**Particulate Matter (PM) is airborne dust and particle pollution that is small enough to be suspended in the air and threatens human health. Based on size alone, small particles can become lodged in the lungs or even enter the bloodstream. Some non-toxic materials, such as silica, can be carcenogenic at small size. There are four parts to determining what particles are in the air and how dangerous they are: particle size, particle concentration, particle type, and particle source, discussed below.

Identifying dust sources can be difficult, but through monitoring, [advocacy,] and behavior change we can make the world a much less dusty place. Natural sources of dust have been overtaken by human-generated particles from roads, agriculture, construction, and mining which now overshadow wind erosion, volcanoes, pollen, and forest fires as sources of particle pollution chart), citation: EPA/600/R-95/115). According to the CDC, a 10% reduction in fine particles could prevent 13,000 deaths annually in the US.

Particle Size

Image credit: CDC

Particles are measured in microns (short for micrometers, or millionths of a meter, μm), but when talking about particle sizes we use shorthand for size ranges:

Coarse

Fines

Ultrafines

Nanoparticles

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Particle Concentration

Particle concentration is the density of particles in the air. This is usually expressed as mass per volume, i.e. micrograms or milligrams per cubic meter, expressed μg/m3 or mg/m3.

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Particle Type

This can be conducted with a microscope for crystals, and using lab techniques for other types of particles. Mass spectrometry and x-ray spectrometry may also be used.

Particle Source

Usually directional and time-stamped data from multiple points are needed to extrapolate source, along with an understanding of particle type.

Researchers speak of two types of emissions that have a blurry line between them, 'process stream' emissions and 'fugitive emissions.' Process stream emissions are inherent to a process, like ash from a fire, and fugitive emissions are ancillary, like the dust kicked up bringing wood to a fire [EPA 3-2].

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