Common Contaminants in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 262

PM 2.5

<2.5 µm in diameter

Human hair
70 µm average diameter

PM 10

<10 µm in diameter

90 µm in diameter
Fine beach sand

FIGURE 7.33
Particle size representation. (From United States Environmental Protection Agency, Particulate Matter: Basic
Information , http://www.epa.gov/particlepollution/basic.html (accessed June 28, 2010), 2010d.)

• Sulfates
• Organic chemicals
• Metals
• Soil or dust particles

The size of the particles is directly related to their potential for causing adverse health
effects. Particles less than 10 micrometers (μm) or less are small enough to pass through
the nose and throat and enter the lungs while breathing (USEPA 2009i). Once inhaled,
these particles can affect the heart and lungs and cause substantial adverse health effects.
Figure 7.33 is a diagram of particle size relative to a human hair (USEPA 2009i).
USEPA groups PM into two categories (USEPA 2009i):

• Particles ranging in size from 2.5 to 10 μm are considered inhalable coarse par-
ticles; most likely to be present near roadways and dust-producing industries.
• Particles less than 2.5 μm are considered fine particles and are present in smoke
and haze. These particles can be emitted from forest fires or power plants, certain
industries, cigarette smoke, and automobiles.

Adverse health effects caused by inhalation of PM include the following (USEPA 2009i):

• Increased respiratory irritation, coughing, and difficulty breathing
• Decreased lung function
• Aggravated asthma
• Development of chronic bronchitis