Air Quality
Index
Good
(0-50)
Moderate
(51-100)
Unhealthy for
Sensitive Groups
(101-150)
Unhealthy
(151-200)
Very Unhealthy
(201-300)
Protect Your Health
No health impacts are expected when air quality is in this range.
Unusually sensitive people should consider limiting prolonged outdoor exertion.
The following groups should limit prolonged outdoor exertion:
• People with lung disease, such as asthma
• Children and older adults
• People who are active outdoors
The following groups should avoid prolonged outdoor exertion:
• People with lung disease, such as asthma
• Children and older adults
• People who are active outdoors
Everyone else should limit prolonged outdoor exertion.
The following groups should avoid all outdoor exertion:
• People with lung disease, such as asthma
• Children and older adults
• People who are active outdoors
Everyone else should limit outdoor exertion.
How can you know when ozone levels are
unhealthy?
Checking local air quality is as easy as checking the
weather forecast. You can find daily ozone forecasts and
real-time ozone conditions for over 300 cities across
the country at the AIRNow Web site: airnow.gov. You
may also find air quality reported in your newspapers
weather section or on radio or television, particularly
when conditions are unhealthy. All of these sources use
the Air Quality Index (or AQI) to report levels of ozone
and other common pollutants in the air. The AQI, shown
above, is a simple color-coded scale. For example, yellow
means "moderate" conditions and red means "unhealthy"
conditions. This color scheme can help you know, at a
glance, if air pollutants are reaching unhealthy levels in
your area. The illustration to the right shows how you
might see the AQI used in a newspaper.
AQI in a Newspaper—Example
AIR QUALITY INDEX
^H Pollutant: Ozone
U Today's Forecast: 180
Sffla Quality: Unhealthy
When air quality is unhealthy,
everyone is at risk—especially
sensitive groups.
Today's air quality is forecast as unhealthy
due to ozone. Hot, sunny weather and
stagnant air are expected to cause ozone in
Center City to rise to unhealthy levels.
Visitairnow.gov
D Check daily ozone levels
Access air quality resources
Ozone and
Your Health
EnviroFlash
Your Environmental News Flash
Sign up for EnviroFlash, a free service that
will alert you via email when air quality
is forecast to be a concern.
Learn about air quality
in your area: How does it
compare with other areas? Has
it improved? What time of year
has the best air quality?
Compare Air Quality of "-U.S. Cities
Adults, students, and kids:
Access brochures, movies, games,
and other resources. Learn about
air quality, protecting your health,
and how to reduce air pollution.
Health care providers, teachers, and
weathercasters: Access training and
tools to help adults and children
understand how air pollution affects
their health and how they can protect
themselves.
Link to Web cameras
that provide real-time
pictures of visibility at
many locations across the
United States.
United States Environmental Protection Agency
Air and Radiation
Washington, DC 20460
February 2009
EPA-456/F-09-001
What Is Ozone?
Are You at Risk?
How Can You Protect Yourself?
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Ozone, the main ingredient of smog,
presents a serious air quality
problem in many parts of the United
States. Even at low levels, ozone can cause
health effects. You can take simple steps,
described in this pamphlet, to protect your
health from ozone.
What is ozone?
Ozone is a colorless gas found in the air we breathe. Ozone is
good or bad, depending where it occurs.
Good ozone is present naturally in the Earth's upper
atmosphere—10 to 30 miles above the Earth's surface. This
natural ozone shields us from the sun's harmful ultraviolet rays.
Bad ozone forms near ground level when air pollutants
(emitted by sources such as cars, power plants, and chemical
plants) react chemically in the presence of sunlight. Ozone
pollution is more likely to form during warmer months. This
is when the weather conditions normally needed to form
ground-level ozone—lots of sun—occur.
Are you at risk from ground-level ozone?
Several groups of people are particularly sensitive to ozone,
especially when they are active outdoors. This is because ozone
levels are higher outdoors, and physical activity causes faster and
deeper breathing, drawing more ozone into the body.
In general, as concentrations of ground-level ozone increase,
both the number of people affected and the seriousness of the
health effects increase. Also, more people with lung disease
visit doctors or emergency rooms and are admitted to the
hospital. When ozone levels are very high, everyone should be
concerned about ozone exposure.
People who may be particularly sensitive to ozone include:
People with lung diseases, such as asthma, chronic bronchitis,
and emphysema will generally experience more serious health
effects at lower ozone levels.
Children are at higher risk from ozone exposure because:
• They often play outdoors in summer when ozone levels are
higher.
• They are more likely to have asthma, which may be
aggravated by ozone exposure.
• Their lungs are still developing.
Older adults may be more affected by ozone exposure,
possibly because they are more likely to have pre-existing
lung disease.
Active people of all ages who exercise or work vigorously
outdoors have higher exposure to ozone than people who are
less active.
Some healthy people are more sensitive to ozone. They
may experience health effects at lower ozone levels than the
average person even though they have none of the risk factors
listed above. There may be a genetic basis for this increased
sensitivity.
People of all ages who are active outdoors are at risk from
ozone exposure.
How can ground-level ozone affect your health?
Ozone can:
• Irritate your respiratory system. When this happens,
you may cough, feel irritation or soreness in your throat, or
experience chest tightness or pain when taking a deep breath.
• Reduce lung function. This can make it more difficult for
you to breathe as deeply and vigorously as you normally
would, especially when exercising. You may notice that
breathing starts to feel uncomfortable and that you are
taking more rapid and shallow breaths than normal.
• Inflame and damage cells that line your lungs. Within
a few days, the damaged cells are replaced and the old
cells are shed—much like the way your skin peels after a
sunburn.
• Make your lungs more susceptible to infection.
• Aggravate asthma. When ozone levels are unhealthy,
more people with asthma have symptoms that require
a doctor's attention or the use of medication. Ozone
makes people more sensitive to allergens—the most
common triggers for asthma attacks. Also, asthmatics
may be more severely affected by reduced lung function
and airway inflammation. People with asthma should
have an asthma action plan and follow it carefully when
ozone levels are unhealthy.
• Aggravate other chronic lung diseases such as
emphysema and chronic bronchitis.
• Cause permanent lung damage. Repeated short-term
ozone damage to children's developing lungs may lead
to reduced lung function in adulthood. In adults, ozone
exposure may accelerate the natural decline in lung
function that occurs with age.
Many of these effects can lead to increased school or work
absences, visits to doctors and emergency rooms, and hospital
admissions. Research also indicates that ozone exposure
can increase the risk of premature death from heart or lung
disease, although more research is needed to understand how
ozone may affect the heart and cardiovascular system.
When ozone levels may be unhealthy—for example on
hot sunny days—notice whether you have any respiratory
symptoms. If you do, take steps to protect your health, as
described below.
Are there always symptoms?
People living in areas where ozone levels are frequently
unhealthy may find that their initial symptoms go away over
time—particularly when exposure to unhealthy ozone levels
continues for several days. However, ozone can continue to
Ozone can inflame the lung's lining. These photos show a
healthy lung airway (left) and an inflamed lung airway (right).
Photos courtesy of PENTAX Medical Company.
damage the lungs even when the symptoms are no longer
noticeable. The best way to protect your health is to find out
when ozone levels are elevated in your area and take simple
steps to minimize your exposure—even when you don't feel
obvious symptoms.
How can you avoid unhealthy exposure to ozone?
When ground-level ozone is at unhealthy levels, your chances of
being affected increase the longer you are active outdoors and the
more strenuous your activity. Since exercise is good for health, it's
important to stay active and know when to make changes. When
ozone levels are unhealthy, protect your health by:
• Reducing the time you are active outdoors.
• Scheduling the activity for the morning or evening when
ozone levels are usually lower.
• Substituting a less intense activity. For example, go for a
walk instead of a jog. For each person, intensity depends
on physical fitness, but typically:
» Less intense activities include things like climbing stairs,
playing tennis or baseball, simple garden or construction
work, and light jogging, cycling, or hiking.
» More intense activities include playing basketball
or soccer, chopping wood, heavy manual labor, and
vigorous running, cycling, or hiking.
No matter how fit you are, cutting back on the level or
duration of outdoor activity when ozone levels are unhealthy
will help protect you from ozone's harmful effects.
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