Particulate matter is the generic name used for the particles that exist in the air around us. Some particles are microscopic, others are big enough to be seen with the naked eye. Some are benign, others are highly toxic.
PM, or particulate matter, can be of various sizes. The Environmental Protection Agency uses two: PM-10 (10 micrometers or less) and PM-2.5 (2.5 micrometers or less).
The main source of particulate matter is burning fuels, meaning anything from diesel and gasoline to wood and leaves. Construction sites, roadwork, factories and quarries are other sources of particulate matter.
High concentrations of fine particulate matter can accumulate in the lungs or along the respiratory tract and become harmful for humans. The longer the exposure and the higher the amount of particulate matter, the more serious the effects, including: