EPA
good up high
bad nearby
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good up high
What is Ozone?
Ozone is a gas that occurs both in the
Earth's upper atmosphere and at ground
level. Ozone can be "good" or "bad" for
your health and the environment,
depending on its location in the
atmosphere.
How Can Ozone Be Both Good
and Bad?
Ozone occurs in two layers of the
atmosphere. The layer closest to the Earths
surface is the troposphere. Here, ground-
level or "bad" ozone is an air pollutant that
is harmful to breathe and it damages
crops, trees and other vegetation. It is a
main ingredient of urban smog. The
troposphere generally extends to a level
about 6 miles up, where it meets the
second layer, the stratosphere. The
stratosphere or "good" ozone layer extends
upward from about 6 to 30 miles and
protects life on Earth from the sun's
harmful ultraviolet (UV) rays.
Too little there... Many popular consumer
products like air conditioners and
refrigerators involve CFCs or halons
during either manufacture or use. Over
time, these chemicals damage the earth's
protective ozone layer.
What is Happening to the
"Good" Ozone Layer?
Ozone is produced naturally in the
stratosphere. But this "good" ozone is
gradually being destroyed by man-made
chemicals referred to as ozone-depleting
substances (ODS), including
chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs),
halons, methyl bromide, carbon
tetrachloride, and methyl chloroform.
These substances were formerly used and
sometimes still are used in coolants,
foaming agents, fire extinguishers,
solvents, pesticides, and aerosol
propellants. Once released into the air
these ozone-depleting substances degrade
very slowly. In fact, they can remain
intact for years as they move through the
troposphere until they reach the
stratosphere. There they are broken
down by the intensity of the sun's UV
rays and release chlorine and bromine
molecules, which destroy the "good"
ozone. Scientists estimate that one
chlorine atom can destroy 100,000
"good" ozone molecules.
Even though we have reduced or
eliminated the use of many ODSs, their
use in the past can still affect the
protective Ozone Layer
Siratosphena
Too much here... Cars, trucks, power plants and
factories all emit air pollution that forms ground-
level ozone, a primary component of smog.
protective ozone layer. Research indicates
that depletion of the "good" ozone layer is
being reduced worldwide. Thinning of the
protective ozone layer can be observed
using satellite measurements, particularly
over the Polar Regions.
How Does the Depletion of
"Good" Ozone Affect Human
Health and the Environment?
Ozone depletion can cause increased
amounts of UV radiation to reach the Earth
which can lead to more cases of skin cancer,
cataracts, and impaired immune systems.
Overexposure to UV is believed to be
contributing to the increase in melanoma,
the most fatal of all skin cancers. Since
1990, the risk of developing melanoma has
more than doubled.
UV can also damage sensitive crops, such
as soybeans, and reduce crop yields. Some
scientists suggest that marine
phytoplankton, which are the base of the
ocean food chain, are already under stress
from UV radiation. This stress could have
adverse consequences for human food
supplies from the oceans.
What is Being Done About the
Depletion of "Good" Ozone?
The United States, along with over 180
other countries, recognized the threats
posed by ozone depletion and in 1987
adopted a treaty called the Montreal
Protocol to phase out the production and
use of ozone-depleting substances.
EPA has established regulations to phase
out ozone-depleting chemicals in the
United States. Warning labels must be
placed on all products containing CFCs or
similar substances and nonessential uses of
ozone-depleting products are prohibited.
Releases into the air of refrigerants used in
car and home air conditioning units and
appliances are also prohibited. Some
substitutes to ozone-depleting products
have been produced and others are being
developed. If the United States and other
countries stop producing ozone-depleting
substances, natural ozone production
should return the ozone layer to normal
levels by about 2050.
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bad nearby
What Causes "Bad" Ozone?
Ground-level or "bad" ozone is not
emitted directly into the air, but is created
by chemical reactions between oxides of
nitrogen (NOx) and volatile organic
compounds (VOC) in the presence of
sunlight. Emissions from industrial
facilities and electric utilities, motor
vehicle exhaust, gasoline vapors, and
chemical solvents are some of the major
sources of NOx and VOC.
At ground level, ozone is a harmful
pollutant. Ozone pollution is a concern
during the summer months because strong
sunlight and hot weather result in harmful
ozone concentrations in the air we
breathe. Many urban and suburban
areas throughout the United States have
high levels of "bad" ozone. But many
rural areas of the country are also subject
to high ozone levels as winds carry
emissions hundreds of miles away from
their original sources.
How Does "Bad" Ozone Affect
Human Health and the
Environment?
Breathing ozone can trigger a variety of
health problems including chest pain,
coughing, throat irritation, and
congestion. It can worsen bronchitis,
All other sources
Industrial/
Commercial/
Residential
Fuel Combustion
Utilities
Motor
Vehicles
Sources of NOx
Motor
Vehicles
Consumer Solvents
Industrial/
Commercial
Processes
emphysema, and asthma. "Bad" ozone also
can reduce lung function and inflame the
linings of the lungs. Repeated exposure
may permanently scar lung tissue.
Healthy people also experience difficulty
breathing when exposed to ozone
pollution. Because ozone forms in hot
weather, anyone who spends time outdoors
in the summer may be affected,
particularly children, outdoor workers and
people exercising. Millions of Americans
live in areas where the national ozone
health standards are exceeded.
Ground-level or "bad" ozone also damages
vegetation and ecosystems. It leads to
reduced agricultural crop and commercial
forest yields, reduced growth and
survivability of tree seedlings, and
increased susceptibility to diseases, pests
and other stresses such as harsh weather.
In the United States alone, ground-level
ozone is responsible for an estimated $500
million in reduced crop production each
year. Ground-level ozone also damages the
foliage of trees and other plants, affecting
the landscape of cities, national parks and
forests, and recreation areas.
What is Being Done About
"Bad" Ozone?
Under the Clean Air Act, EPA has set
protective health-based standards for ozone
in the air we breathe. EPA, states, and cities
have instituted a variety of multi-faceted
programs to meet these health-based
standards. Throughout the country,
additional programs are being put into place
to cut NOx and VOC emissions from
vehicles, industrial facilities, and electric
utilities. Programs are also aimed at reducing
pollution by reformulating fuels and
consumer/commercial products, such as
paints and chemical solvents, that contain
VOC. Voluntary programs also encourage
communities to adopt practices, such as
carpooling, to reduce harmful emissions.
We live with ozone every day. It can
protect life on earth or harm it, but
we have the power to influence
Sources of VOC
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actions you can t a k
High-Altitude "Good" Ozone
• Protect yourself against sunburn. When the UV Index is
"high" or "very high": Limit outdoor activities between 10
am and 4 pm, when the sun is most intense. Twenty minutes
before going outside, liberally apply a broad-spectrum
sunscreen with a Sun Protection Factor (SPF) of at least 15.
Reapply every two hours or after swimming or sweating. For
UV Index forecasts, check local media reports or visit:
www. epa.gov/sunwise/ uvindex.html
• Use approved refrigerants in air conditioning and
refrigeration equipment. Make sure technicians that work on
your car or home air conditioners or refrigerator are certified
to recover the refrigerant. Repair leaky air conditioning units
before refilling them.
Ground-Level "Bad" Ozone
• Check the air quality forecast in your area. At times when the Air
Quality Index (AQI) is forecast to be unhealthy, limit physical exertion
outdoors. In many places, ozone peaks in mid-afternoon to early
evening. Change the time of day of strenuous outdoor activity to avoid
these hours, or reduce the intensity of the activity. For AQI forecasts,
check your local media reports or visit: www.epa.gov/airnow
• Help your local electric utilities reduce ozone air pollution by
conserving energy at home and the office. Consider setting your
thermostat a little higher in the summer. Participate in your local
utilities' load-sharing and energy conservation programs.
• Reduce air pollution from cars, trucks, gas-powered lawn and garden
equipment, boats and other engines by keeping equipment properly
tuned and maintained. During the summer, fill your gas tank during
the cooler evening hours and be careful not to spill gasoline. Reduce
driving, carpool, use public transportation, walk, or bicycle to reduce
ozone pollution, especially on hot summer days.
• Use household and garden chemicals wisely. Use low VOC paints
and solvents. And be sure to read labels for proper use and disposal.
For air program
information,
contact
your Regional
EPA Office:
...or visit EPA's website at
http://www.epa.gov/air
about the cover.
Region 8-(800) 227-8917
www.epa.gov/region8/
Region 2 - (212) 637-4249
www.epa.gov/region2/
Region 5-(312) 353-2211
www.epa.gov/region5/
Region 1C
www.epa.gt
Region 1 -(617)918-1660
www.epa.gov/region1/
EPA Headquarters
(202) 564-7400
http://www.epa.gov/air
Region 3-(215) 814-2100
www.epa.gov/region3/
Region 9 - (415) 947-871
www.epa.gov/region9/
Region 4 - (404) 562-9077
www.epa.gov/region4/
Region 6 - (214) 665-7229
www.epa.gov/region6/
IP: The "good" ozone layer in the stratosphere protects life on Earth from the Sun's
harmful ultraviolet (UV) rays.
OLE: Antarctic Ozone Thinning—shown in blue and purple, extended out over 16
million square miles or about the same size as North America (2001 NASA satellite
image).
OM: "Bad" ozone at ground-level is harmful to breathe and damages crops, trees,
and other vegetation.
United States
Environmental
Protection Agency
Office of Air and Radiation
MCB101A
1200 Pennsylvania Avenue, NW
Washington, DC 20460
EPA-451/K-03-001
June 2003
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