Ozone and Your Health

Ozone, the main ingredient of smog, presents a serious air quality problem in many parts of the United States. Even at low levels, ozone can cause a number of respiratory effects. You can take simple steps, described in this pamphlet, to protect your health from ozone.

Smog
Ozone is the main ingredient of smog.

What is ozone?

Ozone is a gas that 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-10 to 30 miles above the Earth's surface-where it shields us from the sun's harmful ultraviolet rays.

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 pollution is a concern during the summer months when the weather conditions needed to form ground-level ozone-lots of sun, hot temperatures-normally occur.

Are you at risk from ground-level ozone?

Several groups of people are particularly sensitive to ozone-especially when they are active outdoors-because physical activity causes people to breathe faster and more deeply.

Active children are the group at highest risk from ozone exposure because they often spend a large part of the summer playing outdoors. Children are also more likely to have asthma, which may be aggravated by ozone exposure.

Active adults of all ages who exercise or work vigorously outdoors have a higher level of exposure to ozone than people who are less active.

People with asthma or other respiratory diseases that make the lungs more vulnerable to the effects of ozone will generally experience health effects earlier and at lower ozone levels than less sensitive individuals.

People with unusual susceptibility to ozone. Scientists don't yet know why, but some healthy people may experience health effects at more moderate levels of outdoor exertion or at lower ozone levels than the average person.

In general, as concentrations of ground-level ozone increase, more and more people experience health effects, the effects become more serious, and more people are admitted to the hospital for respiratory problems. When ozone levels are very high, everyone should be concerned about ozone exposure.

Basketball
Children and adults of all ages who are active outdoors are at risk from ozone exposure.

How can ground-level ozone affect your health?

Ozone can irritate your respiratory system, causing you to start coughing, feel an irritation in your throat and/or experience an uncomfortable sensation in your chest.

Ozone can reduce lung function and 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 uncomfortable. If you are exercising or working outdoors, you may notice that you are taking more rapid and shallow breaths than normal.

Ozone can aggravate asthma. When ozone levels are high, more people with asthma have attacks that require a doctor's attention or the use of additional medication. One reason this happens is that ozone makes people more sensitive to allergens, which are the most common triggers for asthma attacks. Also, asthmatics are more severely affected by the reduced lung function and irritation that ozone causes in the respiratory system.

Ozone can inflame and damage cells that line your lungs. Within a few days, the damaged cells are replaced and the old cells are shed-much in the way your skin peels after a sunburn.

Ozone may aggravate chronic lung diseases such as emphysema and bronchitis and reduce the immune system's ability to fight off bacterial infections in the respiratory system.

Ozone may cause permanent lung damage. Repeated short-term ozone damage to children's developing lungs may lead to reduced lung function in adulthood. In adults, ozone exposure may accelerate the natural decline in lung function that occurs as part of the normal aging process.

Healthy Lung      Inflamed Lung
Ozone can inflame the lung's lining. These photos show a healthy lung air way (left)
and an inflamed lung air way (right).

Are there always symptoms?

Ozone damage also can occur without any noticeable signs. People who live in areas where ozone levels are frequently high may find that their initial symptoms go away over time-particularly when exposure to high ozone levels continues for several days. 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.

How can you avoid unhealthy exposure to ozone?

Your chances of being affected by ozone increase the longer you are active outdoors and the more strenuous the activity you engage in. If you're involved in an activity that requires heavy exertion, you can reduce the time you spend on this activity or substitute another activity that requires more moderate exertion (e.g., go for a walk rather than a jog). In addition, you can plan outdoor activities when ozone levels are lower, usually in the morning or evening.

Examples of activities that involve moderate exertion include climbing stairs, playing tennis or baseball, simple garden or construction work, and light jogging, cycling, or hiking. Activities that involve heavy exertion include playing basketball or soccer, chopping wood, heavy manual labor, and vigorous running, cycling, or hiking. Because fitness 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.

Air Quality Index

The Air Quality Index, or AQI, is a scale used to report actual levels of ozone and other common pollutants in the air. The higher the AQI value, the greater the health concern. As shown in the table below, the AQI scale has been divided into categories that correspond to different levels of health concern.

AIR QUALITY INDEX
Index Values
Descriptors Cautionary Statements for Ozone
0 to 50
Good None.
51 to 100
Moderate Unusually sensitive people should consider limiting prolonged outdoor exertion.
101 to 150 Unhealthy for Sensitive Groups Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.
151 to 200 Unhealthy Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion.
201 to 300 Very Unhealthy Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion.

A specific color has been assigned to each AQI category. For example, red means "unhealthy" conditions and purple means "very unhealthy" conditions. This color scheme can help you quickly determine if air pollutants are reaching unhealthy levels in your area.

You may see the AQI for ozone reported in your news paper or on your local television or radio station. Here's the type of report you might hear:

The Air Quality Index today was 160. Air quality was unhealthy due to ozone. Hot, sunny weather and stagnant air caused ozone in Center City to rise to unhealthy levels.

The illustration below shows how you might see the AQI used in a newspaper. In this example, an AQI value of 130 is reported, which means that ozone levels are unhealthy for sensitive groups.

Air Quality Index Pollutant: Ozone
Today's Forecast: 130
Quality: Unhealthy for Sensitive Groups

Children and people with asthma are the groups most at risk.

About AIRNow

AIRNow logo

AIRNow (htpp://www.epa.gov/airnow) is an Internet site that gives daily information about ozone and how it may affect you. AIRNow contains:

  • Ozone maps that use contours based on the AQI to show levels in local areas. You can quickly determine if concentrations are reaching unhealthy levels.

  • Summertime ozone forecasts.

  • Ideas about what you can do to reduce ozone levels, such as driving less, making sure your car is well-tuned, and participating in local energy conservation programs.

  • Links to state and local air quality programs.

  • SMOG-Who Does It Hurt?, a booklet that provides more information about ozone health effects and how you can protect yourself.
Ozone Map
Maps that provide daily information about ozone levels are
available on the AIRNow web site.