Particles less than 2.5 µm (micrometres) are called Particulate Matter 2.5 or PM2.5. They are 1/30th of the average width of a human hair which makes it almost negligible that cannot be seen with naked eyes. Particulate matter 2.5 can be seen only with an electron microscope. PM2.5 or fine particulate matter is 2.5 micrometers or less in diameter. These fine particles are produced from combustion, motor vehicles, power plants, residential wood burning, forest fires, industrial processes and agricultural burning.
