View source for Particulate Matter and Coal Dust

=== '''Airborne Particles''' ===
Airborne particles––also known as particulate matter (PM), particulates, or aerosols––refer to any mixture of solids and liquid droplets in the atmosphere. Particles can be directly emitted into the air or formed through chemical reactions of gaseous pollutants. 

==== '''Particle size''' ====
Particles are often distinguished by their size. The terms PM<sub>1</sub>, PM<sub>2.5</sub>, and PM<sub>10</sub> are common ways particles are described, measured, and regulated, with the number in the subscript indicating the diameter particles in micrometers. Particles can also be described as very-fine (PM<sub>1</sub>), fine (PM<sub>2.5</sub>), and coarse (PM<sub>10</sub>) particles, with PM<sub>10</sub> often called dust.

=== '''Regulation under the Clean Air Act''' ===
Because they are harmful to our health, there are limits placed on airborne particles under the Clean Air Act. The U.S. Environmental Protection Agency (EPA) regulates PM<sub>2.5</sub> and PM<sub>10</sub> as two of six criteria pollutants that must meet specific concentration-based thresholds known as National Ambient Air Quality Standards (NAAQS), which you may hear pronounced as “the nacks”. The PM<sub>10</sub> NAAQS is a 24-hour average mass concentration of 150 μg/m<sup>3</sup>, not to be exceeded more than three times over three years. There are two PM<sub>2.5</sub> NAAQS: a 24-hour average mass concentration of 35 μg/m<sup>3</sup> and a recently revised annual average mass concentration of 9 μg/m<sup>3</sup>. The NAAQS are set to protect public health, including the health of more sensitive individuals such those with asthma as well as children and elders. That said, there is no known safe level of exposure to particles, with documented health impacts below the NAAQS. To determine NAAQS compliance, PM<sub>2.5</sub> and PM<sub>10</sub> must be measured using designated regulatory air monitors by an agency with the authority to do so, which in Virginia is the Virginia Department of Environmental Quality (VA DEQ).

=== '''Documents''' ===