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.

Particles are often distinguished by their size. The terms PM₁, PM_2.5, and PM₁₀ are common ways particles are described, measured, and regulated, with the number in the subscript indicating the diameter of the particles in micrometers. Particles can also be described with the terms very-fine (PM₁), fine (PM_2.5), and coarse (PM₁₀) particles, with PM₁₀ often referred to as dust. Size affects how particles are regulated under the U.S. Clean Air Act and their health impacts.

Coal Dust

Coal dust is a type of particulate matter that contains coal. Coal dust is produced through physical processes that wear on the brittle coal rocks during mining, transport, and storage to generate small coal particles that are then uplifted to the atmosphere and carried by winds. As a result, coal dust particles tend to be larger in size, including PM_2.5 and PM₁₀, as well as even bigger PM that is visible with the unaided eye. Coal dust is lost from the atmosphere through deposition, leaving black dust films on outdoor and indoor surfaces. Coal dust contains toxic heavy metals that have serious health impacts at ambient concentrations below the U.S. Environmental Protection Agency's National Ambient Air Quality Standards.