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CFCs
Chlorofluorocarbons (CFCs) are a
family of chemical compounds developed back in the 1930's as safe, non-toxic,
non-flammable alternative to dangerous substances like ammonia for purposes of
refrigeration and spray can propellants. Their usage grew enormously over the
years. One of the elements that make up CFCs is chlorine. Very little chlorine
exists naturally in the atmosphere. But it turns out that CFCs are an excellent
way of introducing chlorine into the ozone layer. The ultraviolet radiation at
this altitude breaks down CFCs, freeing the chlorine. Under the proper
conditions, this chlorine has the potential to destroy large amounts of ozone.
This has indeed been observed, especially over Antarctica. As a consequence,
levels of genetically harmful ultraviolet radiation have increased.
U.
S. Food and Drug Administration Graphic
Chlorofluorocarbons (CFCs) are highly stable compounds
that are used as propellents in spray cans and in refrigeration units. They are
several organic compounds composed of carbon, fluorine, chlorine, and hydrogen.
CFCs are manufactured under the trade name Freon (q.v.).
Developed during the 1930s, CFCs found wide application
after World War II. These halogenated hydrocarbons, notably
trichlorofluoromethane (CFC-11, or F-11) and dichlorodifluoromethane (CFC-12, or
F-12), have been used extensively as aerosol-spray propellants, refrigerants,
solvents, and foam-blowing agents. They are well-suited for these and other
applications because they are nontoxic and nonflammable and can be readily
converted from a liquid to a gas and vice versa.
Chlorofluorocarbons or CFCs (also known as Freon) are
non-toxic, non-flammable and non-carcinogenic. They contain fluorine atoms,
carbon atoms and chlorine atoms. The 5 main CFCs include CFC-11 (trichlorofluoromethane
- CFCl3), CFC-12 (dichloro-difluoromethane - CF2Cl2), CFC-113 (trichloro-trifluoroethane
- C2F3Cl3), CFC-114 (dichloro-tetrfluoroethane - C2F4Cl2), and CFC-115 (chloropentafluoroethane
- C2F5Cl).
CFCs have been found to pose a serious environmental
threat. Studies undertaken by various scientists during the 1970s revealed that
CFCs released into the atmosphere accumulate in the stratosphere, where they had
a deleterious effect on the ozone layer. Stratospheric ozone shields living
organisms on Earth from the harmful effects of the Sun's ultraviolet radiation;
even a relatively small decrease in the stratospheric ozone concentration can
result in an increased incidence of skin cancer in humans and in genetic damage
in many organisms. In the stratosphere the CFC molecules break down by the
action of solar ultraviolet radiation and release their constituent chlorine
atoms. These then react with the ozone molecules, resulting in their removal.
CFCs have a lifetime in the atmosphere of about
20 to 100 years, and consequently one free chlorine atom from a CFC molecule can
do a lot of damage, destroying ozone molecules for a long time. Although
emissions of CFCs around the developed world have largely ceased due to
international control agreements, the damage to the stratospheric ozone layer
will continue well into the 21st century.
The rise in
effective stratospheric chlorine values in the 20th century has slowed and
reversed in the last decade . Effective stratospheric chlorine values are a
measure of the potential for ozone depletion in the stratosphere, obtained by
summing over adjusted amounts of all chlorine and bromine gases. Effective
stratospheric chlorine levels as shown here for midlatitudes will return to 1980
values around 2050. The return to 1980 values will occur around 2065 in polar
regions. In 1980, ozone was not significantly depleted by the chlorine and
bromine then present in the stratosphere. A decrease in effective stratospheric
chlorine abundance follows reductions in emissions of individual halogen source
gases. Overall emissions and atmospheric concentrations have decreased and will
continue to decrease given international compliance with the Montreal Protocol
provisions. The changes in the atmospheric abundance of individual gases at
Earth’s surface shown in the panels were obtained using a combination of
direct atmospheric measurements, estimates of historical abundance, and future
projections of abundance. The past increases of CFCs, along with those of CCl4
and CH3CCl3, have slowed significantly and most have reversed in the last
decade. HCFCs, which are used as CFC substitutes, will continue to increase in
the coming decades. Some halon abundances will also continue to grow in the
future while current halon reserves are depleted. Smaller relative decreases are
expected for CH3Br in response to production and use restrictions because it has
substantial natural sources. CH3Cl has large natural sources and is not
regulated under the Montreal Protocol.
World Production
of CFCs 
Thousands
Of Tons
| 1986 |
| 1987 |
| 1988 |
| 1989 |
| 1990 |
| 1991 |
| 1992 |
| 1993 |
| 1994 |
| 1995 |
| 1996 |
| 1997 |
| 1998 |
| 1999 |
| 2000 |
| 2001 |
| 2002 |
| 2003 |
| 2004 |
|
| 1174 |
| 1250 |
| 1260 |
| 1120 |
| 822 |
| 719 |
| 634 |
| 532 |
| 346 |
| 258 |
| 156 |
| 163 |
| 150 |
| 148 |
| 133 |
| 101 |
| 94 |
| 83 |
| 70 |
|
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