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Particulate Matter

This month's Wind article is dedicated to the memory of Mike Frost who passed away on January 18, 1998. Mike was a member and the Director of Environmental Programs of the Southern Ute Tribe. He was active in several air protection programs and agencies and a knowledgable instructor for the Institute for Tribal Environmental Professionals.

I know Mike will be watching our progress as we strive to continue his efforts and that somehow he will guide our actions.

Mike...we will miss you and your laughter.

Particulate Matter

1. What is "Particulate Matter" (PM)?

There are many kinds of particulate matter (PM), or particles, in the air. Some PM are natural, others are anthropogenic or man-made. They include soot from smokestacks, dust kicked up by cars on gravel and dust from bulldozing, mining and storage piles of cinders and ash.

Typical terms are, dust, fume, smoke, mist, spray, dispersion aerosol, and condensation aerosol. Based on origin and methods of formation, PM can be classified as either primary or secondary. Primary particles are produced by physical and chemical processes within a source and are emitted directly into the atmosphere, where they usually do not change form significantly. Secondary particles are formed in the atmosphere as a result of chemical reactions that involve gases.

2. Where does it come from?

The two major sources of primary particles are industrial sources and fuel combustion. In 1976, industrial processes were responsible for approximately 55-60% of all PM with fuel combustion contributing about 35%. Industrial sources include primary and secondary ferrous and nonferrous metal smelting operations, mineral rock crushing and processing, agricultural grain milling, handling and storage, coal cleaning, cement and lime production and a variety of miscellaneous manufacturing processes.

Carbon in PM may exist in the elemental form as graphite or soot or as an organic component of low volatility. Such carbon particles are quite small, with average diameters of 0.1 micrometers (um). A variety of metals are found in the fine particle mass of urban aerosols. The fine particle fraction is often enriched with trace metals such as lead, mercury, cadmium, vanaduim and chromium. The presence of these metals in fine particles are of public health significance as they are very biologically active and have a high probability of being deposited deep in human lung tissue.

3. How does size figure into the scheme?

PM diameters can typically range from a few hundredths of a micrometer to a hundred micrometers. In sources where particulate emissions are controlled by baghouses or electrostatic precipitators, particle sizes typically range from 0.1 to 1 um. The size of a particle will influence its behavior. For example, the "large" particles greater than 10 um are prone to settling out of the gas stream. These particles are relatively easy to collect and remove. Smaller particles less than 1 um in diameter, are more difficult to collect. They can slip through filter pores or diffuse away from water droplets or other collection media.

4. How is our health impacted?

Particle size has implications with regard to human health. In general, defense mechanisms are adequate to remove inhaled particles in excess of 2.5 um in diameter. Particles smaller than this are respirable and may be deposited in pulmonary tissue.

Because of flow patterns in the lung, particles tend to be deposited at or near airway bifurcations. As nerve endings are concentrated at these sites, the mechanical stimuli of deposited particles often leads to expulsion through coughing and sneezing.

The deposition of particles is not only influenced by particle size but also by mass concentration, molecular composition, pH, and solubility. Deposition also varies among nonsmokers, smokers and individuals with lung disease. Lung deposition is slightly higher in smokers and greatly increased in individuals with lung disease. Slow clearance of particles from the respiratory system of humans is generally considered to be detrimental since toxic substances are in contact with sensitive tissue for longer periods of time.

PM may contribute to the development of chronic bronchitis and may be a predisposing factor to acute bacterial and viral bronchitis especially in smokers and children. It may also aggravate bronchial asthma and the late stages of chronic bronchitis and pulmonary emphysema.

5. How can we tell if we are in a problem area?

The same fine particles linked to serious health effects are also a major cause of visibility impairment in many parts of the U.S. In many parts of the U.S. the visual range has been cut by over 70%. In the east the current range is only 14-24 miles vs. a natural range of 90 miles. In the west, the current range is 33-90 miles vs. a natural range of 140 miles.

Fine particles can remain suspended in the air and travel long distances. For example, a puff of exhaust from a forklift in Los Angeles can end up over the Grand Canyon, where one-third of the haze comes from Southern California. Emissions from a Los Angeles oil refinery can form particles that in a few days will help affect visibility in the Rocky Mountain National Park. Twenty percent of the problem on dirtiest days in that Park are attributed to LA-generated smog.

PM may be collected by a variety of techniques including gravitational settling, filtration, electrostatic and thermostatic precipitation and impaction. Of these, gravitational settling, filtration and impaction have been the most widely used for sampling ambient PM.

The hi-volume sampler is currently the most common sampling device employed in ambient air quality monitoring programs. It consists of a glass fiber filter and an additional second filter made of either polyurethane foam or a special type of resin. The sampler is mounted in a shelter that protects the filters from wind and debris and from direct impact of precipitation.

(For more information on hi-volume samplers, contact Graseby, 145 S. Miami Ave., Village of Cleves, OH 45002-1218, (800) 543-7412).

6. Are there regulations to protect us?

Prior to 1987, EPA's standards regulated all size particles ("total suspended particulates"), including those larger than 10 microns. By 1987 research had shown that the particles of greatest health concern were those equal to or less than 10 microns that can penetrate into sensitive regions of the respiratory tract.

EPA's last national air quality standard focused on small particles less than 10 microns in diameter (known as "PM-10"). Ten microns is approximately one seventh the diameter of a human hair. PM-10 standards are 150 micrograms/cubic meter for 24 hours and 50 micrograms/cubic meter for an annual average.

A lawsuit was filed by the American Lung Association charging EPA that a review of the PM standards was required. A court order required the EPA to finalize the PM standard by mid- July. On July 16, the new standards for ozone and PM were promulgated.

The new PM standard "PM 2.5" will regulate particles 2.5 microns or smaller in diameter, which the EPA deemed the most potentially damaging because they penetrate and remain deep in the lungs. The standard establishes an annual limit of 15 ug/m3, with a 24-hour limit of 65 ug/m3.

The PM-10 standards will remain in effect with the new PM-2.5 standards.

7. Where can I go for more information?

Contact the US EPA for more information at Region II, 290 Broadway, New York, NY 10007-1866, telephone (212) 637-3000 or visit the national website at


  1. EM Magazine. 1997. Air & Waste Management Association. Too Strict or Not Strict Enough? January issue. p. 16.
  2. EM Magazine. August issue. p. 21.
  3. Godish, T. 1988. Air Quality. Lewis Publishers, Inc. Chelsea, MI. p. 40-42.
  4. Godish, T. p. 136-138.
  5. Godish, T. p. 190-194.
  6. Jahnke, J.A. 1995. Source Sampling for Particulate Pollutants, APTI Course 450. p. 1-1
  7. Jahnke, J.A. p. 1-2.
  8. Jahnke, J.A. p. 1-3.
  9. Swiss, M. 1991. Air Pollution. Air & Waste Management Association, Pittsburgh, PA. p. 5.

Saint Regis Mohawk Tribe Environment Division