What is ozone?

Ozone is a gas that is reactive, colorless, and has a strong odor, which, if inhaled, may cause lung damage. Ozone is formed through chemical reactions of oxygen in the air with other chemicals. Ozone is normally created in the upper atmosphere by sunlight or electrical charges (i.e. lightening) on normal oxygen. It can also form in the lower atmosphere when hydrocarbons (such as evaporating fuel, paint, and dry cleaning fluids) and nitrogen compounds mix with sunlight or electrical charges.

Ozone may be generated indoors by photocopy machines, laser printers, ion-generating air cleaners, and brush-type electrical motors such as sewing machines. Indoor ozone, however, turns back into oxygen on contact with indoor surfaces such as walls or furniture.

In the upper atmosphere, ozone has a beneficial effect by absorbing the harmful ultraviolet rays of sunlight. At the earth’s surface, ozone is harmful to crops, forests, building materials and the health of humans and animals. Warm, sunny days with little wind and no rainfall help to form ozone, and unhealthy levels can occur, especially in cities. Ozone can be blown long distances from highly populated areas. Ozone levels are usually higher in the afternoon and early evening after traffic and industry have released large amounts of ozone-forming materials into the air.

How does ozone exposure affect my health?

Ozone irritates the respiratory system and may cause health problems by damaging lung tissue, reducing lung function, and making the lungs more sensitive to other irritants. These health problems can occur at levels found in many cities during the summer months. It not only affects people with existing breathing problems, but also can affect healthy children and adults. Persons especially sensitive to ozone exposure are the elderly, infants, children, persons with existing respiratory issues such as asthma or allergies, asthmatics, chronic respiratory patients, pregnant women, smokers, and persons with lung cancer, cardiovascular disease or immune system deficiency. Symptoms include: irritation of the eyes, nose and sinuses; shortness of breath; chest pain; and wheezing or coughing. Other less common symptoms include: blurred vision, headache, nausea, vomiting, and fatigue.

The odor of ozone is noticeable at low levels; however, as the level of ozone increases, the ability to smell it may decrease. This is especially true when persons are frequently exposed to it. No odor and fewer symptoms may falsely give the impression of reduced exposure to ozone, even though further damage to health may be taking place. Children may suffer lung irritation but not notice or complain about symptoms. Even healthy individuals who exercise when ozone levels are high can experience reduced lung function leading to chest pain, coughing, wheezing and congestion.

How can I reduce my exposure to ozone?

The health effects of ozone are the same regardless of where exposure occurs -- indoors or outdoors. Ozone is always present at very low levels, but you can do certain things to reduce ozone sources indoors and limit your exposure to ozone outdoors. If you suspect you are experiencing ozone-related respiratory problems, you should contact your physician.

To reduce indoor sources of ozone:

  • Avoid air cleaners that generate ozone. These devices can be effective in reducing smoke, odors and other air contaminants, but can cause adverse health effects by producing excess ozone.
  • Ensure proper ventilation for rooms with ozone sources such as photocopiers.
  • Maintain electrostatic air filters regularly.

To limit your exposure to outdoor ozone:

  • Avoid exercising outdoors on days when ozone levels are at their highest.
  • Stay indoors as much as possible on “ozone alert” days.
  • Keep your motor vehicle properly tuned and drive no more than necessary on hot days.

What does the government do to protect the public from ozone?

The outdoor air is monitored for ozone. If ozone levels exceed government standards, special health statements are issued in affected areas. If similar conditions are forecast to return the next day, an ozone advisory is issued. Some government agencies also have set limits on:

  • ozone levels that can be emitted by electronic devices;
  • indoor air ozone levels to which the public may be exposed; and
  • motor vehicle emissions.

Is there a safe level of ozone in air?

The national and Illinois ambient air quality standard for ozone is 0.08 parts per million (ppm). The federal Occupational Safety and Health Administration standard is 0.1 ppm of ozone in the workplace. IDPH recommends that 0.1 ppm not be exceeded in the home. Several companies make electronic instruments that measure ozone in air.

Where can I get more information?

Illinois Department of Public Health
Division of Environmental Health
525 W. Jefferson St.
Springfield, IL 62761
TTY (hearing impaired use only) 800-547-0466

This fact sheet was supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund through a cooperative agreement with the Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services.

Updated February 2009

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Environmental Health Home

Illinois Department of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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