Particulate Matter ("PM") is the sum of all solid, liquid particles suspended in the air many of which are hazardous. This complex mixture includes both organic and inorganic particles, such as dust, pollen, soot, smoke and liquid droplets.
Particulate Matter & Human Physiology
As seen in the image below, smaller size particles can travel deeper, bypassing the trachea and its protective screens and enter the primary bronchus, bronchioles and into the alveolus (PM <1). For those who don't know, the alveoli are those tiny grape-like sacs that are responsible for O2-CO2 exchange between the lungs and bloodstream. Embedded particles depending on what the particles are contain and are a byproduct from makes a concerning point in terms of scarring (fibrosis) and subsequently respiratory related illnesses and terminal cancers.