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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. 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 death
    • shortness of breath
    • chest pain when inhaling deeply
    • wheezing and coughing
  • 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.
  • Exposure to elevated levels of ozone greatly increases the risk of asthma attacks, need for medical treatment and for hospitalization in persons with asthma.
  • 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. 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 emphysema
    • senior citizens
    • people who work or exercise outdoors
    • children, because their airways are smaller, their respiratory defenses are not fully formed, and their higher breathing rates increase their exposure
    • “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.
  • 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.
  • 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.

This article was published by the American Lung Association, copyright 2013. It can be accessed online at the following link.

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