United States
Environmental Protection
Agency
EPA-454/R-00-005
June 2000
http://www.epa.gov
Air and Radiation
Washington, DC 20460
Air Quality index
A Guide to
Air Quality and
Your Health
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Increasingly, radio, TV, and newspapers are
providing information like/this to local
"cotrimuhities.,But what does it mean to you
...It you plan to be outdoors that day?
,..!f you have children who play outdoors?
...if you are retired? ...if you have asthma?
This booklet will help you understand what
this information means to you and your family
and what you can do to protect your health.
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A Guide to Air Quality
and Your Health
Local air quality affects how we live and breathe. Like
the weather, it can change from day to day or even hour
to hour. The U.S. Environmental Protection Agency
(EPA) and others are working to make information
about outdoor air quality as available to the public as
information about the weather. A key tool in this effort
is the Air Quality Index, or AQI. EPA and local officials
use the AQI to provide die public with timely and easy-
to-understand information on local air quality and
whedier air pollution levels pose a health concern.,
This booklet tells you about
the AQI and how it is used to
provide air quality information.
It also tells you about die possi-
ble health effects of major air
pollutants at various levels and
suggests actions you can take
to protect your healdi when
pollutants in your area reach
unhealthy concentrations.
WfiaUstSieAQI?
The AQI is an index for
reporting daily air quality. It
tells you how clean or polluted
your air is, and what associated
healdi concerns you should be aware of. The AQI focus-
es on healdi effects diat can happen widiin a few hours
or days after breadiing polluted air. EPA uses the AQI
for five major air pollutants regulated by die Clean Air
Act: ground-level ozone, particulate matter, carbon
monoxide, sulfur dioxide, and nitrogen dioxide. For each
of diese pollutants, EPA has established national air qual-
ity standards to protect against harmful health effects.
Air quality directly affects
our quality of life.
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AIR QUALITY INDEX
How does the AQI work?
You can think of the AQI as a yardstick that runs from
0 to 500. The higher the AQI value, the greater the level
of air pollution and the greater the health danger. For
example, an AQI value of 50 represents good air quality
and litde potential to affect public health, while an AQI
value over 300 represents hazardous air quality.
An AQI value of 100 generally corresponds to the
national air "quality standard for the pollutant, which is
the level EPA has set to protect public health. So, AQI
values below 100 are generally thought of as satisfactory.
When AQI values are above 100, air quality is considered
to be unhealthy—at first for certain sensitive groups of
people, dien for everyone as AQI values get higher.
Understanding tfie AQi
The purpose of the AQI is to help you understand what
local air quality means to your health. To make the AQI
as easy to understand as possible, EPA has divided the
AQI scale into six categories, shown below:
:^ir;OBMaiit£li$^
8&sMK«#»8»lt«fe
51 to 100
Moderate
Yellow,,
Each category corresponds to a different level of health con-
cern. For example, when the AQI for a pollutant is between
51 and 100, the heakh concern is "Moderate." Here are the
six levels of health concern and what they mean:
m "Good" The AQI value for your community is between
0 and 50. Air quality is considered satisfactory and air
pollution poses little or no risk.
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AIR QUALITY INDEX
• "Moderate" The AQI for your community is between
51 and 100. Air quality is acceptable; however, for some
pollutants there may be a moderate health concern for a
very small number of individuals. For example, people
who are unusually sensitive to ozone may experience res-
piratory symptoms.
• "Unhealthy for Sensitive Groups" Certain groups
of people are particularly sensitive to the harmful effects
of certain air pollutants. This means they are likely to be
affected at lower levels than the general public. For exam-
ple, children and adults who are active outdoors and.'
people with respiratory disease are at greater risk from
exposure to ozone, while people with heart disease are
at greater risk from carbon monoxide. Some people may
be sensitive to more than one pollutant. When AQI
values are between 101 and 150, members of sensitive
groups may experience health effects. The general public
is not likely to be affected when the AQI is in this range.
• "Unhealthy" AQI values are between 151 and 200.
Everyone may begin to experience health effects.
Members of sensitive groups may experience more seri-
ous health effects.
• «very Unhealthy" AQI values between 201 and 300
trigger a health alert, meaning everyone may experience
more serious health effects.
" "Hazardous" AQI values over 300 trigger health warn-
ings of emergency conditions. The entire population is
more likely to be affected.
AQIcoSors
EPA has assigned a specific color to each AQI category
to make it easier for people to understand quickly
the significance of air pollution levels in their communi-
ties. For example, the color orange means that conditions
are "unhealthy for sensitive groups"; the color red means
that conditions may be "unhealthy" for everyone, and so
on. You may see these colors when the AQI is reported
in the newspaper or on television, or on your state or
local air pollution agency's web site. The colors can help
you rapidly determine whether air pollutants are reaching
unhealthy levels in your area.
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AIR QUALITY INDEX
How is a community*s MIS Gaiouiated?
Air quality is measured by networks of monitors that
record the concentrations of the major pollutants at
more than a thousand locations across the country each
day. These raw measurements are then converted into
AQI values using standard formulas developed by EPA.
An AQI value is calculated for each of the individual
pollutants_in an area (ground-level ozone, paniculate
matter, carbon monoxide, sulfur dioxide, and nitrogen
dioxide). Finally, the highest of the AQI values for die
individual pollutants becomes the AQI value for that
day. For example, if on July 12 a certain area had AQI
values of 90 for ozone and 88 for sulfur dioxide, the AQI
value would be 90 for the pollutant ozone on that day.
Children active outdoors can be sensitive to some air pollutants.
and how is ihe AQi reported to She public?
In large metropolitan areas (more than 350,000 people),
state and local agencies are required to report the AQI
to the public daily. When the AQI is above 100, they
must also report which groups (e.g., children, people
with asthma or heart disease) may be sensitive to the
specific pollutant. If two or more pollutants have AQI
values above 100 on a given day, agencies will report
all the groups that are sensitive to those pollutants.
Although it is not required, many smaller communities
also report the AQI as a public health service.
Many metropolitan areas also report an AQI forecast that
allows local residents to plan their activities to protect
their health.
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AIR QUALITY INDEX
The AQI is a national index, so the values and colors
used to show local air quality and the associated level
of health concern will be the same everywhere you go in
the U.S. Look for the AQI to be reported in your local
newspaper, on television and radio, on the Internet, and
on state and local telephone hotlines.
B AQi in the Newspaper
Newspapers may use different formats to report die AQI.
Here is one example:
Pollutant Ozone
Today's Forecast 130
Quality Unhealthy for
Sensitive Groups
Children and people with
asthma are the groups
most at risk
• AQI in Television and Radio Weather Reports
Your local television or radio weathercasters may use
the AQI to provide information about air quality in
your area. Here's the type of report you might hear:
The Air ^Quality Index today was 160, a code red day
Air quality was. unhealthy due to ozone. Hot, sunny
weather and stagnant air caused ozone in Center City
to me to unhealthy levels. Children and people with
" / •* — r " f r
». asfhmd dre. the groups- most at risk
You might also hear your weathercasters use the AQI
to forecast air quality levels for the coming day. They
may provide suggestions about how to protect your
health when the air is unhealthy to breathe:
Tomorrow, the AQI for Center-City. is. predicted to .•
be betwee^i 160 and 170, a code'yed day. This means
that air pollution will be at unhealthy''levels. The
combination of cold winter air and morning rush-hour
traffic will cause carbon monoxide to rise to. unhealthy
levels. People with heart disease should plan to limit
moderate exertion and avoid sources of carbon
monoxide, such as heavy traffic.
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AIR QUALITY INDEX
a AQI on the Internet
EPAs AirNow web site (www.epa.gov/airnow) contains
general information about air pollution plus real-time and
forecast data for ground-level ozone. The web site also
contains facts about the health and environmental effects
of air pollution, steps you can take to protect your health
and reduce pollution, and links to state and local air pollu-
tion control agency web sites with local AQI information.
What are typieal AQI values "m most communities?
In many U.S. communities, AQI values are mostly below
100, with values greater than 100 occurring several times
a year. Several metropolitan areas in the United States
have more severe air pollution problems, and the AQI
in these areas may often exceed 100. AQI values higher
than 200 are very infrequent, and AQI values above
300 are extremely rare.
AQI values can vary significantly from one season to
another. In winter, for example, carbon monoxide is
likely to be the pollutant with the highest AQI values
in some areas, because cold weather makes it difficult
for car emission control systems to operate effectively.
In summer, ozone is the most significant air pollutant
in many communities, since it forms in the presence of
heat and sunlight.
AQI values also can vary depending on the time of day.
For example, ozone levels often peak in the afternoon,
while carbon monoxide is usually a problem during
morning or evening rush hours.
How oan 1 avoid heina exposed to harmful
air pollutants?
The following charts and text tell you where each pollu-
tant comes from, what health effects may occur for each
pollutant, and what you can do to protect your health.
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AIR QUALITY INDEX 7
Air Quality Index (AQI): Ozone
Good
Cautionary Statements
None
Unusually sensitive people
51 -100* Moderate should consider limiting prolonged
outdoor exertion.
"Generally, an AQI of 100 for ozone corresponds to an ozone level of 0.08 parts per million
(averaged over 8 hours).
What is ozone?
Ozone is an odorless, colorless gas composed of three
atoms of oxygen. Ozone occurs both in the Earth's
upper atmosphere and at ground level. Ozone can
be good or bad, depending on where it is found:
3 Good Ozone. Ozone occurs naturally in the Earth's
upper atmosphere—10 to 30 miles above the Earth's
surface—where it forms a protective layer that shields
us from the sun's harmful ultraviolet rays. This beneficial
ozone is gradually being destroyed by manmade
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8
AIR QUALITY INDEX
chemicals. An area where ozone has been significantly
depleted—for example, over the North or South pole—is
sometimes called a "hole in the ozone."
• Bad Ozone. In the Earths lower atmosphere, near
ground level, ozone is formed when pollutants emitted
by cars, power plants, industrial boilers, refineries,
chemical plants, and other sources react chemically in
the presence-of sunlight. Ozone at ground level is a
harmful pollutant. Ozone pollution is a concern during
the summer months, when the weather conditions
needed to form it—lots of sun, hot temperatures—
normally occur.
The risk of exposure to unhealthy levels of ozone is greatest during
summer months.
are the and who is at risk?
Roughly one out of every three people in the United
States is at a higher risk of experiencing ozone-related
health effects. Sensitive people include children and
adults who are active outdoors, people with respiratory
disease, such as asthima, and people with unusual sensi-
tivity to ozone.
H One group at high risk from ozone exposure is active
children because this group often spends a large part of >
the summer playing outdoors. However, people of all ages
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AIR QUALITY INDEX'
who are active outdoors are at increased risk because,
during physical activity, ozone penetrates deeper into
the parts of the lungs that are more vulnerable to injury.
H People widi respiratory diseases that make their lungs
more vulnerable to ozone may experience health effects
earlier and at lower ozone levels than less sensitive
individuals.
• Though scientists don't yet know why, some healthy
people experience health effects at more moderate levels
of outdoor exertion or at lower ozone levels than the
average person.
a Ozone can irritate the respiratory system, causing
coughing, throat irritation, and/or an uncomfortable
sensation in the chest.
H Ozone can reduce lung function and make it more
difficult to breathe deeply and vigorously. Breathing may
become more rapid and shallow than normal. This
reduction in lung function may limit a persons ability to
engage in vigorous outdoor activities.
• Ozone can aggravate asthma. "When ozone levels are
high more people with asthma have attacks diat require
a doctor's attention or die use of additional medication.
One reason this happens is that ozone makes people
more sensitive to allergens, die most common triggers of
asdima attacks.
m Ozone can increase susceptibility to respiratory
infections.
• Ozone can inflame and damage die lining of the lungs.
"Within a few days, die damaged cells are shed and
replaced—much like die skin peels after a sunburn.
Animal studies suggest that if this type of inflammation
happens repeatedly over a long time period (months,
years, a lifetime), lung tissue may become permanendy
scarred, resulting in less lung elasticity, permanent loss
of lung function, and a lower quality of life.
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10 AIR QUALITY INDEX
Air Qualify Index (AQI): Partieulate matter
0-50
Good
None
51 -100**
Moderate
None
None
* PM has two sets of cautionary statements, which correspond to the two sizes of PM that are measured:
• Particles up to 2.5 micrometers in diameter (PM2 s)
• Particles up to 10 micrometers in diameter (PM10)
** • An AQI of 100 for PM2 5 corresponds to a PMM level of 40 micrograms per cubic meter
(averaged over 24 hours).
• An AQI of 100 for PM10 corresponds to a PM10 level of 150 micrograms per cubic meter
(averaged over 24 hours).
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AIR QUALITY INDEX 11
What is paniculate matter?
The term "paniculate matter" (PM) includes both solid
particles and liquid droplets found in air. Many manmade
and natural sources emit PM direcdy or emit other pollu-
tants that react in the atmosphere to form PM. These solid
and liquid particles come in a wide range of sizes. Particles
less than. 10 micrometers in diameter tend to pose the
greatest health concern because they can be inhaled into
and accumulate in the respiratory system. Particles less than
2.5 micrometers in diameter are referred to as "fine" parti-
cles. Sources of fine particles include all types of combus-
tion (motor vehicles, power plants, wood burning, etc.) and
some industrial processes. Particles with diameters between
2.5 and 10 micrometers are referred to as "coarse." Sources
of coarse particles include crushing or grinding operations,
and dust from paved or unpayed roads.
Wfiat are the health effects and who is most at risk?
Both fine and coarse particles can accumulate in the
respiratory system and are associated with numerous
health effects. Coarse particles can aggravate respiratory
conditions such as asthma. Exposure to fine particles
is associated with several serious health effects, including
premature death. Adverse health effects have been associ-
ated with exposures to PM over both short periods (such
as a day) and longer periods (a year or more).
H "When exposed to PM, people with existing heart or
lung diseases—such as asthma, chronic obstructive
pulmonary disease, congestive heart disease, or ischemic
heart disease-—are at increased risk of premature death
or admission to hospitals or emergency rooms.
H The elderly also are sensitive to PM exposure. They are
at increased risk of admission to hospitals or emergency
rooms and premature death from heart or lung diseases.
H When exposed to PM, children and people with exist-
ing lung disease may not be able to breathe as deeply or
vigorously as they normally would, and they may experi-
ence symptoms such as coughing and shortness of breath.
a PM can increase susceptibility to respiratory infections
and can aggravate existing respiratory diseases, such as
-asthma and chronic bronchitis, causing more use of
medication and more doctor visits.
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12 AIR QUALITY INDEX
0-50
51 -100*
Good
Moderate
l\lone
None
* An AQI of 100 for carbon monoxide corresponds to a GO level of 9 parts per million
(averaged over 8 hours).
What is earbQii monoxide?
Carbon monoxide (CO) is an odorless, colorless gas.
It forms when the carbon in fuels does not completely
burn. Vehicle exhaust contributes roughly 60 percent of
all carbon monoxide emissions nationwide, and up to
95 percent in cities. Other sources include fuel combus-
tion in industrial processes and natural sources such as
wildfires. Carbon monoxide concentrations typically are
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AIR QUALITY INDEX 13
lighest during cold weather, because cold temperatures
[lake combustion less complete and cause inversions
tiat trap pollutants low to the ground.
ffliat are the health effects and who is most at risk?
"arbon monoxide enters the bloodstream through die
ings and binds chemically to hemoglobin, the substance
i blood that carries oxygen to cells. In this way, carbon
lonoxide reduces the amount of oxygen reaching die
odys organs and tissues.
People with cardiovascular disease, such as angina,
re most at risk from carbon monoxide. These individu-
.s may experience chest pain and more cardiovascular
'mptoms if they are exposed to carbon monoxide,
articularly while exercising.
hide exhaust contributes roughly 60 percent of all carbon
moxide emissions nationwide.
People with marginal or compromised cardiovascular
.d respiratory systems (for example, individuals with
ngestive heart failure, cerebrovascular disease, anemia,
ronic obstructive lung disease), and possibly fetuses
d young infants, may also be at greater risk from
rbon monoxide pollution.
.n healdiy individuals, exposure to higher levels of
rbon monoxide can affect mental alertness and vision.
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14 AIR QUALITY INDEX
Air Qualify Index (AQ1): Sulfur Dioxide (S8-)
Index Values
51 -100*
•Good . ..
Moderate
Cautionary
Statements
None
None
* An AQI of 100 for sulfur-dioxide corresponds to an S02 level of 0.14 parts per million
(averaged over 24 hours).
What is sulfur dioxide?
Sulfur dioxide (SO2), a colorless, reactive gas; is produced
during the burning of sulfur-containing fuels such as coal
and oil, during metal smelting, and by odier industrial
processes. Major sources include power plants and indus-
trial boilers. Generally, the highest concentrations of sul-
fur dioxide are found near large industrial sources.
What are the heall effeols and who is most at risk?
B Children and adults with asthma who are active out-
doors are most vulnerable to the health effects of sulfur
dioxide. The primary effect they experience, even with
brief exposure, is a narrowing of the airways (called
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AIR QUALITY INDEX 15
bronchoconstriction), which may cause symptoms such
as wheezing, chest tightness, and shortness of breath.
Symptoms increase as sulfur dioxide concentrations
and/or breathing rates increase. When exposure ceases,
lung function typically returns to normal within an hour.
Children and adults with asthma who are active outdoors are most
.vulnerable to the health effects of sulfur dioxide.
H At very high levels, sulfur dioxide may cause wheezing,
chest tightness, and shortness of breath in people who
do not have asthma.
B Long-term exposure to both sulfur dioxide and fine
particles can cause respiratory illness, alter the lung's
defense mechanisms, and aggravate existing cardiovascu-
lar disease. People who may be most susceptible to these
effects include individuals with cardiovascular disease or
chronic lung disease, as well as children and die elderly.
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16 AIR QUALITY INDEX
51 -100
tHSaltnlfcanMrnSliSli^lSipmintMi
:.v::6ood ':',.-;...--..'''' Note
Moderate None
* Short-term health effects for nitrogen dioxide do not occur until AQI values are above 200;
therefore, the AQI is not calculated below 201 for N02. An AQI of 201 for N02 corresponds
to an N02 level of 0.65 parts per million (averaged over 24 hours).
What is nitrogen dioxide?
Nitrogen dioxide (NO2) is a reddish brown, highly reac-
tive gas formed when another pollutant (nitric oxide)
combines with oxygen in the atmosphere. Once it has
formed, nitrogen dioxide reacts with other pollutants
(volatile organic compounds). Eventually these reactions
result in die formation of ground-level ozone. Major
sources include automobiles and power plants,
What are the health effects and who is most at risk?
H In children and adults with respiratory disease, such as
asthma, nitrogen dioxide can cause respiratory symptoms
such as coughing, wheezing, and shortness of breath. Even
short exposures to nitrogen dioxide affect lung function.
• In children, short-term exposure can increase the risk
of respiratory illness.
• Animal studies suggest that long-term exposure to nitrogen
dioxide may increase susceptibility to respiratory infection
and may cause permanent structural changes in the lungs.
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For more information on air quality in your area,
visit EPA's AirNow web site at http://www.epa.gov/airnow
or call EPA's Office of Air and Radiation at (202) 564-7400.
For technical information on reporting the AQI,
see EPA's publication Guideline for Reporting of Daily
Air Quality—Air Quality Index (AQI), EPA-454/R-99-010,
at http://www.epa.gov/airnow/publications.html.
The focus of the AQI is on outdoor air quality.
For information on indoor air quality, contact EPA's Indoor Air
Quality Information Clearinghouse at (800) 438-4318.
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