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Strategic Workplan for Particulate Matter Research: 2000 to 2004

Appendix A

PM -- A Primer

Particle Size. PM is characterized by size, expressed as a particle's aerodynamic equivalent diameter in micrometers (or microns). Fine particles are typically defined as those less than 2.5 microns in diameter (PM2.5) and coarse mode particles are those greater than 2.5 microns, but less than 10 microns in diameter (PM10). Particle size is closely linked to relative health impacts, as well as source origination, and chemical composition.

Health Effects of PM. The adverse effects of PM on human health have been recognized for many decades. The major risks to human health include not only premature mortality from acute pollution episodes, but also aggravation of existing respiratory and cardiovascular disease, damage to lung tissue, impaired breathing and respiratory symptoms, and alterations to the body's physical and immune system defenses against inhaled particles. Populations at general risk include children, people of all ages with asthma, and elderly persons with illnesses such as bronchitis, emphysema, and pneumonia. PM causes adverse health effects by depositing in the lungs where it interferes with the respiratory process. The health risk from an inhaled dose of PM appears to depend on the size, composition, and concentration of the particulate.

PM in the Atmosphere. PM can result from direct emissions from various sources (primary PM) or it can be formed in the atmosphere by a combination of gaseous emissions (secondary PM).

Chemical Characteristics of PM. PM10 and PM2.5 are composed of varying proportions of six broad chemical constituents:

PM Regulatory Background. Regulation of PM in the United States has occurred in three broad phases, beginning in 1971:

The planned time frame for review and implementation of the PM2.5 NAAQS is shown in Figure A-1.

Figure A-1. Time Frame for Implementation of PM2.5 Standard

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Updated: 7/6/2011
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