Pollutants Particulate Matter (PM)

Description:
PM can be either solid particles or liquid droplets. PM is measured in micrometers, with matter less than 10 micrometers in diameter posing the greatest health risk. Particles less then 2.5 micrometers in diameter are described as being 'fine' particles. These particles are easily inhaled and can become lodged in the lungs and produce respiratory illness.

Source:
PM derives from both man-made and natural sources. Natural sources of PM include volcanic ash, salt from ocean spray, forest fires, and dust from fields. Statistics show that natural sources produce roughly 14 times as much PM as man-made sources. Volcanic eruptions in particular produce large quantities of PM.

Still, man-made particles can contribute to human health risks. Unlike remote natural disasters, man-made processes tend to be concentrated in areas where many people live. The burning of wood, diesel, and other fuels all produce PM. Various processes that take place in industrial plants, such as incineration, are also large sources of PM distribution. PM greater then 2.5 micrometers in diameter is usually the result of smoke and dust from industry and agricultural production, while particles less then 2.5 generally come from combustion of fossil fuels.