2Printed on paper containing at least 

30% postconsumer recovered fiber.
Qpp

to-understand information on local air qualit

whether air pollution levels pose a health con

This booklet tells you about

the AQI and how it is used to

provide air quality information.

It also tells you about the possible health effects of major air

pollutants at various levels and

suggests actions you can take 

to protect your health when

pollutants in your area reach

unhealthy concentrations. 

What is the AQI?

The AQI is an index for

reporting daily air quality. It

tells you how clean or polluted

your air is, and what associated

health concerns you should be aware of. The 

es on health effects that can happen within a 

or days after breathing polluted air. EPA uses 

for five major air pollutants regulated by the 

Act: ground-level ozone, particulate matter, c

monoxide, sulfur dioxide, and nitrogen dioxi

of these pollutants, EPA has established natio

ity standards to protect against harmful healt

Air quality di

our quality o

“Today’s Air Quality 

Index is 105, which is

unhealthy for sensitive

groups.”

communities. But what does it mean to you

...if you plan to be outdoors that day? 

...if 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.
values are between 101 and 150, members of 

groups may experience health effects. The gen

is not likely to be affected when the AQI is in 

■ “Unhealthy” AQI values are between 151 a

Everyone may begin to experience health effe

Members of sensitive groups may experience 

ous health effects.

■ “Very Unhealthy” AQI values between 20

trigger a health alert, meaning everyone may 

more serious health effects.

■ “Hazardous” AQI values over 300 trigger 

ings of emergency conditions. The entire pop

more likely to be affected.

AQI colors

EPA has assigned a specific color to each AQ

to make it easier for people to understand qu

the significance of air pollution levels in their 

ties. For example, the color orange means tha

are “unhealthy for sensitive groups”; the color 

that conditions may be “unhealthy” for every

on. You may see these colors when the AQI i

in the newspaper or on television, or on your 

local air pollution agency’s web site. The colo

you rapidly determine whether air pollutants 

unhealthy levels in your area. 

Understanding the 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: 

Each category corresponds to a different level of health concern. For example, when the AQI for a pollutant is between

51 and 100, the health concern is “Moderate.” Here are the

six levels of health concern and what they mean:

■ “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.

Air Quality Index Levels of Health Concern Colors

(AQI) Values

When the AQI ...air quality conditions are: ...as symbolized 

is in this range: by this color:

0 to 50 Good Green

51 to 100 Moderate Yellow

101 to 150 Unhealthy for Sensitive Groups Orange

151 to 200 Unhealthy Red

201 to 300 Very Unhealthy Purple

301 to 500 Hazardous Maroon
When and how is the AQI reported to the 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.

■ AQI in Television and Radio Weather Re

Your local television or radio weathercasters m

the AQI to provide information about air qu

your area. Here’s the type of report you migh

The Air Quality Index today was 160, a cod

Air quality was unhealthy due to ozone. Hot

weather and stagnant air caused ozone in C

to rise to unhealthy levels. Children and peop

asthma are the groups most at risk.

You might also hear your weathercasters use t

to forecast air quality levels for the coming da

may provide suggestions about how to protec

health when the air is unhealthy to breathe:

Tomorrow, the AQI for Center City is predic

be between 160 and 170, a code red day. Th

that air pollution will be at unhealthy levels

combination of cold winter air and morning 

traffic will cause carbon monoxide to rise to 

levels. People with heart disease should plan 

moderate exertion and avoid sources of carbo

monoxide, such as heavy traffic.

Children active outdoors can be sensitive to some air pollutants.
y Qg

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 can I avoid being exposed to harmful 

air pollutants?

The following charts and text tell you where each pollutant comes from, what health effects may occur for each

pollutant, and what you can do to protect your health.

151 - 200

201 - 300

301 - 500

Unhealthy

Very Unhealthy

Hazardous

people with respirato

such as asthma, sh

prolonged outdoor exer

else, especially child

limit prolonged outdo

Active children and 

people with respirato

such as asthma, sho

outdoor exertion; eve

especially children, s

outdoor exert

Everyone shoul

all outdoor exe

*Generally, an AQI of 100 for ozone corresponds to an ozone level of 0.08 p

(averaged over 8 hours).

What is ozone?

Ozone is an odorless, colorless gas composed 

atoms of oxygen. Ozone occurs both in the E

upper atmosphere and at ground level. Ozon

be good or bad, depending on where it is fou

■ Good Ozone. Ozone occurs naturally in th

upper atmosphere—10 to 30 miles above the 

surface—where it forms a protective layer tha

us from the sun’s harmful ultraviolet rays. Th

ozone is gradually being destroyed by manma
sensation in the chest. 

■ Ozone can reduce lung function and make 

difficult to breathe deeply and vigorously. Bre

become more rapid and shallow than normal

reduction in lung function may limit a perso

engage in vigorous outdoor activities. 

■ Ozone can aggravate asthma. When ozone 

high more people with asthma have attacks th

a doctor’s attention or the use of additional m

One reason this happens is that ozone makes 

more sensitive to allergens, the most common 

asthma attacks. 

■ Ozone can increase susceptibility to respirat

infections. 

■ Ozone can inflame and damage the lining o

Within a few days, the damaged cells are shed 

replaced—much like the skin peels after a sun

Animal studies suggest that if this type of infl

happens repeatedly over a long time period (m

years, a lifetime), lung tissue may become per

scarred, resulting in less lung elasticity, perma

of lung function, and a lower quality of life.

What are the health effects and who is most 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 asthma, and people with unusual sensitivity to ozone. 

■ 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

The risk of exposure to unhealthy levels of ozone is greatest during

summer months.
and dust from paved or unpaved roads.

What are the health effects and who is m

Both fine and coarse particles can accumulate 

respiratory system and are associated with nu

health effects. Coarse particles can aggravate 

conditions such as asthma. Exposure to fine p

is associated with several serious health effects

premature death. Adverse health effects have 

ated with exposures to PM over both short p

as a day) and longer periods (a year or more)

■ When exposed to PM, people with existing 

lung diseases—such as asthma, chronic obstr

pulmonary disease, congestive heart disease, o

heart disease—are at increased risk of premat

or admission to hospitals or emergency room

■ The elderly also are sensitive to PM exposu

at increased risk of admission to hospitals or 

rooms and premature death from heart or lun

■ When exposed to PM, children and people 

ing lung disease may not be able to breathe as 

vigorously as they normally would, and they m

ence symptoms such as coughing and shortne

■ PM can increase susceptibility to respiratory 

and can aggravate existing respiratory diseases

asthma and chronic bronchitis, causing more 

medication and more doctor visits.

151 - 200

201 - 300

301 - 500

Unhealthy

Very

Unhealthy

Hazardous

People with 

respiratory or

heart disease,

the elderly, and

children should

avoid prolonged

exertion; everyone else should

limit prolonged

exertion.

People with 

respiratory or

heart disease,

the elderly, and

children should

avoid any outdoor activity;

everyone else

should avoid prolonged exertion.

Everyone should

avoid any outdoor

exertion; people

with respiratory

or heart disease,

the elderly, and

children should

remain indoors.

p

piratory disease,

such as asthma,

should avoid outdoor exertion;

everyone else,

especially the

elderly and children, should

limit prolonged

outdoor exertion.

People with respiratory disease,

such as asthma,

should avoid any

outdoor activity;

everyone else,

especially the elderly and children,

should limit outdoor exertion.

Everyone should

avoid any outdoor exertion;

people with respiratory disease,

such as asthma,

should remain

indoors.

* 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 (PM2.5)

• Particles up to 10 micrometers in diameter (PM10)

** • An AQI of 100 for PM2.5 corresponds to a PM2.5 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).
151 - 200

201 - 300

301 - 500

Unhealthy

Very Unhealthy

Hazardous

angina, should limit

moderate exertion and

avoid sources of CO,

such as heavy traffic.

People with cardiovascular disease, such as angina, should avoid exertion

and sources of CO, such

as heavy traffic.

People with cardiovascular disease, such as

angina, should avoid

exertion and sources of

CO, such as heavy traffic; everyone else should

limit heavy exertion.

■ People with marginal or compromised card

and respiratory systems (for example, individ

congestive heart failure, cerebrovascular disea

chronic obstructive lung disease), and possibl

and young infants, may also be at greater risk 

carbon monoxide pollution. 

■ In healthy individuals, exposure to higher l

carbon monoxide can affect mental alertness 

* An AQI of 100 for carbon monoxide corresponds to a CO level of 9 parts per million 

(averaged over 8 hours).

Vehicle exhaust contributes roughly 60 percent of all ca

monoxide emissions nationwide.

What is carbon 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 combustion in industrial processes and natural sources such as

wildfires. Carbon monoxide concentrations typically are
■ At very high levels, sulfur dioxide may caus

chest tightness, and shortness of breath in pe

do not have asthma.

■ Long-term exposure to both sulfur dioxide 

particles can cause respiratory illness, alter the 

defense mechanisms, and aggravate existing c

lar disease. People who may be most suscepti

effects include individuals with cardiovascula

chronic lung disease, as well as children and t

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 other industrial

processes. Major sources include power plants and industrial boilers. Generally, the highest concentrations of sulfur dioxide are found near large industrial sources.

What are the health effects and who is most at risk?

■ Children and adults with asthma who are active outdoors 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 

201 - 300

301 - 500

Very Unhealthy

Hazardous

Children, asthmatics,

and people with heart or

lung disease should

avoid outdoor exertion;

everyone else should

limit outdoor exertion.

Children, asthmatics,

and people with heart or

lung disease should

remain indoors; 

everyone else should

avoid outdoor exertion.

* An AQI of 100 for sulfur dioxide corresponds to an SO2 level of 0.14 parts per million 

(averaged over 24 hours).

Children and adults with asthma who are active outdoo

vulnerable to the health effects of sulfur dioxide.
What is nitrogen dioxide?

Nitrogen dioxide (NO2) is a reddish brown, highly reactive 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 the formation of ground-level ozone. Major

sources include automobiles and power plants. 

What are the health effects and who is most at risk?

■ 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.

301 - 500

Hazardous

respiratory disease,

such as asthma, should

limit moderate or heavy

outdoor exertion.

* 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 NO2

. An AQI of 201 for NO2 corresponds 

to an NO2 level of 0.65 parts per million (averaged over 24 hours).

For more information on air quality in your 

visit EPA’s AirNow web site at http://www.epa.g

or call EPA’s Office of Air and Radiation at (202) 

For technical information on reporting the 

see EPA’s publication Guideline for Reporting 

Air Quality—Air Quality Index (AQI), EPA-454/

at http://www.epa.gov/airnow/publications.

The focus of the AQI is on outdoor air qu

For information on indoor air quality, contact EPA

Quality Information Clearinghouse at (800) 43