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A Guide to Air Quality and Your Health |
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What
is the Air Quality Index (AQI)?
How
does the AQI work?
How
is a community's AQI calculated?
When
and how is the AQI reported to the public?
What
are typical AQI values in most communities?
How
can I avoid being exposed to harmful air pollutants?
Air
Quality Index (AQI): Ozone
Air
Quality Index (AQI): Particle Pollution
Air
Quality Index (AQI): Carbon Monoxide (CO)
Air
Quality Index (AQI): Sulfur Dioxide (SO2)
Where
can I get more information?
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Increasingly, radio, TV, and newspapers are providing information
like this to local communities. But what does it mean to you ...if
you are planning outdoor activities that day? ...if you have children
who play outdoors? ...if you are an older adult? ...if you have
asthma? This booklet will help you understand what you can do to
protect yourself from air pollution.
Local air quality affects how you 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 easy to understand as the weather forecast.
A key tool in this effort is the Air Quality Index, or AQI. EPA
and local officials use the AQI to provide you with simple information
on local air quality, the health concerns for different levels of
air pollution, and how you can protect your health when pollutants
reach unhealthy levels.
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What is the Air Quality Index (AQI)? |
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Air quality directly affects our quality
of life.
The AQI is an index for reporting daily air quality. It tells you
how clean or polluted your air is, and what associated health effects
might be a concern for you. The AQI focuses on health effects you
may experience within a few hours or days after breathing polluted
air. EPA calculates the AQI for five major air pollutants regulated
by the Clean Air Act: ground-level ozone, particle pollution (also
known as particulate matter), carbon monoxide, sulfur dioxide, and
nitrogen dioxide. For each of these pollutants, EPA has established
national air quality standards to protect public health.
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How does the AQI work? |
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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 concern.
For example, an AQI value of 50 represents good air quality with little
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. 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, then for everyone
as AQI values get higher. |
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The purpose of the AQI is to help you understand what local air
quality means to your health. To make it easier to understand, the
AQI is divided into six categories:
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When the AQI
is in this range: |
...air quality conditions
are: |
...as symbolized
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 |
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Each category corresponds to a different level of health concern.
The six levels of health concern and what they mean are:
- "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.
- "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 people. For example, people who are unusually sensitive to
ozone may experience respiratory symptoms.
- "Unhealthy for Sensitive Groups" When AQI
values are between 101 and 150, members of sensitive groups may
experience health effects. This means they are likely to be affected
at lower levels than the general public. For example, people
with lung disease are at greater risk from exposure to ozone,
while people with either lung disease or heart disease are at
greater risk from exposure to particle pollution. The general
public is not likely to be affected when the AQI is in this range.
- "Unhealthy" Everyone may begin to experience
health effects when AQI values are between 151 and 200. Members
of sensitive groups may experience more serious 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
warnings of emergency conditions. The entire population is more
likely to be affected.
AQI colors
A specific color is assigned to each AQI category to make it easier
for you to understand quickly whether air pollution is reaching
unhealthy levels in your community. For example, the color orange
means that conditions are "unhealthy for sensitive groups," while
red means that conditions may be "unhealthy for everyone," and
so on.
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How is a community's AQI calculated? |
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Air quality is measured
by monitors that record the concentrations of the major pollutants
each day at more than a thousand locations across the country. These
raw measurements are then converted into AQI values using standard
formulas developed by EPA. An AQI value is calculated for each pollutant
in an area (ground-level ozone, particle pollution, carbon monoxide,
sulfur dioxide, and nitrogen dioxide). The highest AQI value for the
individual pollutants is 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 on that day.
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When and how is the AQI reported to the public? |
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In large cities (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, agencies must also report which groups, such as children
or 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 must report all the groups that are
sensitive to those pollutants. Many smaller communities also report
the AQI as a public health service.
Children active outdoors can be sensitive to some air pollutants.
Many cities also provide forecasts for the next day's AQI. These
forecasts help local residents protect their health by alerting
them to plan their strenuous activities for a time when air quality
is better.
The AQI is a national index, so the values and colors used to show
local air quality and the levels of health concern will be the same
everywhere you go in the United States. Look for the AQI to be reported
in your local newspaper, on television and radio, on the Internet,
and on many state and local telephone hotlines.
- AQI in the Newspaper
Newspapers in many U.S. cities, and some national newspapers,
carry AQI reports each day. Here is one example:
- AQI in Television and Radio Weather Reports
Many local television or radio weathercasters use the AQI to provide
air quality information in your area. Here's the type of report
you might hear:
Tomorrow will be a code red air quality day for
Center City. The cold winter air, morning traffic, and
wood smoke are expected to cause particle pollution to
rise to unhealthy levels. People with heart or lung disease,
older adults, and children should avoid strenuous activities. |
- AQI on the Internet
EPA's AIRNow
web site contains general information about air pollution plus
real-time and forecast air quality data. It also contains facts
about the health and environmental effects of air pollution, steps
you can take to protect your health and to reduce pollution, and
links to state and local air pollution agency web sites.
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What are typical AQI values in most communities? |
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In many U.S. communities, AQI values are usually below 100, with
values greater than 100 occurring just several times a year. Typically,
larger cities have more severe air pollution problems, and the AQI
in these areas may exceed 100 more often than in smaller cities.
AQI values higher than 200 are infrequent, and AQI values above
300 are extremely rare.
AQI values can vary from one season to another. In winter, for
example, carbon monoxide may be high in some areas because the cold
weather makes it difficult for car emission control systems to operate
effectively. In summer, ozone may be a significant air pollutant
because it forms in the presence of heat and sunlight. Particle
pollution can be elevated at any time of the year.
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. Particle
pollution can be high at any time of day.
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How can I avoid being exposed to harmful air pollutants? |
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The following AQI charts tell you how you can protect your health
from air pollution. Each chart contains cautionary language to help
you when air quality levels are unhealthy. In general, you can reduce
your risk by "reducing prolonged or heavy exertion." Prolonged exertion
is an activity that occurs over several hours and makes you breathe
slightly harder than normal. Reducing prolonged exertion could mean
reducing the time you spend on this type of activity. You can also
reduce your risk by cutting back on heavy exertion-more intense
activities that cause you to breathe hard. This might mean walking
instead of jogging, or jogging for half your usual time. Your breathing
rate is a guide to how hard you are exerting yourself. If you experience
any unusual coughing, chest discomfort, wheezing, or breathing difficulty,
you should reduce your activity level.
Charts are provided for four pollutants: ozone, particle pollution,
carbon monoxide, and sulfur dioxide. Another common pollutant, nitrogen
dioxide, can cause respiratory symptoms such as coughing, wheezing,
and shortness of breath in children and adults who have respiratory
diseases, such as asthma. The AQI for nitrogen dioxide is not included
here because nitrogen dioxide levels across the country have been
below the national air quality standard for the past several years.
Nitrogen dioxide levels are usually so low that they pose little
direct threat to human health. Nitrogen dioxide, however, is a concern
because it plays a significant role in the formation of ozone, particle
pollution, haze, and acid rain.
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Air Quality Index (AQI): Ozone |
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0-50 |
Good |
None |
51-100* |
Moderate |
Unusually sensitive
people should consider reducing prolonged or heavy exertion
outdoors. |
101-150 |
Unhealthy for Sensitive Groups |
Active children
and adults, and people with lung disease, such as asthma,
should reduce prolonged or heavy exertion outdoors. |
151-200 |
Unhealthy |
Active
children and adults, and people with lung disease, such
as asthma, should avoid prolonged or heavy exertion outdoors.
Everyone else, especially children, should reduce prolonged
or heavy exertion outdoors. |
201-300 |
Very Unhealthy |
Active
children and adults, and people with lung disease, such
as asthma, should avoid all outdoor exertion. Everyone else,
especially children, should avoid prolonged or heavy exertion
outdoors. |
301-500 |
Hazardous |
Everyone
should avoid all physical activity outdoors. |
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What is ozone?
Ozone is a 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:
- Good Ozone. Ozone occurs naturally in the Earth's
upper atmosphere, six 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 chemicals. An area where the protective "ozone
layer" has been significantly depleted, for example, over
the North or South pole, is sometimes called "the ozone hole."
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The risk of exposure to unhealthy levels
of ground-level ozone is the greatest during the summer months.
Bad Ozone. In the Earth's 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 air pollutant.
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 problems from ground-level ozone.
- One group at high risk is active children because they often
spend a large part of the summer playing outdoors.
- People of all ages 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.
- People with respiratory diseases, including asthma, that make
their lungs more vulnerable to ozone may experience health effects
earlier and at lower ozone levels than other people.
- Though scientists don't yet know why, some healthy people are
unusually sensitive to ozone. They may experience health effects
at more moderate levels of outdoor exertion or at lower ozone
levels than the average person.
- Ozone can irritate the respiratory system, causing coughing,
throat irritation, and/or an uncomfortable sensation in the chest.
- 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 may limit a person's ability to
engage in vigorous activities.
- Ozone can aggravate asthma. When ozone levels are high, more
people with asthma have attacks that require a doctor's attention
or use of medication. One reason this happens is that ozone makes
people more sensitive to allergens such as pets, pollen, and dust
mites, which are common triggers of asthma attacks.
- Ozone can increase susceptibility to respiratory infections.
- Ozone can inflame and damage the lining of the lungs. Within
a few days, the damaged cells are shed and replaced, much like
the skin peels after a sunburn. Studies suggest that if
this type of inflammation happens repeatedly over a long time
period (months, years, a lifetime), lung tissue may become permanently
scarred, resulting in permanent loss of lung function and a lower
quality of life.
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Air Quality Index (AQI): Particle Pollution |
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0-50 |
Good |
None |
51-100* |
Moderate |
Unusually sensitive
people should consider reducing prolonged or heavy exertion.
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101-150 |
Unhealthy for Sensitive Groups |
People with heart
or lung disease, older adults, and children should reduce
prolonged or heavy exertion. |
151-200 |
Unhealthy |
People
with heart or lung disease, older adults, and children should
avoid prolonged or heavy exertion. Everyone else should
reduce prolonged or heavy exertion. |
201-300 |
Very Unhealthy |
People
with heart or lung disease, older adults, and children should
avoid all physical activity outdoors. Everyone else should
avoid prolonged or heavy exertion. |
301-500 |
Hazardous |
People
with heart or lung disease, older adults, and children should
remain indoors and keep activity levels low. Everyone else
should avoid all physical activity outdoors. |
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What is particle
pollution?
Particle pollution (also known as "particulate matter") in the
air includes a mixture of solids and liquid droplets. Some particles
are emitted directly; others are formed in the atmosphere when other
pollutants react. Particles come in a wide range of sizes. Those
less than 10 micrometers in diameter are so small that they can
get into the lungs, potentially causing serious health problems.
Ten micrometers is smaller than the width of a single human hair.
- Fine particles. Particles less than 2.5 micrometers in
diameter are called "fine" particles. These particles are so small
they can be detected only with an electron microscope. Sources
of fine particles include all types of combustion, including motor
vehicles, power plants, residential wood burning, forest fires,
agricultural burning, and some industrial processes.
- Coarse dust particles. Particles between 2.5 and 10 micrometers
in diameter are referred to as "coarse." Sources of coarse particles
include crushing or grinding operations, and dust stirred up by
vehicles traveling on roads.
What are the health effects and who is most at risk?
Particles smaller than 10 micrometers in diameter can cause or
aggravate a number of health problems and have been linked with
illnesses and deaths from heart or lung diseases. These effects
have been associated with both short-term exposures (usually over
a 24-hour period, but possibly as short as one hour) and long-term
exposures (years).
- Sensitive groups for particle pollution include people with
heart or lung disease, older adults (who may have undiagnosed
heart or lung disease), and children.
- People with heart or lung diseases, such as congestive heart
failure, coronary artery disease, asthma, or chronic obstructive
pulmonary disease, and older adults are more likely to visit emergency
rooms, be admitted to hospitals, or in some cases, even die. When
exposed to particle pollution, people with heart disease may experience
chest pain, palpitations, shortness of breath, and fatigue. Particle
pollution has also been associated with cardiac arrhythmias and
heart attacks.
- When exposed to particles, people with existing lung disease
may not be able to breathe as deeply or vigorously as they normally
would. They may experience symptoms such as coughing and shortness
of breath. Healthy people also may experience these effects, although
they are unlikely to experience more serious effects.
- Particle pollution also 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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Air Quality Index (AQI): Carbon Monoxide (CO) |
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0-50 |
Good |
None |
51-100* |
Moderate |
None |
101-150 |
Unhealthy for Sensitive Groups |
People with heart
disease, such as angina, should reduce heavy exertion and
avoid sources of CO, such as heavy traffic. |
151-200 |
Unhealthy |
People
with heart disease, such as angina, should reduce moderate
exertion and avoid sources of CO, such as heavy traffic.
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201-300 |
Very Unhealthy |
People
with heart disease, such as angina, should avoid exertion
and sources of CO, such as heavy traffic. |
301-500 |
Hazardous |
People
with heart disease, such as angina, should avoid exertion
and sources of CO, such as heavy traffic. Everyone else
should reduce heavy exertion. |
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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 levels typically are highest during cold weather, because
cold temperatures make combustion less complete and cause inversions
that trap pollutants close to the ground.
What are the health effects and who is most at risk?
Carbon monoxide enters the bloodstream through the lungs and binds
to hemoglobin, the substance in blood that carries oxygen to cells.
It actually reduces the amount of oxygen reaching the body's organs
and tissues.
- People with cardiovascular disease, such as angina, are most
at risk. They may experience chest pain and other cardiovascular
symptoms if they are exposed to carbon monoxide, particularly
while exercising.
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Vehicle exhaust contributes roughly 60
percent of all of the carbon monoxide emissions nationwide
People with marginal or compromised cardiovascular and respiratory
systems (for example, individuals with congestive heart failure,
cerebrovascular disease, anemia, chronic obstructive lung disease),
and possibly young infants and fetuses, also may be at greater
risk from carbon monoxide pollution.
- In healthy individuals, exposure to higher levels of carbon
monoxide can affect mental alertness and vision.
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Air Quality Index (AQI): Sulfur Dioxide (SO2) |
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0-50 |
Good |
None |
51-100* |
Moderate |
None |
101-150 |
Unhealthy for Sensitive Groups |
People with asthma
should consider reducing exertion outdoors. |
151-200 |
Unhealthy |
Children,
asthmatics, and people with heart or lung disease should
reduce exertion outdoors. |
201-300 |
Very Unhealthy |
Children,
asthmatics, and people with heart or lung disease should
avoid outdoor exertion. Everyone else should reduce exertion
outdoors. |
301-500 |
Hazardous |
Children,
asthmatics, and people with heart or lung disease should
remain indoors. Everyone else should avoid exertion outdoors.
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What is sulfur
dioxide?
Sulfur dioxide (SO2), a colorless, reactive gas, is
produced when sulfur-containing fuels such as coal and oil are burned.
Major sources include power plants and industrial boilers. Generally,
the highest levels of sulfur dioxide are near large industrial complexes.
What are the health effects and who is most at risk?
Sulfur dioxide is an irritant gas that is removed by the nasal
passages. Moderate activity levels that trigger mouth breathing,
such as a brisk walk, are needed for sulfur dioxide to cause health
effects.
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Children and adults with asthma who are
active outdoors are most vulnerable to the health effects of
sulfur dioxide.
People with asthma who are physically active outdoors are most
likely to experience the health effects of sulfur dioxide. The
main effect, even with brief exposure, is a narrowing of the airways
(called bronchoconstriction). This may cause wheezing, chest tightness,
and shortness of breath. Symptoms increase as sulfur dioxide levels
and/or breathing rates increase. When exposure to sulfur dioxide
ceases, lung function typically returns to normal within an hour.
- At very high levels, sulfur dioxide may cause wheezing, chest
tightness, and shortness of breath even in healthy people who
do not have asthma.
- Long-term exposure to sulfur dioxide can cause respiratory illness,
alter the lung's defense mechanisms, and aggravate existing cardiovascular
disease. People with cardiovascular disease or chronic lung disease,
as well as children and older adults, may be most susceptible
to these effects.
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Where can I get more information? |
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For information on air quality in your area, visit EPA's AIRNow
web site.
For information on programs under way to improve air quality, visit
www.epa.gov/air.
The AQI focuses on outdoor air quality. For information on indoor
air quality, contact EPA's Indoor
Air Quality Information Hotline at (800) 438-4318.
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Adapted from EPA's
Air Quality
Index, A Guide to Air Quality and Your Health, AIRNow
web site, August 24, 2004. |
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