Index Values
0 to 50
51 to 100
101 to 150
151 to 200
201 to 300
Descriptors
Good
Moderate
Unhealthy
for Sensitive
Groups
Unhealthy
Very Unhealthy
Cautionary Statements for Ozone
None.
Unusually sensitive people should consider limiting prolonged outdoor exertion.
Active children and adults, and people with respiratory disease, such as asthma,
should limit prolonged outdoor exertion.
Active children and adults, and people with respiratory disease, such as asthma,
should avoid prolonged outdoor exertion; everyone else, especially children,
should limit prolonged outdoor exertion.
Active children and adults, and people with respiratory disease, such as asthma,
should avoid all outdoor exertion; everyone else, especially children, should
limit outdoor exertion.
Air Quality Index
The Air Quality Index, or AQI, is a scale used to report
actual levels of ozone and other common pollutants in the
air. The higher the AQI value, the greater the health con-
cern. As shown in the table above, the AQI scale has been
divided into categories that correspond to different levels
of health concern.
A specific color has been assigned to each AQI category.
For example, red means "unhealthy" conditions and
purple means "very unhealthy" conditions. This color
scheme can help you quickly determine if air pollutants
are reaching unhealthy levels in your area.
You may see the AQI for ozone reported in your news-
paper or on your local television or radio station. Here's
the type of report you might hear:
The Air Quality Index today was 160. Air quality
was unhealthy due to ozone. Hot, sunny weather
and stagnant air caused ozone in Center City to rise
to unhealthy kvels.
The illustration below shows how you might see the AQI
used in a newspaper. In this example, an AQI value of 130
is reported, which means that ozone levels are unhealthy
for sensitive groups.
Pollutant: Ozone
Today's Forecast: 130
Quality: Unhealthy for
Sensitive Groups
Children and people with
asthma are the groups
most at risk.
AIRNOW (www.epa.gov/airnow) is an Internet
site that gives daily information about ozone and
how it may affect you. AIRNOW contains:
• Ozone maps that use color contours based on
the AQI to show ozone levels in local areas. You
can use the maps to quickly determine if ozone
concentrations are reaching unhealthy levels.
• Summertime ozone forecasts.
• Ideas about what you can do to reduce ozone
levels, such as driving less, making sure your car
is well-tuned, and participating in local energy
conservation programs.
• Links to state and local air quality programs.
• SMOG—Who Does It Hun?, a booklet that
provides more information about ozone health
effects and how you can protect yourself.
AIR QUALITY INDEX
Maps that provide daily information about ozone levels
are available on the AIRNOW web site.
&EPA Ozone and
Your Health
What Is Ozone, or Smog?
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 a number of respiratory effects.
You can take simple steps, described in this pam-
phlet, to protect your health from ozone.
Ozone is the main ingredient of smog.
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, depending on where it is found.
Good Ozone. Ozone occurs naturally in the Earth's upper
atmosphere—10 to 30 miles above the Earth's surface—
where it shields us from the sun's harmful ultraviolet rays.
Bad Ozone. In the Earth's lower atmosphere, near ground
level, ozone is formed when pollutants emitted by cars,
power plants, chemical plants, and other sources react
chemically in the presence of sunlight. Ozone pollution
is a concern during the summer months when the weather
conditions needed to form ground-level ozone—lots of
sun, hot temperatures—normally occur.
Are you at risk from ground-level ozone?
Several groups of people are particularly sensitive to ozone—
especially when they are active outdoors—because physical
activity causes people to breathe faster and more deeply.
Active children are the group at highest risk from ozone
exposure because they often spend a large part of the sum-
mer playing outdoors. Children are also more likely to
have asthma, which may be aggravated by ozone exposure.
Active adults of all ages who exercise or work vigor-
ously outdoors have a higher level of exposure to ozone
than people who are less active.
People with asthma or other respiratory diseases
that make the lungs more vulnerable to the effects of
ozone will generally experience health effects earlier and
at lower ozone levels than less sensitive individuals.
People with unusual susceptibility to ozone.
Scientists don't yet know why, but some healthy people may
experience health effects at more moderate levels of outdoor
exertion or at lower ozone levels than the average person.
In general, as concentrations of ground-level ozone
increase, more and more people experience health effects,
the effects become more serious, and more people are
admitted to the hospital for respiratory problems. When
ozone levels are very high, everyone should be concerned
about ozone exposure.
Children and adults of all ages who are active outdoors are
at risk from ozone exposure.
Ozone can inflame the lung's lining. These photos show a
healthy lung airway (left) and an inflamed lung airway (right).
How can ground-level ozone
affect your health?
Ozone can irritate your respiratory system, causing
you to start coughing, feel an irritation in your throat and/
or experience an uncomfortable sensation in your chest.
Ozone can reduce lung function and make it more
difficult for you to breathe as deeply and vigorously as you
normally would. When this happens, you may notice that
breathing starts to feel uncomfortable. If you are exercising
or working outdoors, you may notice that you are taking
more rapid and shallow breaths than normal.
Ozone can aggravate asthma. When ozone levels are
high, more people with asthma have attacks that require
a doctor's attention or the use of additional medication.
One reason this happens is that ozone makes people more
sensitive to allergens, which are the most common triggers
for asthma attacks. Also, asthmatics are more severely
affected by the reduced lung function and irritation that
ozone causes in the respiratory system.
Ozone can inflame and damage cells that line your
lungs. Within a few days, the damaged cells are replaced
and the old cells are shed—much in the way your skin
peels after a sunburn.
Ozone may aggravate chronic lung diseases such
as emphysema and bronchitis and reduce the immune
system's ability to fight off bacterial infections in the respi-
ratory system.
Ozone may cause permanent lung damage.
Repeated short-term ozone damage to children's develop-
ing lungs may lead to reduced lung function in adulthood.
In adults, ozone exposure may accelerate the natural
decline in lung function that occurs as part of the normal
aging process.
Are there always symptoms?
Ozone damage also can occur without any noticeable
signs. People who live in areas where ozone levels are
frequently high may find that their initial symptoms go
away over time—particularly when exposure to high ozone
levels continues for several days. Ozone continues to cause
lung damage even when the symptoms have disappeared.
The best way to protect your health is to find out when
ozone levels are elevated in your area and take simple pre-
cautions to minimize exposure even when you don't feel
obvious symptoms.
How can you avoid unhealthy
exposure to ozone?
Your chances of being affected by ozone increase the longer
you are active outdoors and the more strenuous the activity
you engage in. If you're involved in an activity that requires
heavy exertion, you can reduce the time you spend on this
activity or substitute another activity that requires more
moderate exertion (e.g., go for a walk rather than a jog).
In addition, you can plan outdoor activities when ozone
levels are lower, usually in the morning or evening.
Examples of activities that involve moderate exertion
include climbing stairs, playing tennis or baseball, simple
garden or construction work, and light jogging, cycling,
or hiking. Activities that involve heavy exertion include
playing basketball or soccer, chopping wood, heavy manual
labor, and vigorous running, cycling, or hiking. Because
fitness levels vary widely among individuals, what is mod-
erate exertion for one person may be heavy exertion for
another. No matter how fit you are, cutting back on the
level or duration of exertion when ozone levels are high
will help protect you from ozone's harmful effects.
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