Particulate Matter (PM), (PM10) (PM2.5)
Any material that exists as solid or liquid in the atmosphere. Particulate matter may be in the form of fly ash, soot, dust, fog, fumes, etc. Small particulate matter, or PM10, is less than 10 microns in size (about one-eighth the diameter of a human hair) and is too small to be filtered by the nose and lungs. PM2.5 is small particulate matter that is less than 2.5 microns in size).