**Particulate Matter (PM) is airborne dust and [particle pollution](/wiki/pm) that 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](/wiki/nonmetallicmining), 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](pm-tools), [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](https://i.publiclab.org/system/images/photos/000/003/698/original/Screen_Shot_2014-04-16_at_11.49.08_PM.png)), citation: [EPA/600/R-95/115](http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=4608)).  

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

Course 

Fines

Ultrafines

Nanoparticles

read more in [Data Collection & Monitoring](/wiki/pm-monitoring)


##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.

Read more on identifying particle concentration [Data Collection & Monitoring](/wiki/pm-monitoring).

##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](http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=4608)].

Read More in [PM Monitoring Regulations](/wiki/pm-monitoring)