- Particulate Matter ("PM")
Particulate matter (also called particle pollution) is the term to describe the mixture of microscopic airborne particles and liquid droplets suspended in air. Smoke is a is a type of particulate matter that is emitted when a material undergoes combustion or pyrolysis.
Based on size, particulate matter is often divided into two main groups:
- The coarse fraction contains the larger particles with a size ranging from 2.5 to 10 µm (PM10 - PM2.5).
- The fine fraction contains the smaller ones with a size up to 2.5 µm (PM2.5). The particles in the fine fraction which are smaller than 0.1 µm are called ultrafine particles.
Most of the total mass of airborne particulate matter is usually made up of fine particles ranging from 0.1 to 2.5 µm. Ultrafine particles often contribute only a few percent to the total mass, though they are the most numerous, representing over 90% of the number of particles.1