Information about Particulate Matter (FINE) PM 2.5

Current conditions

Condensed from Health and Environmental Effects Of Particulate Matter; Office of Air Quality Planning and Standards, US EPA; July 1997.


Particulate matter originates from a variety of sources, including diesel trucks, power plants, wood stoves and industrial processes. The chemical and physical composition of these various particles vary widely. While individual particles cannot be seen with the naked eye, collectively they can appear as black soot, dust clouds, or grey hazes.

Those particles that are less than 2.5 micrometers in diameter are known as "fine" particles; those larger than 2.5 micrometers are known as "coarse" particles. Fine particles result from fuel combustion (from motor vehicles, power generation, industrial facilities), residential fireplaces and wood stoves. Fine particles can be formed in the atmosphere from gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds. Coarse particles are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations, and windblown dust.

EPA is also maintaining a national air quality standard focused on small particles less than 10 micrometers in diameter (known as "PM10") to protect against coarse particle effects. Ten micrometers are about one-seventh the diameter of a human hair.

Health Effects

Particulates are of health concern because they easily reach the deepest recesses of the lungs.

Scientific studies have linked particulate matter, especially fine particles (alone or in combination with other air pollutants), with a series of significant health problems, including:

Who is Most at Risk from Exposure to Fine Particles?

The Elderly:

Studies estimate that tens of thousands of elderly people die prematurely each year from exposure to ambient levels of fine particles. Studies also indicate that exposure to fine particles is associated with thousands of hospital admissions each year. Many of these hospital admissions are elderly people suffering from lung or heart disease.

Individuals with Preexisting Heart or Lung Disease:

Breathing fine particles can also adversely affect individuals with heart disease, emphysema, and chronic bronchitis by causing additional medical treatment. Inhaling fine particulate matter has been attributed to increased hospital admissions, emergency room visits and premature death among sensitive populations.


The average adult breathes 13,000 liters of air per day; children breathe 50 percent more air per pound of body weight than adults. Because children's respiratory systems are still developing, they are more susceptible to environmental threats than healthy adults. Exposure to fine particles is associated with increased frequency of childhood illnesses, which are of concern both in the short run, and for the future development of healthy lungs in the affected children. Fine particles are also associated with increased respiratory symptoms and reduced lung function in children, including symptoms such as aggravated coughing and difficulty or pain in breathing. These can result in school absences and limitations in normal childhood activities.

Asthmatics and Asthmatic Children:

More and more people are being diagnosed with asthma every year. Fourteen Americans die every day from asthma, a rate three times greater than just 20 years ago. Children make up 25 percent of the population, but comprise 40 percent of all asthma cases. Breathing fine particles, alone or in combination with other pollutants, can aggravate asthma, causing greater use of medication and resulting in more medical treatment and hospital visits.

Fine particles can also soil man-made materials, speed their deterioration, and impair visibility.

Air quality levels

The national primary and secondary ambient air quality standards for particulate matter are: 15.0 micrograms per cubic meter (µg/m3) annual arithmetic mean concentration, and 35.5* (µg/m3) 24-hour average concentration measured in the ambient air as PM2.5.
  1. The annual primary and secondary PM2.5 standards are met when the annual arithmetic mean concentration is less than or equal to 15.0 micrograms per cubic meter.
  2. The 24-hour primary and secondary PM2.5 standards are met when the 98th percentile 24-hour concentration is less than or equal to 35.5* micrograms per cubic meter.

* EPA lowered the 24-hour average concentration standard from 65 (µg/m3) to 35.5 (µg/m3), effective 12/18/2006.

[ mail questions to: DeAnna Oser, Ambient Monitoring Program | Back to AMP Homepage ]