Particulate Matter (PM) refers to a mixture of tiny particles and droplets in the air, which can be solid or liquid. These particles come from a variety of sources, including construction sites, unpaved roads, fields, smokestacks, and fires. PM is usually categorized by size, with PM10 (particles with diameters of 10 micrometers and smaller) and PM2.5 (particles with diameters of 2.5 micrometers and smaller) being the most commonly studied due to their ability to penetrate deep into the respiratory system and enter the bloodstream.
