v>EPA
United States
Environmental Protection
Agency
Air and Radiation
6205J
Ozone Depletion
EPA430-F-99-023
September 1999
www.epa.gov/sunwise
The ozone layer forms a thin shield in the upper atmosphere, protecting life on
Earth from the sun's ultraviolet (UV) rays. In the 1980s, scientists began accu-
mulating evidence that the ozone layer was being depleted. Depletion of the
ozone layer results in increased UV radiation reaching die Earth's surface, which
in turn can lead to a greater chance of overexposure to UV radiation and the
related health effects of skin cancer, cataracts, and immune suppression.
What Is Stratospheric Ozone?
Ozone is a naturally occurring gas that is found in two layers of the atmosphere.
In the layer surrounding the Earth's surface—the troposphere—ground-level or
"bad" ozone is an air pollutant that is a key ingredient of urban smog. The tro-
posphere extends up to the stratosphere, which is where "good" ozone protects
life on Earth by absorbing some of the sun's UV rays. Stratospheric ozone is
most concentrated between 6 to 30 miles above the Earth's surface.
Ozone Depletion
Until recently, chlorofluorocarbons (CFCs) were used widely in industry and
elsewhere as refrigerants, insulating foams, and solvents. Strong winds carry
CFCs into the stratosphere in a process that can take as long as 2 to 5 years.
When CFCs break down in the stratosphere, they release chlorine, which
attacks ozone. Each chlorine atom acts as a catalyst, repeatedly combining with
and breaking apart as many as 100,000 ozone molecules during its stratospheric
life.
Other ozone-depleting substances include pesticides such as methyl bromide,
halons used in fire extinguishers, and methyl chloroform used in industrial
processes.
What Is Being Done?
Countries around the world, including the United States, have recognized the
threats posed by ozone depletion and adopted a treaty called the Montreal
Protocol to phase out the production and use of ozone-depleting substances.
How Ozone Depletion Affects UV Levels
Scientists predict that ozone depletion should peak between 2000 and 2010. As
international control measures reduce the release of CFCs and other ozone-
depleting substances, natural atmospheric processes will repair the ozone layer
around the middle of the 21st century. Until that time, we can expect increased
levels of UV radiation at the Earth's surface. These increased UV levels can lead
to a greater risk of overexposure to UV radiation and related health effects.
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EPA's SunWise School
Program ^
In response to the serious public
health threat posed by exposure to °1' PV° '
increased UV levels, the U.S. Environmental
Protection Agency (EPA) is working with schools
and communities across the nation through the
SunWise School Program. SunWise aims to teach
children in elementary school and their caregivers
about ozone depletion, UV radiation, and how to
protect themselves from overexposure to the sun.
For More Information
To learn more about the ozone layer, the SunWise
School Program, and actions being taken to prevent
ozone depletion, call EPA's Stratospheric Ozone
Information Hotline at 800 296-1996 or visit our
Web site at .
The use and emission of ozone-depleting substances
damages the stratospheric ozone layer, which allows
more UV rays to reach the Earth's surface and cause
adverse human health effects.
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