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The FHWA Particulate Matter (PM) Program

PM is one of the air quality criteria pollutants outlined in the Clean Air Act that are generated, in part, by motor vehicles. PM has gained interest since it is a significant pollutant coming from diesel vehicles which are critical to both the transit and transportation freight industries. Another distinction between PM and the other criteria pollutants is that one form of PM, (DPM), has been identified as a probable carcinogen and listed as an "air toxic" compound by EPA.

The FHWA has undertaken a PM Research Program to determine the contribution of mobile sources to PM emissions and to quantify this relationship as accurately as possible. This is important since areas designated as nonattainment must develop plans for reducing their emissions.

PM is unique in that it has two different standards. There is a "coarse" standard which regulates PM particles 10 µm in size or smaller and referred to as PM10. These particles are typically formed by "crustal" or earth-based material and enter the air through a variety of actions including "entrainment" into the atmosphere by wind blown dust. Particles from brake and tire wear, from pavement wear, and from other vehicle degenerative processes also contribute to this PM size. The greatest contribution from this size category has "natural" rather than "man-made" origins.

The other size of concern, and the most recent addition to the criteria standards, is for "fine" PM material referred to as PM2.5 (2.5µm or smaller). These particles are thought to be more a product of combustion sources. This material is believed to penetrate deeper into the lungs and remain lodged there rather than exhaled, causing negative impacts on health.

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Updated: 10/20/2015
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