United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA/451-K-97-002
October .1997
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What is Ozone?
Ozone is a gas that forms in the
atmosphere when 3 atoms of oxygen
are combined (03). It is not emitted
directly into the air, but at ground level
is created by a chemical reaction
between oxides of nitrogen (NO^), and
volatile organic compounds (VOC) in
the presence of sunlight. Ozone has die
same chemical structure whether it
occurs high above the earth or at
ground level and can be "good" or
'"bad," depending on its location in
the atmosphere.
How Can Ozone Be Both
Good and Bad?
Ozone occurs in two layers of die
atmosphere. The layer surrounding the
earth's surface is die troposphere. Here,
ground-level or "bad" ozone is an air
pollutant that damages human health,
vegetation, and many common
materials. It is a key ingredient of urban
smog. The troposphere extends to a
level about 10 miles up, where it meets
the second layer, the stratosphere. The
stratospheric or "good" ozone layer extends
upward from about 10 to 30 miles and
protects life on eartli from the sun's
harmful ultraviolet rays (UV-b).
What is Happening to the
"Good" Ozone Layer?
Ozone occurs naturally in the stratosphere
and is produced and destroyed at a
constant rate. But this "good" ozone is
gradually being destroyed by manmade
chemicals called chlorofluorocarbons
(CFCs), halons, and other ozone depleting
substances (used in coolants, foaming
agents, fire extinguishers, solvents, and
aerosol propellants). These ozone depleting
substances degrade slowly and can remain
intact for many years as they move
through the troposphere until they reach
die stratosphere. There they are broken
down by die intensity of the sun's ultravio-
let rays and release chlorine and bromine
molecules, which destroy "good" ozone.
One chlorine or bromine molecule can
destroy 100,000 ozone molecules, causing
ozone to disappear much faster than
nature can replace it.
Too much here... Cars, trucks, power plants and
factories all emit air pollution that forms ground-
ievel ozone or smog,
Too little there... Many popular consumer products
like air conditioners and refrigerators involve CFCs or
halons during either manufacture or use. These
chemicals damage the earth's protective ozone layer.
It can take years for ozone depleting
chemicals to reach die stratosphere, and
even though we have reduced or elimi-
nated the use of many CFCs, their
impact from years past is just starting to
affect the ozone layer. Substances released
into the air today will contribute to
ozone destruction well into the future.
Satellite observations indicate a world-
wide diinning of die protective ozone
layer. The most noticeable losses occur
over die North and South Poles because
ozone depletion accelerates in extremely
cold weather conditions.
How Does the Depletion
of "Good" Ozone Affect
Human Health and the
Environment?
As the stratospheric ozone layer is
depleted, higher UV-b levels reach the
earth's surface. Increased UV-b can lead
to more cases of skin cancer, cataracts,
and impaired immune systems. Damage
to UV-b sensitive crops, such as soybeans,
reduces yield. High altitude ozone
depletion is suspected to cause decreases
in phytoplankton, a plant that grows in
the ocean. Phytoplankton is an impor-
tant link in the marine food chain and,
therefore, food populations could
decline. Because plants "breathe in"
carbon dioxide and "breathe out" oxygen,
carbon dioxide levels in the air could also
increase. Increased UV-b radiation can be
instrumental in forming more ground-
level or "bad" ozone.
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What is Being Done
About the Depletion of
Good Ozone?
The Montreal Protocol, a series of
international agreements on the
reduction and eventual elimination of
production and use of ozone depleting
substances, became effective in 1989.
Currently, 160 countries participate in
the Protocol. Efforts will result in
recovery of the ozone layer in
about 50 years.
In the United States, the U.S. Environ-
mental Protection Agency (EPA)
continues to establish regulations to
phase out these chemicals. The Clean
Air Act requires warning labels on all
products containing CFCs or similar
substances, prohibits nonessential
ozone depleting products, and
prohibits the release of refrigerants
used in car and home air conditioning
units and appliances into the air.
What Causes "Bad" Ozone?
Motor vehicle exhaust and industrial
emissions, gasoline vapors, and
chemical solvents are some of the
major sources of NOx and VOC, also
known as ozone precursors. Strong
Sources of VOC
sunlight and hot weather cause ground-
level ozone to form in harmful concen-
trations in the air. Many urban areas
tend to have high levels of "bad" ozone,
but other areas are also subject to
high ozone levels as winds carry NOx
emissions hundreds of miles away from
their original sources.
Ozone concentrations can vary from year
to year. Changing weather patterns
(especially the number of hot, sunny
days), periods of air stagnation, and
other factors that contribute to
ozone formation make long-term
predictions difficult.
How Does "Bad" Ozone
Affect Human Health and the
Environment?
Repeated exposure to ozone pollution
may cause permanent damage to the
lungs. Even when ozone is present in low
levels, inhaling it triggers a variety of
health problems including chest pains,
coughing, nausea, throat irritation, and
congestion. It also can worsen bronchitis,
heart disease, emphysema, and asthma,
and reduce lung capacity.
Healthy people also experience difficulty
in breathing when exposed to ozone
pollution. Because ozone pollution
usually forms in hot weather, anyone
who spends time outdoors in the
summer may be affected, particularly
children, the elderly, outdoor workers
and people exercising. Millions of
Americans live in areas where the
national ozone health standards
are exceeded.
Ground-level ozone damages plant life
and is responsible for 500 million dollars
in reduced crop production in the United
States each year. It interferes with the
ability of plants to produce and store
food, making them more susceptible to
disease, insects, other pollutants, and
Sources of NOx
harsh weather. "Bad" ozone damages the
foliage of trees and other plants, ruining the
landscape of cities, national parks and
forests, and recreation areas.
What is Being Done About
Bad Ozone?
The Clean Air Act Amendments of
1990 require EPA, states, and cities to
implement programs to further reduce
emissions of ozone precursors from
sources such as cars, fuels, industrial
facilities, power plants, and consumer/
commercial products. Power plants will be
reducing emissions, cleaner cars and fuels
are being developed, many gas stations are
using special nozzles at the pumps to
recapture gasoline vapors, and vehicle
inspection programs are being improved
to reduce emissions.
The ultimate responsibility for our
environment is our own. Minor lifestyle
changes can result in major air quality
improvements.
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High-Altitude "Good" Ozone
* Make sure that technicians working on your car air
conditioner, home air conditioner, or refrigerator are
certified by an EPA approved program to recover the
refrigerant (this is required by law).
* Have your car and home air conditioner units and
refrigerator checked for leaks. When possible, repair
leaky air conditioning units before refilling them.
• Contact local authorities to properly dispose
of refrigeration or air conditioning equipment.
* Protect yourself against sunburn. Minimize sun
exposure during midday hours (10 am to 4 pm).
Wear sunglasses, a hat with a wide brim, and protec-
tive clothing with a tight weave. Use a broad spec-
trum sunscreen with a sun protection factor (SPF) of
at lease 15 and 30 is better.
Ground-Level "Bad" Ozone
• Keep your automobile well tuned and maintained.
• Carpool, use mass transit, walk, bicycle, and/or reduce
driving, especially on hot summer days.
• Be careful not to spill gasoline when filling up your car or
gasoline-powered lawn and garden equipment. During the
summer, fill your gas tank during the cooler evening hours.
• Make sure your car's tires are properly inflated and your
wheels are aligned.
• Participate in your local utility's energy conservation
programs.
• Seal containers of household cleaners, workshop chemicals
and solvents, and garden chemicals to prevent VOC from
evaporating into the air. Dispose of them properly.
We live with ozone every day. it can protect life on earth or harm it, but
we have the power to influence ozone's impact by the way we live.
For more information, contact the following EPA Offices:
EPA Headquarters
L;:S, EPA
.;ni M, Street, SW
':;jshington, DC 20460
' ,102 > 260-7400
t ,b, EPA Region 1
'Connecticut, Massachusetts,
.Ntiilnc, New Hampshire,
Kh-nJc island, Vermont)
John It Kennedy Federal Building
Room 2203
ji'jiion, MA 02203
I .".S. EPA Region 2
Nv\v Jersey, New York,
t'tsono Rko, Virgin Islands)
I'-'"'.; Rro.i-Jwjy
:,,v, York, NY i 000% 1866
U.S. EPA Region 3
(Delaware, Maryland,
Pennsylvania, Virginia,
West Virginia, District
of Columbia)
841 Chestnut Building
Philadelphia, PA 19107
(215) 566-2100
U.S. EPA Region 4
(Alabama, Florida, Georgia,
Kentucky, Mississippi, _
North Carolina, South
Carolina, Tennessee)
Atlanta Federal Center
61 Forsyth Street
Adanta, GA 30303
(404) 562-9077
U.S. EPA Region 5
(Illinois, Indiana, Michigan,
Minnesota, Ohio, Wisconsin)
77 West Jackson Boulevard
Chicago, IL 60604
(312) 353-2212
U.S. EPA Region 6
(Arkansas, Louisiana,
New Mexico, Oklahoma, Texas)
1445 Ross Avenue, 12th Floor
Suite 1200
Dallas, TX 75202-2733
(214)665-7220
U.S. EPA Region 7
(Iowa, Kansas, Missouri,
Nebraska)
726 Minnesota Avenue
Kansas City, KS 66101
(913) 551-7020
U.S. EPA Region 8
(Colorado, Montana,
North Dakota, South Dakota,
Utah, Wyoming)
999 18da Street, Suite 500
Denver, CO 80202-2405
(303) 312-6312
U.S. EPA Region 9
(Arizona, California, Hawaii,
Nevada, Guam, American Samoa)
75 Hawthorne Street
San Francisco, CA 94105
(415) 744-1219
U.S. EPA Region 10
(Idaho, Washington, Oregon,
Alaska)
1200 Sixth Avenue
Seattle, WA 98101
(206) 553-1200
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