Ozone Fact Sheet

Ozone Fact Sheet

Ozone (O3) is a highly reactive gas that is a form of oxygen. It results primarily from the action of sunlight on hydrocarbon vapors and nitrogen oxides emitted in fuel combustion.1  Ozone reacts chemically ("oxidizes") with internal body tissues that it comes in contact with, such as those in the lung. It also reacts with other materials such as rubber compounds, breaking them down.


  • Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. Ozone exposure may lead to:
    • premature death2
    • shortness of breath
    • chest pain when inhaling deeply
    • wheezing and coughing3
  • Long-term, repeated exposure to high levels of ozone may also lead to reductions in lung function, inflammation of the lung lining and increased respiratory discomfort.4
  • Exposure to elevated levels of ozone greatly increases the risk of asthma attacks, need for medical treatment and for hospitalization in persons with asthma.5
  • The U.S. Environmental Protection Agency (EPA) estimates one out of every three people in the United States is at a higher risk of experiencing problems from ground-level ozone.6  Five groups of people are at particular risk:
    • people with pre-existing respiratory disease; those already afflicted with lung disease such as asthma, chronic bronchitis and emphysema7
    • senior citizens8
    • people who work or exercise outdoors9
    • children, because their airways are smaller, their respiratory defenses are not fully formed, and their higher breathing rates increase their exposure10
    • "responders"—otherwise healthy individuals who experience health effects at lower levels of exposure than the average person.
  • Ozone levels typically rise between May and October when higher temperatures, an increased amount of sunlight, and stagnant atmospheric conditions promote transformation of air pollutants into ozone.
  • For almost two decades prior to 1997, the federal air quality standard for ozone had been 0.12 parts per million (ppm) averaged over one hour, but tests carried out on healthy adults and children undergoing moderate exercise while exposed to lower levels of ozone showed a decrease in subjects' breathing ability.11
  • In response to a lawsuit filed by the American Lung Association, the U.S. Environmental Protection Agency in July 1997 set a more protective ozone standard of 0.08 ppm averaged over an eight-hour period. Compliance is based on the fourth highest reading per year averaged over three years.12
  • The national ozone standard is under review currently, the result of yet another American Lung Association legal action. EPA had not formally reviewed scientific research on ozone since 1996, although the Clean Air Act requires such reviews every five years.  The American Lung Association took legal action in December 2002, to require the Agency to schedule a formal review.  In a settlement, EPA agreed to complete that review by December 2007.
  • To reduce ozone air pollution, the American Lung Association supports stringent controls on motor vehicles and commercial and industrial sources of the hydrocarbon compounds and nitrogen oxide emissions.  These controls include:
    • stricter pollution control requirements for power plants, including those that will bring older power plants up to current emissions standards
    • stronger pollution control requirements for new motor vehicles and small engines
    • cleaner fuel standards, including diesel
    • cleaner diesel vehicles, especially heavy equipment and other diesel engines
    • improved in-use performance of existing pollution control equipment
  • The ground-level ozone in the lower atmosphere (troposphere) should not be confused with the natural protective layer of ozone in the upper atmosphere (stratosphere). Although both are made of the same molecules (ozone), the ozone in the upper atmosphere protects us from the sun's harmful ultraviolet rays, while the ozone in the lower atmosphere harms us.

For more information, call the American Lung Association at 1-800-LUNG-USA (1-800-586-4872), or visit our web site at http://www.lungusa.org.



Beginning our second century, the American Lung Association is the leading organization working to prevent lung disease and promote lung health. Lung disease death rates continue to increase while other leading causes of death have declined. The American Lung Association funds vital research on the causes of and treatments for lung disease. With the generous support of the public, the American Lung Association is "Improving life, one breath at a time." For more information about the American Lung Association or to support the work it does, call 1-800-LUNG-USA (1-800-586-4872) or log on to www.lungusa.org.

1 http://www.epa.gov/air/urbanair/ozone/what.html
2 Bell, M.L., Dominici, F. and Samet, J.M. A Meta-Analysis of Time-Series Studies of Ozone and Mortality with Comparison to the National Morbidity, Mortality, and Air Pollution Study. Epidemiology, Vol. 16, pp. 436-445, July 2005; Ito, K., De Leon, S. F. and Lippmann, M. Associations Between ozone and Daily Mortality: Anaylsis and Meta-Analysis. Epidemiology, Vol. 16, pp 446-457, July 2005; Levy, J. I. Chemerynski, S. M. and Sarnat, J.A. Ozone Exposure and Mortality: An Empiric Bayes Metaregression Analysis. Empidemiology, Vol. 16 pp. 458-468. July, 2005. 
3 U.S. Environmental Protection Agency, Smog–Who Does It Hurt? What You Need to Know About Ozone and Your Health, EPA-452/K-99-001, July 1999. 
4 Künzli, N., Lurmann, F., Segal, M., Ngo, L., Balmes, J., and Tager, I.B. Association Between Lifetime Ambient Ozone Exposure and Pulmonary Function in College Freshmen–Results of a Pilot Study. Environmental Research, Vol. 72, pp. 8-23, 1997.
5 Gent, J.F., Triche, E.W., Holford, T.R., Belanger, K., Bracken, M.B., Beckett, W.S. and Leaderer , B.P. Association of Low-Level Ozone and Fine Particles with Respiratory Symptoms in Children with Asthma. Journal of the American Medical Association. Vol. 290, No. 14, pp. 1859-1867, October 8, 2003; Desqueyroux, H., Pujet, J.-C., Prosper, M., Squinazi, F., Momas, I. Short-Term Effects of Low-Level Air Pollution on Respiratory Health of Adults Suffering from Moderate to Severe Asthma. Environmental Research Section A, Vol. 89, pp. 29-37, 2002; and Burnett, R.T., Brook, J.R., Yung, W.T., Dales, R.E., and Krewski, D. Association between Ozone and Hospitalization for Respiratory Diseases in 16 Canadian Cities. Environmental Research, Vol. 72, pp. 24-31, 1997. 
7 Desqueyroux, H., Pujet, J.C., Prosper, M., Le Moullec, Y., Momas, I. Effects of Air Pollution on Adults with Chronic Obstructive Pulmonary Disease. Archives of Environmental Health, Vol. 57, No. 6, pp. 554-560, Nov. – Dec. 2002; and Höppe, P. Peters, A., Rabe, G., Praml, G., Lindner, J., Jakobi, G., Fruhmann, G., and Nowak, D.  Environmental Ozone Effects in Different Population Subgroups. International Journal of Hygiene and Environmental Health. Vol. 206, pp. 505-516, 2003. 
8 Delfino, R.J., Murphy-Moulton, A.M., and Becklake, M.R. Emergency Room Visits for Respiratory Illnesses among the Elderly in Montreal: Association with Low Level Ozone Exposure. Environmental Research, Section A, Vol. 76, pp. 67-77, 1998. 
9 Kinney, P.L. and Lippmann, M. Respiratory Effects of Seasonal Exposures to Ozone and Particles. Archives of Environmental Health, Vol. 55, No. 3, pp. 210-216, May/June 2000. 
10 Peters, J.M., Avol, E., Gauderman, W.J., Linn, W.S., Navidi, W., London, S.J., Margolis, H., Rappaport, E., Vora, H., Gong, H., and Thomas, D.C. A Study of Twelve Southern California Communities with Differing Levels and Types of Air Pollution II. Effects on Pulmonary Function. American Journal of Respiratory and Critical Care Medicine, Vol. 159, pp. 768-775, 1999; and Thurston, G.D., Lippmann, M., Scott, M.B., and Fine, J.M. Summertime Haze Air Pollution and Children with Asthma. American Journal of Respiratory and Critical Care Medicine, Vol. 155, pp. 654-660, 1997. 
11 U.S. EPA, Office of Air Quality Planning and Standards, Review of National Ambient Air Quality Standards for Ozone, Assessment of Scientific and Technical Information, OAQPS Staff Paper, EPA-452/R-96-007, June 1996. 
12 U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone; Final Rule, Federal Register, Vol. 62, No. 138, July 18, 1997.


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