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Brief Questions
and Answers on Ozone Depletion
What is the ozone layer and why
is it important?
The ozone layer is a
concentration of ozone molecules in the stratosphere. About 90% of the planet's
ozone is in the ozone layer. The layer of the Earth's atmosphere that surrounds
us is called the troposphere. The stratosphere, the next higher layer, extends
about 10-50 kilometers above the Earth's surface. Stratospheric ozone is a
naturally-occurring gas that filters the sun's ultraviolet (UV) radiation. A
diminished ozone layer allows more radiation to reach the Earth's surface. For
people, overexposure to UV rays can lead to skin cancer, cataracts, and weakened
immune systems. Increased UV can also lead to reduced crop yield and disruptions
in the marine food chain. UV also has other harmful effects.
How does ozone depletion
occur?
It is caused by the release of
chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODS), which
were used widely as refrigerants, insulating foams, and solvents. The discussion
below focuses on CFCs, but is relevant to all ODS. Although CFCs are heavier
than air, they are eventually carried into the stratosphere in a process that
can take as long as 2 to 5 years. Measurements of CFCs in the stratosphere are
made from balloons, aircraft, and satellites.
When CFCs reach the stratosphere,
the ultraviolet radiation from the sun causes them to break apart and release
chlorine atoms which react with ozone, starting chemical cycles of ozone
destruction that deplete the ozone layer. One chlorine atom can break apart more
than 100,000 ozone molecules.
Other chemicals that damage the
ozone layer include methyl bromide (used as a pesticide), halons (used in fire
extinguishers), and methyl chloroform (used as a solvent in industrial processes
for essential applications). As methyl bromide and halons are broken apart, they
release bromine atoms, which are 40 times more destructive to ozone molecules
than chlorine atoms.
How do we know that natural
sources are not responsible for ozone depletion?
While it is true that
volcanoes and oceans release large amounts of chlorine, the chlorine from these
sources is easily dissolved in water and washes out of the atmosphere in rain.
In contrast, CFCs are not broken down in the lower atmosphere and do not
dissolve in water. The chlorine in these human-made molecules does reach the
stratosphere. Measurements show that the increase in stratospheric chlorine
since 1985 matches the amount released from CFCs and other ozone-depleting
substances produced and released by human activities.
What is being done about ozone
depletion?
In 1978, the use of CFC
propellants in spray cans was banned in the U.S. In the 1980s, the Antarctic
"ozone hole" appeared and an international science assessment more
strongly linked the release of CFCs and ozone depletion. It became evident that
a stronger worldwide response was needed. In 1987, the Montreal Protocol was
signed and the signatory nations committed themselves to a reduction in the use
of CFCs and other ozone-depleting substances.
Since that time, the treaty has
been amended to ban CFC production after 1995 in the developed countries, and
later in developing countries. Today, over 180 countries have ratified the
treaty. Beginning January 1, 1996, only recycled and stockpiled CFCs will be
available for use in developed countries like the US. This production phaseout
is possible because of efforts to ensure that there will be substitute chemicals
and technologies for all CFC uses.
EPA coordinates numerous
regulatory programs designed to help the ozone layer and continues to be active
in developing international ozone protection policies. Individuals can also
help, primarily by ensuring that technicians working on air conditioning and
refrigeration equipment are certified by EPA, that refrigerants are recaptured
and not released, and by educating themselves about the issue of ozone
depletion. A longer article explains EPA's ozone protection efforts in more
detail.
Is there general agreement among
scientists on the science of ozone depletion?
Yes. Under the sponsorship of the
UN Environment Programme (UNEP) and the World Meteorological Organization (WMO),
the scientific community issues periodic reports. Almost 300 scientists
worldwide drafted and reviewed the WMO/UNEP Scientific Assessment of Ozone
Depletion: 2002. An international consensus about the causes and effects of
ozone depletion has emerged.
Will the ozone layer
recover?
Can we make more ozone to fill in
the hole? The answers, in order, are: yes and no. We can't make enough ozone to
replace what's been destroyed, but provided that we stop producing
ozone-depleting substances, natural ozone production reactions should return the
ozone layer to normal levels by about 2050. It is very important that the world
comply with the Montreal Protocol; delays in ending production could result in
additional damage and prolong the ozone layer's recovery.
http://www.epa.gov/docs/ozone/index.html
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