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)
hydrofluorocarbons (HCFCs, 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 and HCFCs 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 60 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 multiple times to
accelerate the phaseout
of CFCs, HCFCs, and other ozone depleting substances. Today, over 190
countries have ratified the treaty. For over a decade the production of
CFCs has been banned, with limited exceptions for essential uses.
The next step in the elimination of ozone depleting substances occurs
in 2010 when EPA will ban the production of the most harmful HCFCs.
This production phaseout is possible because of efforts to ensure
that there are substitute chemicals and technologies for the compounds
being phased out.
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, an international consensus about the causes and effects of ozone
depletion has emerged.
Under the sponsorship of the UN Environment Programme (UNEP) and the
World Meteorological Organization (WMO), the scientific community issues
periodic reports on the science of ozone depletion.
Over 300 scientists worldwide drafted and reviewed the most recent
analysis, WMO/UNEP Scientific Assessment of Ozone Depletion: 2006.
Will the ozone layer recover? Can we
make more ozone to fill in the hole?
Provided that we stop producing ozone-depleting substances, ozone
will be created through natural processes that 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.
Courtesy: United
States Environmental Protection Agency |