Explain the Air Samplers - Air Sampling?

Air Samplers, e.g., all glass impinger and the Andersen sieve samplers may be used. Volume of the air sampled is known. In all glass impinger, air is pulled through a capillary orifice by vacuum and impinges on the diluent placed in the impinger. Microorganisms are trapped in the liquid and plated for SPC. The method does not work well when numbers of organisms are too small.

In the Andersen sampler, air is drawn through one or more sieves by vacuum and the microorganisms are trapped on the surface of agar plate.  After incubation of plates, enumeration of microbial load is done.