£EPA
UNITED STATES
ENVIRONMENTAL PROTECTION
AGENCY
AIR AND RADIATION
6205J
EPA 430-F-95-001
APRIL 1995
OZONE
DEPLETION
UV INDEX
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The ozone layer forms a thin shield in the stratosphere, protecting life on earth from the sun's
harmful ultraviolet (UV) rays. In the 1980s, scientists began accumulating evidence that the ozone
layer was being depleted. Depletion of the ozone layer can result in increased UV radiation reaching
the earth's surface, which can lead to greater chance of overexposure to UV and the consequent health
effects, including skin cancer, cataracts, and immune suppression.
HOW STRATOSPHERIC OZONE PROTECTS US
Ozone is a naturally occurring gas found in the earth's atmosphere that absorbs certain wavelengths
of the sun's UV radiation. Ozone is concentrated in a part of the atmosphere called the stratosphere.
Stratospheric ozone is most concentrated between 6-30 miles above the earth's surface.
Ozone is formed when oxygen molecules absorb UV radiation and split apart into two oxygen
atoms (0), which combine with other oxygen molecules (O2), to form ozone molecules (0,). Ozone is
also broken apart as it absorbs UV radiation. In this way, UV helps sustain the natural balance of ozone
in the stratosphere, while ozone in turn absorbs UV, protecting life on earth from harmful radiation.
OZONE DEPLETION
Chlorofluorocarbons (CFCs) are used widely in industry and elsewhere as refrigerants, insulating
foams, and solvents. They migrate into the upper atmosphere after use. Because they are heavier than
air, they have to be carried by air currents into the stratosphere, a process that can take as long as 5 to
10 years. These chemicals absorb UV radiation, break apart, and react with ozone, taking one oxygen
atom away and forming highly reactive chlorine monoxide. Chlorine monoxide (CIO) in turn breaks
down 0, again by pulling away a single oxygen atom, creating two O2 molecules, and allowing the Cl
to move freely to another ozone molecule. In this way 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 compounds also damage the ozone layer in much the same way as do CFCs. These 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 ABOUT OZONE DEPLETION
Countries around the world have recognized the threats posed by ozone depletion and have
responded by adopting the Montreal Protocol on Substances That Deplete the Ozone Layer. Parties to
this treaty, including the United States, are phasing out the production of ozone-depleting substances.
EFFECT OF OZONE LAYER DEPLETION ON UV RADIATION LEVELS
Scientists predict that CFC levels should peak by the turn of the century and should fall to 1979
levels between the years 2020 and 2050. As international control measures reduce the release of CFC's
and other ozone depleting substances, the natural atmospheric process will repair the ozone layer. Until
that time, we can expect increased levels of UV at the Earth's surface. These increased UV radiation levels
can lead to a greater chance of overexposure to UV radiation and the consequent health effects.
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ABOUT THE UV INDEX
The UV Index, developed hy the National Weather Service and the Environmental Protection Agency, provides a forecast of the expecte
risk of overexposure to the sun and indicates the degree of caution you should take when working, playing, or exercising outdoors. The
Index predicts exposure levels on a 0 - 10+ scale, where 0 indicates a minimal risk of overexposure, and 10+ means a very high risk of overex
posure. Calculated on a next-day basis tor dozens of cities across the U.S. hy the National Weather Service, the UV Index takes into account
clouds and other local conditions that affect the amount of UV radiation reaching the ground in different pans of the country.
BE SUN WISE
The goals of the UV Index Program are to:
1. Raise awareness of the risks from overexposure to the sun's UV radiation;
2. Provide people in all parts of the U.S. with the information they need to protect themselves from overexposure; and
3. Ultimately reduce the incidence of skin cancer, cataracts, and other lA'-related health problems.
FOR MORE INFORMATION
To learn more about the UV Index, the ozone layer, and actions being taken to prevent ozone depletion, call EPA's Stratospheric
Ozone Hotline at (800) 296-1996.
The use and emission of ozone-depleting substances damages the stratospheric ozone layer,
allowing more ultraviolet rays to reach the earth's surface and cause adverse human health effects.
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