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Design and calibration of a low flow parallel stage impactor.

A low flow, compact Parallel Stage Impactor was designed, constructed and calibrated. This instrument has six stages: one for total collection of air particulates, and the other five with cut-off sizes of 0.34 micrograms, 0.75 micrograms, 1.90 micrograms, 3.12 micrograms and 7.43 micrograms aerodynamic equivalent diameter. Flow through the individual stages is controlled by adjustable needle valves, which act as critical orifices. Flow was 700 mL/min per stage, resulting in a total flow of 4.2 L/min. The instrument was calibrated using uranine test aerosols, photofluorescence and optical microscopy techniques. There was excellent agreement between theoretical calculations and observed performance. The instrument design details and performance suggest a rugged and reliable field instrument for particle size analysis.