EJWIRQNMBNTAL
INBIC&TOES
Protection of the Ozone Layer
Over 60 years ago, chlorofluorocarbons (CFCs) were invented in
the United States, and they soon found many uses throughout
the world in refrigeration, air conditioning, and other industrial
processes. Due to scientific evidence that CFCs and other chemicals
destroy ozone in the upper atmosphere, the United States, the
country which has traditionally been the largest emitter of CFCs
worldwide, is rapidly scaling back the use of these chemicals and
phasing out their production.
The ozone (Os) layer in the stratosphere protects life on earth from
exposure to dangerous levels of ultraviolet light. It does so by filtering
out harmful ultraviolet radiation from the sun. When CFCs and other
"Indicator,* ,
U.S. Impact
*on "the* Ozone
Layer
1958 1962
m cFc-11
1966 1970
H CFC-12
1974 1978 1982
HCFC-22 D CFC-113
1986 1990
B GH3CCI3
United States iiwfranmental
Office of Policy, Planning
-° and Evaluation
Office of Air and ftsdiiftifn
World Resources"
Institute
199S
ozone-degrading chemicals are emitted, they mix with the atmosphere
and eventually rise to the stratosphere. There, the chlorine and the
bromine they contain catalyze the destruction of ozone. This
destruction is occurring at a more rapid rate than ozone can be created
through natural processes.
The degradation of the ozone layer leads to higher levels of
ultraviolet radiation reaching Earth's surface. This in turn can lead to a
greater incidence of skin cancer, cataracts, and impaired immune
systems, and is expected also to reduce crop yields, diminish the
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productivity of the oceans, and possibly to contribute to
the decline of amphibious populations that is occurring
around the world.
The chemicals most responsible for the destruction of
the ozone layer are chlorofluorocarbons, carbon
tetrachloride, methyl bromide, methyl chloroform, and
halons. Chlorofluorocarbons have long been widely used as
coolants in refrigerators and air conditioners and as
foaming agents, solvents, and aerosol propellants. Carbon
tetrachloride and methyl chloroform are important
industrial solvents. In the United States, carbon
tetrachloride is now used almost entirely as a feedstock for
the production of chlorofluorocarbons. Halogenated CFCs
(HCFCs) have many of the same uses as CFCs and are
increasingly employed as interim substitutes for CFCs.
Halons have been used in fire extinguishers.
Long predicted, the degradation of the ozone layer was
dramatically confirmed when a large hole in the layer over
Antarctica was reported in 1985. Smaller but significant
stratospheric decreases have been seen over more
populated regions of the Earth. Subsequent research
established that industrial chemicals are responsible for the
observed depletions of ozone over Antarctica and play'a
major role in global ozone losses.
HUMAN
ACTIVITIES
Chlorine and bromine are emitted to the atmosphere from
both natural and human sources. These very stable
human-made chemicals are not soluble in water and are
not broken down chemically in the lower atmosphere.
Thus they survive long enough to reach the stratosphere.
The CFCs and carbon tetrachloride are relatively
unreactive in the lower atmosphere (the troposphere) and
move unscathed into the stratosphere where they are
decomposed by intense sunlight, releasing chlorine to
catalyze the destruction of ozone molecules. Certain
ozone-depleting chemicals (HCFC-22 and methyl
chloroform) are more reactive in the troposphere and
deliver less of their initial chlorine load to the
stratosphere. Halons also are generally reactive in the
troposphere and'deliver only a fraction of their initial load
of bromine to the stratosphere, but bromine is 40 times
more efficient at destroying ozone than chlorine.
Increasing attention is being focused on the
ozone-depleting role of methyl bromide, which has three
potentially major human sources (soil fumigation, biomass
burning, and the exhaust of automobiles using leaded
gasoline), in addition to a natural oceanic source.
U.S. production of ozone-depleting gases has declined
significantly since 1988, and has now reached levels
(measured by their ozone depleting potential) comparable
to those of 30 years-ago. Because of international
agreements to decrease production and ultimately to phase
out production of CFCs and halons, scientists expect that
total chlorine and bromine concentrations in the
troposphere will peak by 1996 and begin a slow decline
soon thereafter. Concentrations are expected to peak in
the stratosphere 3-5 years later. Increasing ozone losses are
predicted for the remainder of the decade, with gradual
recovery by the mid-21st century.
STATE OF
Worldwide monitoring has shown that stratospheric ozone
has been decreasing for the past two decades or more.
Indicator
Cumulative
U.S. Impact
on the Ozone
Layer
Production (thousand metricians of GFC-11 equivalent}
24000
1960
1965
1970
1975
1980
1985.
;:1990
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1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992'1993 1994
CFC-11
CHgCC'g
CFC-12
CCIk '
Indicator
Atmospheric
Concentration
of Selected
Ozone-
Depleting
Chemicals
Source: Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment (ALE/GAGE)
The average loss across the globe totaled about 5 percent
since the mid-1960s, with cumulative losses of about 10
percent in the winter and spring and a 5 percent loss in the
summer and autumn over North America, Europe, and
Australia. Since the late 1970s, an ozone hole has formed
over Antarctica each austral spring (September/October),
in which up to 60 percent of the total ozone is depleted.
Record low global ozone levels were recorded in 1992 and
1993. These lows were due, in part, to large amounts of
stratospheric sulfate particles from the volcanic eruption of
Mount Pinatubo in the Philippines in 1991; the sulfate
particles temporarily accelerated the ozone depletion
caused by human-made chlorine and bromine compounds.
As expected from the increasing use of CFC substitutes,
observations from several sites have revealed rising
concentrations of these compounds in the atmosphere.
These substitutes have short tropospheric lifetimes, which
tends to reduce their impact on stratospheric ozone as
compared to CFCs and halons. However, some are potent
greenhouse gases.
The link between a decrease in stratospheric ozone and
an increase in surface ultraviolet (UV) radiation at the
Earth's surface has been strengthened during the last
several years by simultaneous measurements of total ozone
and UV radiation in Antarctica and the southern part of
South America during the period of the seasonal ozone
"hole." The measurements show that when total ozone
decreases, UV increases. Furthermore, elevated surface UV
levels in mid-to-high latitudes were observed in the
Northern Hemisphere in 1992 and 1993, corresponding to
Indicator
Ozone
Depletion
Over
Antarctica
Source: National Aeronautics and Space Administration (NASA)
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Indicator
impact of
Montreal
Protocol on
Chlorine
Content of
the
Atmosphere
I fcttxfoe Cbneenteafew (parts per fetoj
12
1985 1990 1995 2000 2005 2010 2015 2020 2025 2030
—— Without Controls -<""—'• 1996 Phaseout
the low ozone levels of those years. However, the lack of
long-term monitoring of surface UV levels and
uncertainties introduced by clouds and ground-level
pollutants have precluded the unequivocal identification
of a long-term trend in surface UV radiation.
RESPONSE
Reacting to the environmental threat of ozone depletion,
the nations of the world came together to create a global
treaty, the Vienna Convention for the Protection of the
Ozone Layer. The agreement entered into force in 1988
and the subsequent Montreal Protocol on Substances that
Deplete the Ozone Layer entered into force in 1989.
Currently HO countries are parties to the Montreal
Protocol. The parties to the Protocol decided on a
timetable for countries to reduce and to end their
production and consumption of eight major halocarbons.
The Protocol also provides a ten-year delay in this
timetable for those developing countries consuming less
than 0.3 kilograms per capita.
The Montreal Protocol timetable was accelerated in
1990 and 1992. Amendments were adopted in response to
scientific evidence that stratospheric ozone is depleting
faster than predicted. As part of an effort to speed the
phase-out of production and consumption of
ozone-depleting chemicals, the parties to the Protocol
decided to provide technology transfer and funds from
industrial to developing countries. Under the accelerated
schedule, the production of most controlled gases is to
cease by January 1, 1996. The developing countries,
however, may receive residual production from
industrialized countries not to exceed 15 percent of 1986
levels. Some individual governments have committed to
even earlier phaseout deadlines.
The U.S. Environmental Protection Agency (EPA),
under authority of the U.S. Clean Air Act Amendments
of 1990, issued regulations for the phaseout of production
and importation of ozone-depleting chemicals controlled
under the Protocol through a marketable permit program.
In addition, EPA established controls on refrigerant
recycling to prevent emissions, a ban on nonessential
products, labeling requirements, a program to review safe
alternative substances, and requirements to revise federal
procurement specifications. Under the regulations, surplus
or recycled substances can in general be stored to service
existing machinery.
Because of the importance of the ozone layer and the
complexity of the chemical reactions affecting it, the
condition of the ozone layer must continue to be
monitored.
" Acknowledgements! This bulletin is first in a series of environment indicator bulletins covering major topics of environmental protection. It is a •
produce of a collaboration between die World Resources Institute and the Environmental Indicators Team of BPA's Office of Policy, Planning, and
^Evaluation, Division of Environmental Statistics and Information. This report was prepared in collaboration with the EPA Office of Air and'
Radiation's Stratospheric Protection Division.
For Further Information: Contact Ms. Bonita Crockett, Office of Strategic Planning and Environmental Data, Mail Code 2161, USEPA, 401 M St., SW,,
Washington, D.C 20460 (phone:202-260-4030)
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