Ozone Exposure


Ozone exposure is the breathing in of ground-level, or tropospheric, ozone.


Ozone is a gas found both above and on Earth. Ozone found 10–30 miles (16–48 km) above Earth's surface is important in protecting Earth from the sun's ultraviolet rays. Ozone found at ground level is considered a health threat. Although ozone is everywhere, the concentration depends on various factors, including the amount of smog and pollution in a particular area. Warm weather also increases the level of ozone in the air. Ozone levels indoors often are between 20–80% of the level found outdoors, depending on whether windows are open or closed and if air conditioning is used.

The air quality index ranges from 0–500. Ozone is one component of this index. An air quality index between 0–50 is considered good, and air pollution poses little or no health risk. Other air quality index ranges include: moderate (51–100), unhealthy for sensitive groups (101–150), unhealthy (151–200), very unhealthy (201–300), and hazardous (301–500). At the level hazardous, everyone may experience serious health effects. Ozone concentration itself is measured in parts per million (ppm) or parts per billion (ppb).


Ground-level or tropospheric ozone, is the so-called “bad ozone” found at Earth's surface. This ozone is formed when air containing nitrogen oxide and volatile organic compounds react with sunlight. The major sources of these compounds come from the combustion of fossil fuels, such as pollutants from motor vehicles, gasoline vapors, factories, and chemical solvents. Ozone forms smog and is usually at its highest level during hot sunny days. Wind can transport ozone for long distances, meaning even rural areas may experience high levels of ozone concentration.


People who live in areas with high levels of ozone, such as large cities with heavy industry and many cars, are at the highest risk of developing symptoms of ozone exposure. Additionally, those who spend large amounts of time outdoors, especially exercising or doing manual labor, are at risk of developing symptoms due to ozone exposure, especially in areas where there is heavy smog. Children are at highest risk of ozone exposure because they often spend hours outdoors during the warm season. People with chronic respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are more vulnerable to the effects of ozone than healthy adults. Scientists also have found that some people are more sensitive to the ozone than others, but they have not found a particular reason why these otherwise healthy people are so sensitive.

Abnormal heart rhythm.
A disease in which the air passages of the lungs become inflamed and narrowed.
A respiratory disorder caused by a viral or bacterial infection. Bronchitis is characterized by inflamed bronchi, excessive mucus production, and coughing.
A lung disease in which there is an abnormal accumulation of air in the tissues. Symptoms often include trouble breathing and a cough. Emphysema is frequently caused by long-term smoking.
A type of smoky fog that contains large amounts of air pollutants.

Causes and symptoms

Symptoms associated with ozone exposure are dependent on the concentration and length of the exposure. Even short-term exposure at low concentrations can be harmful to the upper respiratory tract and the lungs. Shortness of breath, tight chest, dry throat, coughing or wheezing, headaches, nausea, and feeling unable to breathe are other symptoms of short and low-concentration ozone exposure (0.25–0.75 ppm). Even exposure at relatively low concentrations has been associated with severe lung injury and in some cases death.

As the length and concentration of exposure increases, symptoms may become more severe. Extreme fatigue, reduced lung function, the inability to sleep or concentrate, dizziness, and discoloration of the skin have been seen in people who experience intermittent exposure (9 ppm) between 3–14 days. Ozone exposure can irritate the eyes within minutes at intermittent levels.

Near unconsciousness and severe respiratory irritation were seen in one study of 15 minutes of exposure to levels at 11 ppm. Researchers believe that 30 minutes of exposure to 50 ppm can be lethal. Other research has linked ozone exposure to a particular type of cardiac arrhythmia that is associated with a risk of premature death and stroke.


For most people, no specific treatment is needed for ozone exposure. People who experience symptoms related to ozone exposure should move indoors where the concentration of ozone is lower. Symptoms will typically lessen and disappear on their own after a few hours. People with chronic respiratory problems or who continue to experience symptoms hours after moving to an area with a low ozone concentration may need to seek medical treatment for the specific symptoms they are experiencing.


Symptoms that are associated with low levels of ozone exposure usually disappear within 18 hours after the exposure has ended. Long-term effects due to higher concentrations of exposure or a longer exposure period may include headaches, irritation of the nose and throat, accelerated aging of the lungs, a decreased lung capacity and function of the lungs, and may worsen asthma, emphysema, and bronchitis. Not yet studied in humans but seen in animal populations, ozone exposure may lead to increased susceptibility to bacterial infections of the respiratory system. Studies also have associated increased mortality, especially in older adults and during the warm season, with ozone exposure. The World Health Organization (WHO) estimated that two million people worldwide died in 2012 because of continued exposure to air pollution. The same year, the U.S. Environmental Protection Agency (EPA) attributed 40,000–50,000 deaths to air pollution exposure.


People can protect themselves from dangerous levels of ozone exposure by reducing the amount of time spent outdoors when the air quality index in their area is listed as unhealthy. Ozone levels are often at their highest during warm months (April to October) and during the afternoon and evening hours. Limiting the amount of strenuous exercise during unhealthy air quality index periods will also reduce the amount of ozone exposure experienced. Ozone levels are usually lowest indoors when air-conditioning is used and air turnover rate is low.

Many governments and organizations are working to lower the amount of ground-level ozone. Regulations regarding the combustion of fossil fuels and other pollutants can help limit the amount of nitrogen oxide and volatile organic compounds released into the air. The United Nations Environment Programme, EPA, and many state and national governments all play an important role in working to reduce the formation of ground-level ozone. For example, the EPA Clean Air Act has set health-based standards for ozone in the air.


See also Air pollution ; Asthma ; Bronchitis ; Clean Air Act (1963, 1970, 1977, 1990) ; Chronic obstructive pulmonary disease ; Ozone ; Smog .



Devlin, Robert B., et al. “Controlled Exposure of Healthy Young Volunteers to Ozone Causes Cardiovascular Effects.” Circulation 126 (2012): 104–111. http://circ.ahajournals.org/content/126/1/104.full (accessed October 12, 2012).


AIRNow. “Air Quality Index (AQI)—A Guide to Air Quality and Your Health.” http://airnow.gov/index.cfm?action=aqibasics.aqi (accessed May 13, 2018).

Environmental Protection Agency. “Health Effects of Ozone in the General Population.” https://www.epa.gov/ozone-pollution-and-your-patients-health (accessed May 12, 2018).

Environmental Protection Agency. “Ozone and Your Health.” http://www.epa.gov/airnow/ozone-c.pdf (accessed May 12, 2018).


American Lung Association, 1301 Pennsylvania Ave. NW Suite 800, Washington, DC, 20004, (202) 785-3355, (800) LUNGUSA (586-4872), Fax: (202) 202 452 1805, http://www.lungusa.org .

Environmental Protection Agency, Ariel Rios Bldg., 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) 272-0167; TTY (202) 272-0165, http://www.epa.gov .

United Nations Environment Programme, United Nations Avenue, Gigiri, PO Box 30552, 00100, Nairobi, Kenya, 254(20) 76-1234, Fax: 254(20) 76-448990, unepinfo@unep.org, http://www.unep.org .

Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.