United States
Environmental Protection
Agency
Air and Radiation
Washington, DC 20460
EPA-452/K-99-001
July 1999
http://www.epa.gov/oar/oaqps
&EPA Smog—Who Does It Hurt?
What You Need to Know About
Ozone and Your Health
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Who Does It Hurt?
What You Need to Know About Ozone and Your Health
On a hot, smoggy summer 'day,
__ •
have you ever wondered: Is the air safe to breathe?
Should I be concerned about going outside?
In fact, breathing smoggy air can
be hazardous because smog contains
ozone, a pollutant that can harm our
health when there are elevated levels
in the air we breathe. This publication
will tell you what kinds of health
effects ozone can cause, when you
should be concerned, and what you
can do to avoid dangerous exposures.
What is ozone?
Ozone is an odorless, colorless gas
composed of three atoms of oxygen.
Ozone occurs both in the Earths
upper atmosphere and at ground level.
Ozone can be good or bad, depending
on where it is found:
• Good Ozone. Ozone occurs natural-
ly 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 "good"
ozone is gradually being destroyed by
manmade chemicals. An area where
ozone has been most significantly
depleted—for example, over the
North or South pole—is sometimes
called a "hole in the ozone."
• 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.
The booklet Ozone: Good Up High,
Bad Nearby, which can be found on
the web at http://www.epa.gov/oar/
oaqps/gooduphigh, contains addition-
al information about both good and
bad ozone.
This publication, Smog—Who Does It
Hun?, focuses on bad ozone—that is,
ozone that occurs at ground level and
can affect the health of people who
breathe it.
Ozone, when it occurs
at ground level, presents
a serious air quality problem
in many parts of the United
States. When inhaled-
even at very low levels-
ozone can cause a number
of respiratory health effects.
Smog-Who Does It Hurt?
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Children and adults of all ages who
are active outdoors are at risk from
ozone exposure.
That depends on who you are and
how much ozone is in the air. Most
people only have to worry about
ozone exposure when ground-level
concentrations reach high levels.
In many U.S. communities, this can
happen frequently during the summer
months. In general, as ground-level
ozone concentrations increase, more
and more people experience health
effects, the effects become more seri-
ous, and more people are admitted to
the hospital for respiratory problems.
When ozone levels are very high,
everyone should be concerned about
ozone exposure.
Scientists have found that about
one out of every three people in the
United States is at a higher risk of
experiencing ozone-related health
effects (see box on page 3). If you
are a member of a "sensitive group,"
you should pay special attention to
ozone levels in your area. This publica-
tion describes several tools that the
U.S. Environmental Protection Agency
(EPA), in partnership with State and
local agencies, has developed to inform
the public about local ozone levels.
These tools provide the information
you need to decide whether ozone
levels on any particular day may be
harmful to you. When ozone concen-
trations reach unhealthy levels, you
can take simple precautions (described
on page 6 in "What can I do to avoid
unhealthy exposure to ozone?") to
protect your health.
Scientists have been studying the
effects of ozone on human health for
many years. So far, they have found
that ozone can cause several types of
short-term health effects in the lungs:
•• Ozone can irritate the respir-
atory system. When this happens,
you might start coughing, feel an irri-
tation in your throat, and/or experi-
ence an uncomfortable sensation in
your chest. These symptoms can last
for a few hours after ozone exposure
and may even become painful.
• Ozone can reduce lung function.
When scientists refer to "lung func-
tion," they mean the volume of air that
you draw in when you take a full breath
and the speed at which you are able to
blow it out. Ozone can 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 uncomfort-
able. If you are exercising or working
outdoors, you may notice that you are
taking more rapid and shallow breaths
than normal. Reduced lung function
can be a particular problem for out-
door workers, competitive athletes, and
other people who exercise outdoors.
• Ozone can aggravate asthma.
When ozone levels are high, more
asthmatics have asthma attacks that
require a doctor's attention or the use
of additional medication. One reason
this happens is that ozone makes peo-
ple more sensitive to allergens, which
are the most common triggers for
asthma attacks. (Allergens come from
dust mites, cockroaches, pets, fungus,
and pollen.) Also, asthmatics are more
severely affected by the reduced lung
function and irritation that ozone
causes in the respiratory system.
It
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• Ozone can inflame and damage
the lining of the lung. Some scientists
have compared ozones effect on the
lining of the lung to the effect of sun-
burn on the skin. Ozone damages the
cells that line the air spaces in the lung.
Within a few days, the damaged cells
are replaced and the old cells are shed—
much in the way that skin peels after
a sunburn. If this kind of damage
occurs repeatedly, the lung may change
permanently in a way that could cause
long-term health effects and a lower
quality of life.
• Scientists suspect that ozone may
have other effects on people's health.
Ozone may aggravate chronic lung
diseases, such as emphysema and bron-
chitis. Also, studies in animals suggest
that ozone may reduce the immune
systems ability to fight off bacterial
infections in the respiratory system.
Most of these effects are considered
to be short-term effects because they
eventually cease once the individual
is no longer exposed to elevated levels
of ozone. However, scientists are
concerned that repeated short-term
V, IH.I Is at rislc from
Four groups of people, described below, are particularly sensitive
to ozone. These groups become sensitive to ozone when they are active
outdoors, because physical activity (such as jogging or outdoor work)
causes people to breathe faster and more deeply. During activity, ozone
penetrates deeper into the parts of the lungs that are more vulnerable to
injury. Sensitive groups include:
• Children. Active children are the group at highest risk from ozone expo-
sure. Such children often spend a large part of their summer vacation
outdoors, engaged in vigorous activities either in their neighborhood or at
summer camp. Children are also more likely to have asthma or other
respiratory illnesses. Asthma is the most common chronic disease for chil-
dren and may be aggravated by ozone exposure.
• Adults who are active outdoors. Healthy adults of all ages who exer-
cise or work vigorously outdoors are considered a "sensitive group"
because they have a higher level of exposure to ozone than people who
are less active outdoors.
• People with respiratory diseases, such as asthma. There is no evi-
dence that ozone causes asthma or other chronic respiratory disease, but
these diseases do make the lungs more vulnerable to the effects of ozone.
Thus, individuals with these conditions will generally experience the
effects of ozone earlier and at lower levels than less sensitive individuals.
• People with unusual susceptibility to ozone. Scientists don't yet
know why, but some healthy people are simply more sensitive to ozone
than others. These individuals may experience more health effects from
ozone exposure than the average person.
Scientists have studied other groups to find out whether they are at
increased risk from ozone. So far there is little evidence to suggest that
either the elderly or people with heart disease have heightened sensitivity
to ozone. However, like other adults, elderly people will be at higher risk
from ozone exposure if they suffer from respiratory disease, are active
outdoors, or are unusually susceptible to ozone as described above.
This photo shows a healthy lung air-
way (top) and an inflamed lung airway
(bottom). Ozone can inflame the
lung's lining, and repeated episodes
of inflammation may cause permanent
changes in the lung.
Smog-Who Does It Hurt?
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A volunteer in an ozone
research study breathes into
a spirometer—a device that
measures lung function.
EPA has gathered a great deal of information about the health effects of ozone.
This information comes from a number of sources, including animal research, stud-
ies that compare health statistics and ozone levels within communities, and con-
trolled testing of human volunteers to determine how ozone affects lung function.
In these studies, volunteers are exposed to ozone in specially designed chambers
where their responses can be carefully measured. Volunteers are prescreened in
medical examinations to determine their health status, and they are never exposed
to ozone levels that exceed those found in major cities on a very smoggy day.
Though our understanding of ozone's effects has increased substantially in recent
years, many important questions still remain to be investigated. For example, does
repeated short-term exposure to high levels of ozone cause permanent lung dam-
age? Does repeated exposure during childhood to high levels of ozone cause
reduced lung function in adults? Scientists are continuing to study these and other
questions to gain a better understanding of ozone's effects.
damage from ozone exposure may
permanently injure the lung. For
example, repeated ozone impacts on
the developing lungs of children may
lead to reduced lung function as adults.
Also, ozone exposure may speed up the
decline in lung function that occurs as
a natural result of the aging process.
Research is underway to help us better
understand the possible long-term
effects of ozone exposure.
H
Often, people exposed to ozone experi-
ence recognizable symptoms, including
coughing, irritation in the airways,
rapid or shallow breathing, and dis-
comfort when breathing or general
discomfort in the chest. People with
asthma may experience asthma attacks.
When ozone levels are higher than
normal, any of these symptoms may
indicate that you should minimize the
time spent outdoors, or at least reduce
your activity level, to protect your
health until ozone levels decline.
Ozone damage also can occur without
any noticeable signs. Sometimes there
are no symptoms, or sometimes they
are too subtle to notice. People who
live in areas where ozone levels are fre-
quently high may find that their initial
symptoms of ozone exposure go away
over time—particularly when exposure
to high ozone levels continues for sever-
al days. This does not mean that they
have developed resistance to ozone.
In fact, scientists have found that 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
precautions to minimize exposure even
when you don't feel obvious symptoms.
ie , •: ; ..-.- :,
•i; i £•'/• -' ''.«*'•:*
EPA and State and local air agencies
have developed a number of tools
to provide people with information
on local ozone levels, their potential
health effects, and suggested activities
for reducing ozone exposure.
Air Quality Index. EPA has devel-
oped the Air Quality Index, or AQI,
(formerly known as the Pollutant
Standards Index) for reporting the
levels of ozone and other common air
pollutants. The index makes it easier
for the public to understand the health
significance of air pollution levels.
Air quality is measured by a nation-
wide monitoring system that records
concentrations of ozone and several
other air pollutants at more than a
thousand locations across the country.
Does It
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EPA "translates" the pollutant concen-
trations to the standard AQI index,
which ranges from 0 to 500. The high-
er the AQI value for a pollutant, the
greater the danger. An AQI value of
100 usually corresponds to the national
ambient air quality standard (NAAQS)
for the pollutant. These standards are
established by EPA under the Clean
Air Act to protect public health and
the environment.
The AQI scale has been divided into
distinct categories, each corresponding
to a different level of health concern.
In the table below, the AQI ranges are
shown in the middle column and the
associated air quality descriptors are
shown in the right column. The left col-
umn shows the ozone concentrations,
measured in parts per million (ppm),
that correspond to each category.
Though the AQI scale extends to 500,
levels above 300 rarely occur in the
United States. This publication and
most other references to the AQI do
not list health effects and cautionary
statements for levels above 300. If
ozone levels above 300 should ever
occur, everyone should avoid physical
exertion outdoors.
When pollutant levels are high, states
are required to report the AQI in large
metropolitan areas (populations over
350,000) of the United States. You
may see the AQI for ozone reported
in your newspaper, or your local televi-
sion or radio weathercasters may use
the AQI to provide information about
ozone in your area. Here's
the type of report you
might hear:
The Air Quality Index
today was 160. Air quali-
ty was unhealthy due to
ozone. Hot, sunny weather
and stagnant air caused
ozone in Center City to
rise to unhealthy levels.
AQI Colors. To make it
easier for the public to
quickly understand the
air quality in their com-
munities, EPA has
assigned a specific color
to each AQI category.
You will see these colors
when the AQI is reported
in a color format—such as
in a color-print newspaper, on televi-
sion broadcasts, or on your State or
local air pollution agency's web site.
This color scheme can help you quick-
ly determine whether air pollutants are
reaching unhealthy levels in your area.
For example, the color orange means
that conditions are "unhealthy for
sensitive groups," the color red means
that conditions are "unhealthy" for
everyone, and so on.
Ozone Maps. In many areas of the
country, measurements of ozone con-
centrations are converted into color
contours of the AQI categories (green,
yellow, orange, red, and purple, shown
below) and displayed on a map (see
example above) to show ozone levels
This map shows ozone levels in the
eastern United States on August 24,
1998. Ozone maps are updated several
times daily to show how ozone levels
change throughout the day.
Ozone Concentration (ppm) I Air Quality Index Values
(8-hour average, unless noted) I
Air Quality Descriptor
0.0 to 0.064
0.065 to 0.084
0.085 to 0.104
0.105 to 0.124
0.125 (8-hr.) to 0.404 (1-hr.)
OtoSO
51 to 100
101 to 150
151 to 200
201 to 300
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Smog-Who Does It Hurt?
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In
are your
hy the
you are and
the the
in,
in the local area. The map is updated
throughout the day and shows how
ozone builds during hot summer days.
In some areas, ozone maps are used
to show a forecast of ozone levels for
the next day. Once you understand
the color scheme, you can use the maps
to quickly determine whether ozone
concentrations are reaching unhealthy
levels in your area. Ozone maps appear
on some televised weather broadcasts
and are also available from EPA's web
site at http://www.epa.gov/airnow.
You can take a number of steps. The
chart on page 7 tells you what types
of health effects may occur at specific
ozone concentrations and what you can
do to avoid them. If you are a parent,
keep in mind that your children are
likely to be at higher risk, particularly
if they are active outdoors. You may
therefore want to pay special attention
to the guidance for sensitive groups.
In general, when ozone levels are
elevated, your chances of being
affected by ozone increase the longer
you are active outdoors and the more
strenuous the activity you engage in.
Scientific studies show that:
« At ozone levels above 0.12 ppm,
heavy outdoor exertion for short peri-
ods of time (1 to 3 hours) can increase
your risk of experiencing respiratory
symptoms and reduced lung function.
« At ozone levels between 0.08 and
0.12 ppm, even moderate outdoor
exertion for longer periods of time
(4 to 8 hours) can increase your risk
of experiencing ozone-related effects.
EPA recommends limiting outdoor
activities as ozone levels rise to
unhealthy levels. You can limit the
lies lite i§ do will
Exercise and outdoor activities can play an important role in maintaining
good health. Physical exertion helps build up strength in the heart and
lungs. But exerting yourself outdoors can actually increase your chances
of experiencing health effects when ozone concentrations are at unhealthy
levels. Why is this true? Think of it this way: Exertion generally causes you
to breathe harder and faster. When this happens, more ozone is taken into
your lungs, and ozone reaches tissues that are susceptible to injury.
Research has shown that respiratory effects are observed at lower ozone
concentrations if either the level or duration of exertion is increased. This
is why EPA recommends decreasing the level or duration of exertion to
avoid ozone health effects.
Examples of typical daily activities that involve moderate exertion include
climbing stairs, light jogging, easy cycling, playing tennis or baseball, and
stacking firewood. Outdoor occupational activities such as simple con-
struction work, pushing a wheelbarrow with a load, using a sledgehammer,
or digging in your garden, would also involve moderate exertion. Activities
that involve heavy exertion include vigorous running or cycling, playing
basketball or soccer, chopping wood, and heavy manual labor. Because fit-
ness levels vary widely among individuals, what is moderate 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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Health Effects and Protective Actions for Specific Ozone Ranges
Ozone Level I Health Effects and Protective Actions
Good
Moderate
Unhealthy
for Sensitive
Groups
Very
Unhealthy
What are the possible health effects?
• No health effects are expected.
What are the possible health effects?
• Unusually sensitive individuals may experience respiratory effects from prolonged exposure to
ozone during outdoor exertion.
What can I do to protect my health?
• When ozone levels are in the "moderate" range, consider limiting prolonged outdoor exertion if you
are unusually sensitive to ozone.
What are the possible health effects?
• If you are a member of a sensitive group,1 you may experience respiratory symptoms (such as coughing or
pain when taking a deep breath) and reduced lung function, which can cause some breathing discomfort.
What can I do to protect my health?
• If you are a member of a sensitive group,1 limit prolonged outdoor exertion. In general, you can
protect your health by reducing how long or how strenuously you exert yourself outdoors and by
planning outdoor activities when ozone levels are lower (usually in the early morning or evening).
• You can check with your State air agency to find out about current or predicted ozone levels in your
location. This information on ozone levels is available on the Internet at http://www.epa.gov/airnow.
What are the possible health effects?
• If you are a member of a sensitive group,1 you have a higher chance of experiencing respiratory
symptoms (such as aggravated cough or pain when taking a deep breath), and reduced lung •
tion, which can cause some breathing difficulty.
• At this level, anyone could experience respiratory effects.
What can I do to protect my health?
• If you are a member of a sensitive group,1 avoid prolonged outdoor exertion. Everyone else—
especially children—should limit prolonged outdoor exertion.
• Plan outdoor activities when ozone levels are lower (usually in the early morning or evening).
• You can check with your State air agency to find out about current or predicted ozone levels in your
location. This information on ozone levels is available on the Internet at http://www.epa.gov/airnow.
What are the possible health effects?
• Members of sensitive groups1 will likely experience increasingly severe respiratory symptoms and
impaired breathing.
• Many healthy people in the general population engaged in moderate exertion will experience some
kind of effect. According to EPA estimates, approximately:
• Half will experience moderately reduced lung function.
• One-fifth will experience severely reduced lung function.
• 10 to 15 percent will experience moderate to severe respiratory symptoms (such as aggravated
cough and pain when taking a deep breath).
• People with asthma or other respiratory conditions will be more severely affected, leading some to
increase medication usage and seek medical attention at an emergency room or clinic.
What can I do to protect my health?
• If you are a member of a sensitive group,1 avoid outdoor activity altogether. Everyone else—especially
children—should limit outdoor exertion and avoid heavy exertion altogether.
• Check with your State air agency to find out about current or predicted ozone levels in your loca-
tion. This information on ozone levels is available on the Internet at http://www.epa.gov/airnow.
1 Members of sensitive groups include children who are active outdoors; adults involved in moderate or strenuous outdoor
activities; individuals with respiratory disease, such as asthma; and individuals with unusual susceptibility to ozone.
Smog-Who Does It Hurt?
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The best way to your
is to find out
are
in your area and take
to
you
feel
Motor vehicles are a major contributor to smog.
amount of time you are active outdoors
or your activity level. For example,
if you're involved in an activity that
requires heavy exertion, such as run-
ning or heavy manual labor (see box
on page 6), you can reduce the time
you spend on this activity or substitute
another activity that requires less exer-
tion (e.g., go for a walk rather than a
You can help reduce ozone levels by
walking, biking, carpooling, or using
public transportation as an alternative
to driving.
jog). In addition, you can plan outdoor
activities when ozone levels are lower,
usually in the early morning or evening.
Ground-level ozone is created when
certain pollutants, known as "ozone
precursors," react in heat and sunlight
to form ozone. Cars and other vehicles
are the largest source of ozone precur-
sors. Other important sources include
industrial facilities, power plants, gaso-
line-powered mowers, and evaporation
of cleaners, paints, and other chemicals.
We can all help reduce ozone levels by
taking the following steps:
Drive less. For example, instead of
using a car, you may want to walk,
use mass transit, or ride a bike.
• Carpool.
• Make sure your car is well-tuned.
« Take care not to spill gasoline when
you fill the tank of your car or lawn or
recreation equipment.
« Make sure that you tightly seal the
lids of chemical products—such as
solvents, garden chemicals, or house-
hold cleaners—to keep evaporation to
a minimum.
For more ideas about what you can do,
visit EPA's web site at http://www.epa.
gov/airnow/consumer.html.
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