Examination of after-charging effects downstream of an aerosol neutralizer

Depending on the concentration of aerosol particles and the Nt product (ion number concentration x residence time), a relatively high concentration of free unattached ions may still survive long after an aerosol has left the neutralizer. The possible existence of after-charging effects downwind of a n aerosol neutralizer caused by these residual free ions has been examined. Experiments have been carried out using a commercially available neutraliz er (TSI model 3077), two different levels of aerosol concentration, varying lengths of a tube connected to the neutralizer outlet, and different mean aerosol residence times in the neutralizer. The reference charged aerosol l eaving the ionizer was mixed with a foreign uncharged aerosol. Although the foreign particles acquire electric charges by attachment of the residual f ree ions, the charge distribution of the reference aerosol remains unmodifi ed provided its mean residence time in the neutralizer is long enough for i t to attain a steady-state charge distribution. (C) 2001 Elsevier Science L td. All rights reserved.