AVL Particulate Size Classifier

An impactor is used to collect selectively particles of different sizes. An impactor is a simple device having two co-linear plates of which the upper one has small nozzles in it. Aerosol passes through these nozzles with high speed and makes a sharp turn to flow between the plates. Particles larger than a certain size cannot follow the sharp turn and impact to a second plate.

This "cutoff" size depends on the characteristic dimensions of the impactor stage. The "cutoff" diameter for an impactor stage is defined as the size of particles collected with 50% efficiency. The plate with nozzles in it is called the jet plate and the second one the collection plate. Cascade impactors consist of several successive impactor stage with decreasing cutoff diameters. The highest stage (stage 4) in the AVL PSC Particulate Size Classifier impactor has a cutoff diameter of 2.5 µ and the lowest stage (stage 1) 200 nm at a flow rate of 70 L/min.