An Andersen sampler or Andersen impactor is a cascade impactor used to determine the amount of viable pathogens in a given area, in particular bacteria and fungi. Unlike real-time electronic particle counters, the Andersen sampler imparts pathogens on petri dishes, which require incubation. Thus, calculation of the contaminated air requires working backwards from the resulting pathogen growth in each dish.
Andersen samplers have been used to assess the nature of pathogenic aerosols in various scientific papers. It can also be used to study inert aerosols, when each stage of the sampler is used to model respiratory particle deposition.