- What is the ozone layer and why is it important?
- The ozone layer is a
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 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
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.
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
(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
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
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
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
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. To
obtain a copy of the executive summary of the assessment, please visit
NOAA's web site
- 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
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. More detail on these
questions is provided
elsewhere on this web site