TOP: The “good” ozone layer in the stratosphere protects life on Earth from the Sun’s

harmful ultraviolet (UV) rays.

MIDDLE: 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).

BOTTOM: “Bad” ozone at ground-level is harmful to breathe and damages crops, trees,

and other vegetation.

For air program

information,

contact

your Regional

EPA Office:

...or visit EPA’s website at

http://www.epa.gov/air

PRINTED ON RECYCLED PAPER

United States

Environmental

Protection Agency

EPA-451/K-03-001

June 2003

Office of Air and Radiation

MC6101A

1200 Pennsylvania Avenue, NW

Washington, DC 20460

about the cover...

actions you can take

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.

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EPA Headquarters

(202) 564-7400

http://www.epa.gov/air

Region 1 - (617) 918-1660

www.epa.gov/region1/

Region 2 - (212) 637-4249

www.epa.gov/region2/

Region 4 - (404) 562-9077

www.epa.gov/region4/ Region 6 - (214) 665-7229

www.epa.gov/region6/

Region 7 - (913) 551-7020

www.epa.gov/region7/

Region 5 - (312) 353-2211

www.epa.gov/region5/

Region 8 - (800) 227-8917

www.epa.gov/region8/

Region 10 - (206) 553-1505

www.epa.gov/region10/

Region 9 - (415) 947-8715

www.epa.gov/region9/

http://www.ep

Region 3 - (215) 814-2100

www.epa.gov/region3/
Motor

Vehicles

Utilities

All other sources

Industrial/

Commercial/

Residential

Fuel Combustion

Sources of NOx

bad nearby

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.

good up high

Too much here... Cars, trucks, power plants and

factories all emit air pollution that forms groundlevel ozone, a primary component of smog.

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.

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 Earth’s

surface is the troposphere. Here, groundlevel 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.

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. 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.

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,

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.

Motor

Vehicles

Industrial/

Commercial

Processes

Consumer Solvents

Sources of VOC