Airborne Particulate Matter

The Minnesota Department of Health prepared this Web page to provide answers to questions about the health effects of particulate matter (PM), and ambient air quality. For additional information:

What is particulate matter?

Particulate matter (PM) is a complex mixture of solid and liquid particles that are suspended in air. These particles typically consist of a mixture of inorganic and organic chemicals, including carbon, sulfates, nitrates, metals, acids, and semi-volatile compounds.

The size of PM in air ranges from approximately 0.005 to 100 micrometers (µm) in diameter -- the size of just a few atoms to about the thickness of a human hair. Researchers have defined size categories for these particles differently. For the purposes of this Web page, PM is defined by three general categories commonly used by the U.S. Environmental Protection Agency (U.S. EPA): coarse (10 to 2.5 µm), fine (2.5 µm or smaller), and ultrafine (0.1 µm or smaller).

Research suggests that particle size is an important factor that influences how particles deposit in the respiratory tract and affect human health. Coarse particles are deposited almost exclusively in the nose and throat; whereas, fine and ultrafine particles generally are able to penetrate to deep areas of the lung. Fine and ultrafine particles are present in greater numbers and have greater surface area than larger particles of the same mass, and they are generally considered to be more toxic.

How might I be exposed to particulate matter?

trafficPeople are exposed to PM from both naturally occurring processes and human activities. Major sources of PM include cars, trucks, construction equipment, coal-fired power plants, wood burning, vegetation, and livestock. PM can be directly released when coal, gasoline, diesel fuels, and wood are burned or may be formed in the atmosphere from chemical reactions of nitrogen oxides, sulfur oxides, organic compounds, and ammonia.

Because of their small size, fine particles tend to remain in the air for long periods of time (weeks or months) and may be transported for hundreds (or thousands) of miles. With changing wind patterns and atmospheric conditions, fine particle concentrations can fluctuate up or down from one day to the next, or even from hour to hour.

People also are exposed to PM indoors, mostly from cigarette smoke, home heating sources (such as wood burning stoves), and cooking, but also from outdoor PM that can easily enter indoor environments. Indoor exposures to PM may be substantial because this is where people spend most of their time.

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How can particulate matter affect my health?

Over the past fifteen years an increasing number of studies have reported associations between the levels of PM in the air and adverse respiratory and cardiovascular effects in people (e.g., increases in daily mortality, illness, hospital admissions and emergency room visits). Scientists have observed these associations even at relatively low ambient levels that are prevalent in the U.S. and Western Europe. Research is currently underway to better understand the nature of the relationship between PM and disease - especially how PM affects human health.

The health effects of PM are likely to depend on several factors, including the size and composition of the particles, the level and duration of exposure, and age and sensitivity of the exposed person. Symptoms of exposure may include a sore throat, persistent cough, burning eyes, wheezing, shortness of breath, tightness of chest, and chest pain. PM may also trigger asthma or may lead to premature death, particularly in the elderly who have preexisting cardiovascular and respiratory diseases.

Because the symptoms associated with exposure to PM also may be caused by several other factors (e.g., exposure to allergens, molds, ozone, and other air pollutants), it is often difficult to determine whether PM or some other factor is responsible for an individual's symptom(s). Additional research is needed to better understand the relationship between these factors and disease, and to determine how specific characteristics of PM cause adverse health effects.

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Are some people more sensitive to the effects of particulate matter?

Some people, such as the elderly and people with respiratory and cardiovascular diseases, are more susceptible than others to the effects of PM. Susceptible groups include children and adults with asthma, bronchitis, and respiratory infections. Researchers are working to better understand the factors leading to increased susceptibility to PM health effects.

Children may be especially vulnerable to exposure to PM and other air contaminants because they breathe more air per pound of body weight relative to adults. In 2001, The U.S. Centers for Disease Control and Prevention estimates that approximately 4.2 million children had at least one asthma attack in the previous year. These children are more likely to experience asthma attacks triggered by PM and other air pollutants, such as ground-level ozone.

In addition, people of all ages who are active outdoors may be at increased risk because during physical activity greater amounts of PM may penetrate into deep parts of the lung that are vulnerable to injury. For example, children and adults who play on outdoor sports teams and participate in other outdoor physical activities may be at increased risk.

Note that on most days air quality in Minnesota is good to moderate, and there are no recommendations to limit physical activity for most people. Regular physical activity is an important part of maintaining a healthy weight and healthy body.

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What is the Air Quality Index, and how can I use it to find more information about air quality in Minnesota?

The Air Quality Index (AQI) is an indicator of air quality. It tells you how clean or dirty your air is, and what steps you can take to protect your health. The AQI ranges from 0 to 500 and is based on the measured or estimated levels of five air pollutants regulated by the federal Clean Air Act: fine PM, ground level ozone (smog), carbon monoxide, sulfur dioxide, and nitrogen dioxide.

The Minnesota Pollution Control Agency (MPCA) reports information about air quality on a daily basis on the AQI Index for Minnesota website. When the AQI exceeds or is forecast to exceed a value of 100, the MPCA issues air pollution alerts to television, radio, and print media to inform the public.

Air pollution advisories may also be issued when the AQI is below 100 and air quality is expected to worsen. As the AQI increases above 100, additional recommendations are made to reduce exposures to PM and other air pollutants. You can request email notification of air alerts by subscribing:

In recent years the MPCA has issued a handful of air pollution alerts in the Twin Cities and greater Minnesota (e.g.,Rochester). These alerts have all been based on elevated levels of fine PM or ground-level ozone. The MPCA continually evaluates data from its air monitoring network to inform the public about potential health risks. For more information about air quality monitoring in Minnesota, see:

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What can I do to reduce my risks from exposure to particulate matter?

To reduce risks from exposures to PM, follow these steps:

  • Avoid exposure to tobacco smoke, wood smoke, vehicle exhaust, and other sources of airborne particles, where possible.
  • Avoid prolonged outdoor exertion near high-traffic areas.
  • Stay informed about air pollution alerts and advisories in your area, and follow MPCA recommendations regarding outdoor physical activity on the AQI for Minnesota website, AQI Information Line (651-297-1630), and EnviroFlash Air Quality Notification system.
  • If you experience respiratory or cardiovascular symptoms (e.g., persistent cough, burning eyes, wheezing, shortness of breath, tightness of chest, or chest pain) on air quality alert days, consult with a health care professional, as needed. Pay particular attention if you are an athlete, or if you or your children have a respiratory or cardiovascular condition.
  • Work together with others in your community to reduce PM and improve air quality (for tips, see Ways to Reduce Air Pollution and Cleaning Up Commonly Found Air Pollutants).

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What are government agencies and others doing to reduce health risks from particulate matter?

The U.S. EPA establishes National Ambient Air Quality Standards for PM and other criteria air pollutants. These include daily and annual average standards for both coarse and fine PM. In September 2006 the U.S. EPA promulgated a revised daily standard for fine PM (lowered the 24-hour standard from 65 to 35 ug/m3 of air) to provide increased public health protection. However, they retained the annual standard of 15 ug/m3despite recommendations to lower this standard by their scientific advisors.

The MPCA, which is the lead state agency for monitoring and regulating air quality in Minnesota, is continually collecting and evaluating data on concentrations of fine particles in Minnesota. The MPCA also is participating in research to better understand the chemical composition and emission sources of fine PM and to better understand the emission sources of fine PM in Minnesota. In addition, the MPCA, Minnesota Department of Health, and others are working together to achieve measurable, voluntary reductions in ozone, fine PM and their precursors (e.g., volatile organic chemicals, nitrogen and sulfur oxides).

Also, the MPCA and MDH are working to provide information to the public about air quality and health through the Air Quality Index/Levels. As research becomes available, state agencies are evaluating PM studies conducted by the U.S. EPA and other national researchers. Several studies are underway to provide answers to fundamental questions regarding the relationship between PM and disease:

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Where can I find more information?

For additional information about monitoring and regulating PM:

Other Resources

U.S. Environmental Protection Agency

California Environmental Protection Agency, Air Resources Board

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Updated Tuesday, May 26, 2015 at 09:08AM