BIPOLAR CHARGING OF ULTRAFINE PARTICLES IN THE SIZE RANGE BELOW 10 NM

Bipolar diffusion charging of aerosol particles in the size range of 2 .3-10 nm was studied experimentally. Charging probability for WOx nano particles as a function of particle size was measured using an Am-241 aerosol neutralizer for aerosol charging and a tandem DMA (Reischl typ e) with a VIE-06 Faraday cup electrometer for aerosol measurement. In spite of small deviations in the predictions from the theory of N. Fuc hs on bipolar aerosol charging at 2-4 nm range, the theory was seen to be valid. Correction of the deviations may be performed by adjusting the free parameters in the theory (ion mass and mobility). As a rule o f thumb, the charging probability of 2 nm particles was seen to be aro und 0.6% for negative and around 0.4% for positive particles. Copyrigh t (C) 1996 Elsevier Science Ltd