Particulate matter

Extremely small particles and droplets suspended in air. They may include organic chemicals, acids, metals, and dust or soil particles. Also known as particle pollution, particulate matter is used as a measure of air pollution. The EPA groups inhalable pollutants which pass through the throat and nose and enter the lungs into two categories: “inhalable coarse particles” (between 2.5 micrometers and 10 micrometers in diameter); and “fine particles” (2.5 micrometers in diameter and smaller).