The non-rotating version of each impactor operates as a conventional impactor. In the rotating version, the nozzle and impaction plates rotate relative to each other to form a near-uniform particle deposit on each substrate over a 25-mm diameter impaction area.

Nozzle rotation spreads out the particle deposit under each nozzle, thereby reducing the deposited particle mass per unit collector area by a factor up to 1000. More particle mass can thus be collected without overloading the substrate.

A large number (up to 2000) of very small nozzles (down to 50 µm in nozzle diameter) are used to reduce the impaction velocity and particle bounce. The pressure drop is also lower, thus minimizing evaporative loss of semi-volatile particles during sampling.