A personal cascade impactor: design, evaluation and calibration

A cascade impactor has been developed that is suitable for personal sampling. The impactor can be used with four, six, or eight stages with cut points ranging from 0.5 micron to 21 micron aerodynamic diameter. Although the impactor can be operated over a fairly wide flow rate range, it is designed specifically to be operated at 2 L/min so that a personal sampler may be used as the air mover. The nozzles of the impactor are radial slots with six slots per stage for the first six stages. Circular nozzles arranged in a radial pattern are used for the last two stages. On each stage, the area between the nozzles is used as the impaction surface for the stage before it. This design allows for the impactor to be compact, rugged and lightweight (170 gm for the four-stage design). The impactor stages are contained in a mounting bracket that can be clipped to the lapel or pocket. Although the impactor is designed for personal use, it also can be used as a compact impactor for general sampling tasks. The particle cut-off characteristics of each stage and the interstage losses were determined using monodisperse aerosols. The particle losses were found to be low and the cut-off characteristics sharp. Thus, size distributions can be obtained as accurately as with larger cascade impactors.