A Guide to Air Quality and Your Health
Introduction
!["Local air quality is unhealthy today." "It's a code red air quality day for ozone." "Today's Air Quality Index is 105, which is unhealthy for sensitive groups."](quotes.gif)
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.
![An elderly couple jogging.](couple_jog.gif)
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 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.
How does the AQI work?
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.
Understanding the AQI
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:
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 |
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.
How is a community’s AQI calculated?
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 for the pollutant ozone on that day.
When and how is the AQI reported to the public?
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.
![A picture of kids rollerskating.](kids.gif)
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:
![Air Quality Index](aqi.gif)
- 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 (www.epa.gov/airnow)
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.
What are typical AQI values in most communities?
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.
How can I avoid being exposed to harmful air pollutants?
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 in this booklet 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.
Air
Quality Index (AQI): Ozone
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. |
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—6 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.”
- 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.
![A young girl playing in a sprinkler.](sprinkler.jpg)
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.
Air
Quality Index (AQI): Particle Pollution
0-50 |
Good |
None |
51-100* |
Moderate |
Unusually sensitive people
should consider reducing prolonged or heavy exertion. |
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. |
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.
Air Quality Index (AQI):
Carbon Monoxide (CO)
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. |
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. |
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.
- 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.
![A picture of cars driving along a highway.](cars.jpg)
Air Quality Index (AQI):
Sulfur Dioxide (SO2)
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. |
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.
- 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.
![A female student with an inhaler.](student.jpg)
- 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.
Where can I get more information?
For information on air quality in your area, visit EPA's
AIRNow web site at http://www.epa.gov/airnow/.
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 or visit http://www.epa.gov/iaq.
|