding ozone depletion values are smaller, typically by a factor of between 10 and 100. In subsequent amendments to the Montreal Protocol, the HCFCs have been classified as transitional substances and they are also scheduled for a phase-out, but at much later dates.

One of the reasons the CFCs have been used so extensively and in such a wide variety of applications is their low level of toxicity. The acute, median lethal concentration for a four-hour exposure to many of these materials is greater than 50,000 parts per million (ppm) (5% in the air). In longer term exposure studies, rarely are effects seen below 20,000 ppm (2% in the air). The one exception to this is the potential of all of these compounds, as well as hydrochlorocarbons and hydrocarbons, to sensitize the heart to the action of adrenaline. In the 1960s, it was first reported that teenagers were abusively inhaling CFCs to get a preanesthectic "high." However, in some cases, the individual would get excited, run around and then die, with no apparent cause of death. Subsequent research demonstrated that this effect could be reproduced in laboratory animals which are now used to test possible CFC replacements.

George M. Rusch

(see also: Ambient Air Quality [Air Pollution]; Atmosphere; Hazardous Air Pollutants; Melanoma; Skin Cancer; Ultraviolet Radiation )


Lashof, D. A., and Ahuja, D. R. (1990). "Relative Contributions of Greenhouse Gas Emissions to Global Warming." Nature 344:529531.

Molina, M. J., and Rowland, F. S. (1974). "Stratospheric Sink for Chlorofluoromethanes: Chlorine Atom Catalyzed Destruction of Ozone." Nature 249:810812.

National Aeronautics and Space Administration (NASA) (1986). Present State of Knowledge of the Upper Atmosphere: An Assessment Report. Ref. Publ. No. 1162. Washington, DC: Author.

Reinhardt, C. F.; Mullin, L. S.; and Maxwell, M. E. (1973). "Epinephrine-Induced Cardiac Arrhythmia Potential of Some Common Industrial Solvents." Journal of Occupational Medicine 15 (12):953955.

World Meteorological Organization (1999). 19981999 WMO Global Ozone Research and Monitoring Project. Geneva: Author.

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Chlorofluorocarbon (CFC)

A chlorofluorocarbon (CFC) is an organic compound typically consisting of chlorine, fluorine, carbon , and hydrogen. Freon, a trade name, is often used to refer to CFCs, which were invented in the 1930s and have been used widely as aerosol propellants, refrigerants, and solvents. Odorless, colorless, nontoxic, and nonflammable, CFCs are considered valuable industrial products and have proven an especially safe and reliable aid in food preservation. However, the accumulation of CFCs in the stratosphere that may be linked to ozone depletion has generated considerable public debate and has led to legislation and international agreements (such as the Montreal Protocol and its amendments, signed by 148 countries) that banned the production of most CFCs by the year 2000. One of the substitutes developed by industry, the hydrochlorofluorocarbons (HCFCs), still contain enough chlorine to interfere with atmospheric ozone chemistry , although in much lesser amounts than CFCs. The Copenhagen amendment to the Montreal Protocol calls for the cessation of HCFC production by 2030. Hydrofluorocarbons (HFCs) are currently considered a safer substitute due to prevent ozone loss due to their lack of chlorine and shorter reactive time. As of 2002, new automobiles in the United States contain HFC refrigerant products in the air conditioners.

In the late 1920s, researchers had been trying to develop a coolant that was both nontoxic and nonflammable. At that time, methyl chloride was used, but if it leaked from the refrigerator, it could explode. This danger was demonstrated in one case when methyl chloride gas escaped, causing a disastrous explosion in a Cleveland hospital. Sulfur dioxide was sometimes used as an alternative coolant because its unpleasant odor could be easily noticed in the event of a leak. The problem was brought to the attention of Thomas Midgley Jr., a mechanical engineer at the research laboratory of General Motors. He was asked by his superiors to try to manufacture a safe, workable coolant. (At that time, General Motors was the parent company to Frigidaire.) Midgley and his associate chemists thought that fluorine might work because they had read that carbon tetrafluoride had a boiling point of 5°F (15°C). The compound, as it turns out, had accidentally been referenced. Its actual boiling point is 198°F (92.2°C), not nearly the level necessary to produce refrigeration. Nevertheless, the incident proved useful because it prompted Midgley to look at other carbon compounds containing both fluorine and chlorine. Within three days, Midgley's team discovered the right mix: dichlorodifluoromethane, a compound whose molecules contain one carbon, two chlorine, and two fluorine atoms. It is now referred to as CFC-12 or F-12 and was marketed as Freonas were a number of other compounds, including trichlorofluoromethane, dichlorotetrafluoroethane, and chlorodifluoromethane.

Midgley and his colleagues had been correct in guessing that CFCs would have the desired thermal properties and boiling points to serve as refrigerant gases. Because they remained unreactive, and therefore safe, CFCs were seen as ideal for many applications. Through the 1960s, the widespread manufacture of CFCs allowed for accelerated production of refrigerators and air conditioners. Other applications for CFCs were discovered as well, including their use as blowing agents in polystyrene foam. Despite their popularity, CFCs became the target of growing environmental concern by certain groups of researchers. In 1972, two scientists from the University of California, F. Sherwood Rowland and Mario Jose Molino, conducted tests to determine if the persistent characteristics of CFCs could pose a problem by remaining indefinitely in the atmosphere. Soon after, their tests confirmed that CFCs do indeed persist until they gradually ascend into the stratosphere, break down due to ultraviolet radiation, and release chlorine, which in turn affects ozone production. Their discovery set the stage for vehement public debate about the continued use of CFCs. By the mid-1970s, the United States government banned the use of CFCs as aerosol propellants but it resisted a total ban for all industries. Instead, countries and industries began negotiating the process of phasing out CFCs. As CFC use is allowed in fewer and fewer applications, a black market has been growing for the chemical. In 1997, the United States Environmental Protection Agency and Customs Service, along with other governmental agencies, initiated enforcement actions to prevent (CFC) smuggling in the United States.

See also Atmospheric pollution; Global warming; Greenhouse gases and greenhouse effect; Ozone layer and hole dynamics; Ozone layer depletion

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The chlorofluorocarbons (CFCs) are a family of organic compounds containing carbon , hydrogen (usually), and either chlorine or fluorine, or both. The members of this family can be produced by replacing one or more hydrogen atoms in hydrocarbons with a chlorine or fluorine atom. In the simplest possible case, treating methane (CH4) with chlorine yields chloromethane, CH3Cl. Treating this product with fluorine causes the replacement of a second hydrogen atom with a fluorine atom, producing chlorofluoromethane, CH2ClF.

This process can be continued until all hydrogen atoms have been replaced by chlorine and/or fluorine atoms. By using larger hydrocarbons, an even greater variety of CFCs can be produced. The compound known as CFC-113, for example, is made from ethane (C2H6) and has the formula C2F3Cl3.

Over the last three decades, the CFCs have become widely popular for a number of commercial applications. These applications fall into four general categories: refrigerants, cleaning fluids, propellants , and blowing agents. As refrigerants, CFCs have largely replaced more harmful gases such as ammonia and sulfur dioxide in refrigerators, freezers, and air conditioning systems. Their primary application as cleaning fluids has been in the computer manufacturing business where they are used to clean circuit boards. CFCs are used as propellants in hair sprays, deodorants, spray paints, and other types of sprays. As blowing agents, CFCs are used in the manufacture of fast-food take-out boxes and similar containers. By the early 1990s, CFCs had become so popular that their production was a multi-billion dollar business worldwide.

For many years, little concern was expressed about the environmental hazards of CFCs. The very qualities that made them desirable for commercial applicationstheir stability , for exampleappeared to make them environmentally benign.

However, by the mid-1970s, the error in that view became apparent. Scientists began to find that CFCs in the stratosphere decomposed by sunlight. One product of that decomposition , atomic chlorine, reacts with ozone (O3) to form ordinary oxygen (O2). The apparently harmless CFCs turned out, instead, to be a major factor in the loss of ozone from the stratosphere.

By the time this discovery was made, levels of CFCs in the stratosphere were escalating rapidly. The concentration of these compounds climbed from 0.8 part per billion in 1950 and 1.0 part per billion in 1970 to 3.5 parts per billion in 1987.

A turning point in the CFC story came in the mid-1980s when scientists found that a large hole in the ozone layer was opening up over the Antarctic each year. This discovery spurred world leaders to act on the problem of CFC production. In 1987, about 40 nations met in Montreal to draft a treaty that will reduce the production of CFCs worldwide.

This action is encouraging, but it hardly solves the CFC problem. These compounds remain in the atmosphere for long periods of time (about 77 years for CFC-11 and 139 years for CFC-12), so they will continue to pose a threat to the ozone layer for many decades to come.

[David E. Newton ]



Selinger, B. Chemistry in the Marketplace. 4th ed. Sydney: Harcourt Brace Jovanovich Publishers, 1989.


O'Sullivan, D. A. "International Gathering Plans Way to Safeguard Atmospheric Ozone." Chemical & Engineering News (26 June 1989): 33-36.

Zurer, P. S. "Producers Grapple with Realities of CFC Phaseout." Chemical & Engineering News (24 July 1989): 7-13.

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chlorofluorocarbons (klōr´əflŏŏr´əkär´bənz, klôr´–) (CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. CFCs are highly effective refrigerants that were developed in response to the pressing need to eliminate toxic and flammable substances, such as sulfur dioxide and ammonia, in refrigeration units and air conditioners. The most common commercial CFCs, marketed under the trade name Freon, are trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12). Commercial CFCs are nonflammable, noncorrosive, nontoxic, and odorless, and their vapor pressures and heats of vaporization made them very suitable for refrigeration applications. They were also widely used as aerosol propellants, cleansing agents for electrical and electronic components, and foaming agents in shipping-plastics manufacturing.

In the mid-1970s, scientists at the Univ. of California, Irvine predicted that CFCs could cause ozone depletion in the upper atmosphere; this was later confirmed by ground-based and satellite studies. When CFCs are released into the atmosphere, they move via air currents to altitudes ranging from 15 to 25 mi (25–40 km). There, they are dissociated by ultraviolet light as given by the reaction: CF2Cl2 → CF2Cl + Cl. The resulting free chlorine atoms (Cl) decompose ozone (O3) into oxygen (O2), Cl + O3 → ClO + O2, and are regenerated by interaction with free oxygen atoms (O), ClO + O → Cl + O2. When chlorine is regenerated, it is free to continue to break down other ozone molecules. This process continues for the atmospheric lifetime of the chlorine atom (one to two years), during which it destroys an average of 100,000 ozone molecules. Chlorine radicals are removed from the stratosphere after forming two compounds that are relatively resistant to dissociation by ultraviolet light: hydrogen chloride (HCl) and chlorine nitrate (ClONO2). Dissociation is slow enough so that these compounds can diffuse down to the troposphere, where they react with water vapor and are removed in rain.

Bromine radicals react like chlorine radicals to remove ozone from the stratosphere and sometimes react in concert with chlorine. Bromine is much more destructive than chlorine because the compounds hydrogen bromide (HBr) and bromine nitrate (BrONO2) are much more susceptible to dissociation by ultraviolet light; thus, many more ozone molecules are destroyed before the bromine molecules can diffuse downward. Fluorine radicals combine to form hydrogen fluoride (HF) and other stable compounds that do not affect the ozone layer.

Ozone is vital to human and animal survival because it is responsible for the absorption of the sun's ultraviolet light. Without this protection, blindness and skin cancers could result from penetrating ultraviolet light. In 1987 an international treaty, the Montreal Protocol, called for reducing CFC use by 50% by 2000. A 1992 amendment to the treaty called for the end of CFC production in industrial countries by 1996, and by 1993 CFC emissions had dropped dramatically.

Halons are organic compounds that are similar to CFCs. They contain carbon, fluorine, and bromine and may contain chlorine. Halons have been used primarily as propellants in fire extinguishers. Because of their bromine content they are even more destructive to ozone than CFCs, and an amendment to the Montreal Protocol banned their use by 1994.

Hydrochlorofluorocarbons (HCFCs) are organic compounds that are similar to CFCs but less destructive to ozone. HCFCs consist of carbon, hydrogen, chlorine and fluorine. They are used as replacements for CFCs, but are to be phased out by the year 2020, as specified by the Montreal Protocol as amended, when they are expected to be replaced by hydrofluorocarbons (HFCs). HFCs are organic compounds that contain hydrogen, carbon and fluorine. HFCs, which do not contain chlorine, do not have any potential for the destruction of ozone, and so are suitable replacements for CFCs.

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chlorofluorocarbonBrian, cyan, Gaian, Geminian, Hawaiian, ion, iron, Ixion, lion, Lyon, Mayan, Narayan, O'Brien, Orion, Paraguayan, prion, Ryan, scion, Uruguayan, Zion •andiron •gridiron, midiron •dandelion • anion • Bruneian •cation, flatiron •gowan, Palawan, rowen •anthozoan, bryozoan, Goan, hydrozoan, Minoan, protozoan, protozoon, rowan, Samoan, spermatozoon •Ohioan • Chicagoan • Virgoan •Idahoan •doyen, Illinoisan, IroquoianEwan, Labuan, McEwan, McLuhan, Siouan •Saskatchewan • Papuan • Paduan •Nicaraguan • gargantuan •carbon, chlorofluorocarbon, graben, hydrocarbon, Laban, radiocarbon •ebon • Melbourne • Theban •gibbon, ribbon •Brisbane, Lisbon •Tyburn •auburn, Bourbon •Alban • Manitoban • Cuban •stubborn •Durban, exurban, suburban, turban, urban

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chlorofluorocarbon (CFC) Chemical compound in which hydrogen atoms of a hydrocarbon, such as an alkane, are replaced by atoms of fluorine, chlorine, carbon and sometimes bromine. CFCs are inert, stable at high temperatures and are odourless, colourless, nontoxic, noncorrosive and nonflammable. Under the trade name of Freons, CFCs were widely used in aerosols, fire-extinguishers, refrigerators, and in the manufacture of foam plastics. The two most common are Freon 11 (trichlorofluoromethane, CFCl3) and Freon 12 (dichlorodifluoromethane, CF2Cl2). CFCs slowly drift into the stratosphere and are broken down by the Sun's ultraviolet radiation into chlorine atoms that destroy the ozone layer. It often takes more than 100 years for CFCs to disappear from the atmosphere. Growing environmental concern led to an international agreement in 1990 to reduce and eventually phase out the use of CFCs, and to develop safe substitutes.

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chlorofluorocarbon (CFC) One of a range of chemically inert compounds in which a chlorinated hydrocarbon is treated with hydrogen fluoride (e.g. CFC-12 is CCl2F2, CFC-21 is CHCl2F). CFCs have been used widely in fire extinguishers and as solvents, refrigerants, aerosol propellants, and in the manufacture of foam plastics. Their use is being phased out because of their capacity for absorbing long-wave electromagnetic radiation (i.e. they are ‘greenhouse’ gases) and because their chemical stability allows them to survive in the atmosphere long enough to enter the stratosphere, where they are decomposed by ultraviolet radiation, liberating chlorine that is implicated in the thinning of the ozone layer.

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chlorofluorocarbons (CFCs) Compounds obtained by replacing the hydrogen atoms of hydrocarbons by chlorine and fluorine atoms. Their high stability to temperature makes them suitable for a variety of uses, including aerosol propellants, oils, polymers, etc. They are often known as freons. Their widespread use in aerosols and refrigerator coolants has led to increased concentrations in the upper atmosphere, where photochemical reactions cause them to break down and react with ozone, which results in depletion of the ozone layer. For this reason CFCs are now being replaced with less damaging alternatives. See also pollution.

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chlo·ro·fluor·o·car·bon / ˌklôrōˌfloŏrōˈkärbən/ (abbr.: CFC) • n. any of a class of compounds of carbon, hydrogen, chlorine, and fluorine, typically gases used chiefly in refrigerants and aerosol propellants. They are harmful to the ozone layer in the earth's atmosphere.