Ozone and Air Quality
The Minnesota Department of Health prepared this Web page to provide answers to questions about the health effects from exposures to ground-level ozone. For additional information about ozone health effects, see:
For questions about current air quality conditions in Minnesota, see
What is Ozone?
Ozone is a colorless gas that occurs from natural processes and human activities. It is one component of photochemical smog.
Ozone may have very different effects depending on its location in the atmosphere. Ozone in the upper atmosphere, 10 to 30 miles above the Earth's surface, is often referred to as "good ozone." This layer of ozone provides protection from the sun’s ultraviolet rays that can damage our skin and cause skin cancer. For more information about the depletion of good ozone, see:
Ground-level ozone is formed from chemical reactions that occur when oxides of nitrogen and volatile organic hydrocarbons (VOCs) are found in the presence of heat and sunlight. This Web page focuses solely on ground-level ozone.
How might I be exposed to ozone?
People are exposed to ozone as a result of both naturally occurring processes and human activities. Pollutants emitted from power plants, cars, refineries and consumer products (e.g., paints, glues, adhesives) contribute to VOCs and nitrogen oxides that produce ozone in the presence of heat and sunlight. Due to the role of heat and sunlight in the formation of ozone, ozone is generally not a problem in Minnesota during the winter months. However, on hot sunny summer days, ozone concentrations can rise to unhealthy levels.
The reduction of ozone depends, in part, on reducing ozone precursors, namely VOCs and nitrogen oxides. While the emissions of these chemicals from vehicle exhaust systems have been decreasing, the overall emissions have been rising due to the increasing number of vehicles on the road.
When ozone is formed, winds may carry it long distances. Ozone transport can cause elevated ozone levels in rural areas. Ozone transport also can contribute to the ozone formation in the Twin Cities Metro Area, resulting in ozone concentrations considered to be unhealthy for sensitive people.
Finally, ozone may be generated indoors by air cleaners. These generators are not effective at cleaning most indoor contaminants, and the ozone released into the air may result in ozone levels that cause health problems in some people. See:
How can ozone affect my health?
Ozone affects the lungs by causing inflammation of the airways and by reducing lung function so that breathing becomes difficult. Ozone can also aggravate asthma and increase ones susceptibility to respiratory infections. Because of ozone's relative insolubility, it can persist in the airways. These properties provide an opportunity for ozone to react in the upper airways with antioxidants, proteins, and lipids.
People who have been exposed to elevated levels of ozone may experience throat irritation and notice that they cough more frequently. In addition, inhalation of ozone can cause chest pain and shortness of breath. These symptoms may become painful and can last up to several hours after exposure.
Are some people more sensitive to the effects of ozone?
Yes, a convincing body of scientific research indicates that ozone is associated with adverse health effects - particularly in susceptible populations. The health of children and adults with existing lung disease, including asthma, bronchitis, and emphysema, are of special concern on days when ozone levels are elevated. Anyone who exercises outdoors may also be at higher risk from the effects of ozone.
Children have some unique susceptibilities to ozone exposure because they are:
- More likely to spend time outside in active play during warm sunny days when ozone is most likely to form
- Less likely to heed their own bodies’ warnings
- More susceptible to the effects of ozone due to their smaller lung size and undeveloped lungs
- More likely to have asthma and more likely to be hospitalized due to asthma (for asthma statistics, see: Minnesota Asthma Data).
Ozone may aggravate or exacerbate the symptoms of asthmatics. Recent findings by the CDC National Center for Health Statistics show that in 2001, 31.3 million people (114 per 1,000) had ever been diagnosed with asthma during their lifetime. Increases in the levels of ozone have been correlated with increases in:
- Emergency room visits by asthmatics
- Hospital admissions on the day following high ozone exposures
- Asthma medication use, such as albuterol
In addition, asthmatics are more severely affected by the reduced lung function and irritation caused by ozone due to their already decreased lung capacity.
People engaged in prolonged or heavy outdoor activities may be more sensitive to the effects of ozone. Physical exertion generally causes one to breathe harder and faster. When this happens, more ozone is taken into the lungs and may reach tissues that are susceptible to injury.
With that caution in mind, however, it is important to remember that exercise and outdoor activities are critical to maintaining good health. Physical exertion helps to build a strong heart and lungs. On most days of the year, air quality in Minnesota is good to moderate, and there are no recommendations to limit physical exertion.
The Air Quality Index (AQI) for Minnesota is a tool that can help you understand whether your air quality is good or bad and how you can protect your health. It does not tell you exactly what is in the air you breathe; however, it is an indicator of air quality. The AQI does not eliminate risk but rather provides a warning system to inform at-risk individuals (groups) to take action to minimize the potential impact of harmful pollutants. The AQI ranges from 0 to 500 and in Minnesota is based on measured or estimated levels of the following four air pollutants regulated by the federal Clean Air Act: ground-level ozone, fine particulate matter (PM2.5), carbon monoxide, and sulfur dioxide.
The Minnesota Pollution Control Agency (MPCA) reports information about air quality on a daily basis on the AQI for Minnesota website and AQI Information Line (651-297-1630). When the AQI exceeds a level of health concern (100 or greater), the MPCA issues air pollution health alerts to television, radio, and print media to inform the public. Air pollution advisories also may be issued when the air quality is forecasted to be poor. People may request email notification of air alerts for ozone and other air pollutants by subscribing:
What can I do to reduce my risks from exposure to ozone?
To reduce risks from exposures to ozone, follow these steps:
- Stay informed about air quality alerts and advisories in your area, and follow MPCA recommendations on the AQI for Minnesota website, AQI Information Line, 651-297-1630, and the EnviroFlash Air Quality Notifications system.
- Avoid heavy and prolonged outdoor exertion on days when ozone levels are elevated. Ozone concentrations are generally lower in the morning and highest in the late afternoon (4-6 p.m.).
- If you experience respiratory symptoms (e.g., coughing, throat irritation, uncomfortable sensation in the chest, or difficulty breathing) on air quality alert days, consult with a health care professional, as needed. Pay particular attention to symptoms if you are responsible for active children, you are an athlete or an adult who is active outdoors, you perform moderately strenuous work outside, you or your children have an existing respiratory condition, or if you know you have an unusual susceptibility to ozone.
- If you have allergies or are particularly susceptible to ozone, modify your workout. For example, on air alert days, walk instead of run or exercise inside. Indoor concentrations of ozone are generally lower than outdoor concentrations because ozone reacts rapidly with surfaces, such as walls and fabrics. Mechanical ventilation systems also provide surfaces on which ozone can react, thereby reducing ambient ozone concentrations.
- Do not use ozone generators that are sold as indoor air cleaners,
- Do your part to reduce ozone levels in your community. Work together with others to reduce ozone and improve air quality (for tips, see What You Can Do to Clean the Air).
What are government agencies and others doing to reduce health risks from ozone?
The U.S. EPA establishes National Ambient Air Quality Standards for ozone and other criteria pollutants. In 2007 the U.S. EPA completed a review of the ozone standard and produced the following document that recommends lowering the standard to provide increased health protection for susceptible populations:
- Review of the National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Information (PDF: 9.4MB/609 pages)
Regardless of the standard and regulatory compliance, ambient ozone levels in some areas of Minnesota are at or approaching levels of potential concern for susceptible populations.
MPCA, the lead state agency for monitoring and regulating air quality in Minnesota, currently monitors for ozone to assess whether the Twin Cities Metropolitan and other areas meet U.S. EPA’s standards.
MPCA and the Minnesota Department of Health (MDH) are working to provide information to the public about air quality and health through the Air Quality Index. As research becomes available, state agencies also are evaluating ozone studies and health effects data (for more information about ozone studies, see the links below.
Where can I find more information?
For additional information about monitoring and regulating ozone:
- U.S. Environmental Protection Agency:
- Minnesota Pollution Control Agency:
- California Office of Environmental Health Hazards Assessment:
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