Performance evaluation of the electrical low-pressure impactor (ELPI)

The performance of the Electrical Low-Pressure Impactor (ELPI) has been eva luated using monodisperse aerosols, ELPI is a near real-time size analyzer consisting of an aerosol charger and a cascade impactor, Particle cut sizes of the cascade impactor and the charging efficiency of the charger were de termined experimentally in the designed range of the instrument, i.e. 0.03- 10 mu m. The Stokes numbers of 50% particle cut sizes of all the impactor s tages were found to vary from 0.421 to 0.483 with an average of 0.456 and s tandard deviation of 0.017. The collection efficiency curves were found to be steep with an average steepness (ratio of 70% and 30% collection efficie ncy) of 1.19. The charging efficiency of the charger was close to that spec ified by the manufacturer for particles smaller than 2 mu m in diameter. Fo r larger particles, a deviation from the-manufacturer's specifications was observed. It results from the high particle loss in the charger because of the small-size of the charger, strong trapping electric field, and the perp endicular directions of the aerosol stream and the electric field in the ch arging zone. A comparison with SMPS for size distribution measurements was made in this study. The good agreement between the two measured size distri butions shows the capability of the ELPI For near real-time particle size m easurements. (C) 1999 Elsevier Science Ltd. All rights reserved.