Comprehensive Characterization of Original 10-Stage and 7-Stage Modified Berner Type Impactors

Two cascade impactors, a Berner Low Pressure Impactor (BLPI model 25/0.018) and a modified BLPI (with a lower pressure drop) were characterized experimentally. First, the critical dimensions of each impactor stage that affect the collection characteristics were measured. Second, the absolute pressures at each stage were determined. Finally, the collection efficiency curves were obtained for all stages in a range of particle sizes from 0.026-13.7 mu m. The collection efficiency of the modified impactor was measured using two condensation particle counters (CPC). Monodisperse calibration particles in the submicron size range were generated with a differential mobility analyzer (DMA). A vibrating orifice aerosol generator (VOAG) was used to produce supermicron test particles. In addition, the particle losses of both impactors were experimentally tested using ammonium sulfate particles under dry (15% RH) and wet (>80% RH) conditions. The losses were determined by rinsing a sampling foil and the corresponding impactor stage (nozzle plate, walls and spacer ring) with deionized water. Subsequently, the ammonium sulfate contents of the samples, along with the rinse water, were analyzed using ion chromatography.