Particulate Matter Sampler - Use of Inertial Separators

Use of Inertial Separators

Particles of different sizes have different health effects. Inertial separators are used to eliminate particles outside of the desired size range. If a gas stream containing particles of different sizes is forced to turn a sharp corner, the inertia of the large particles causes them to separate from the gas stream lines. The larger particles can be collected and removed from the gas stream after collisions with the walls of the vessel.

The two common types of inertial separators are cyclones, which spin the gas stream, causing collisions of the heavier particles with the outside of the cyclone wall, and impactors, where the gas particle stream is directed at a greased metal plate and turned at the last moment, causing the larger particles to stick to the greased plate.

Modern particulate samplers use a volumetric flow control system that pulls air through the particle separator at the velocity required to achieve the desired cutpoint.

For air pollution applications, the definition of "particulate" does not include uncombined water, and water from a particulate sample must be removed before it is weighed. This can be done either by heating the sample to evaporate the water or by placing the sample in a low humidity environment before weighing.