BIPOLAR CHARGING AND NEUTRALIZATION OF NANOMETER-SIZED AEROSOL-PARTICLES

An experimental study of charging and neutralization of 2.5-10 nln aer osol! particles by bipolar air ions has been carried out. The time req uired to attain the charge equilibrium slate, both for charging of ini tially uncharged particles and for neutralization of charged particles , has been previously determined using different-sized diffusive type chargers. To avoid sizing errors caused by space charge field and Brow nian diffusion effects, a tandem DMA (differential mobility analyzer) system has been used. The first DMA classifies a certain fraction of p articles, and the second one allows precise determination of their siz e. The experimental charging probabilities at equilibrium are in relat ively good agreement with calculations based on Fuchs' theory, except in the particle size range below 3 nm where large deviations have been observed. (C) 1997 Elsevier Science Ltd. All rights reserved.