Experimental studies of ion-induced nucleation

A new system for experimental investigation of ion-induced nucleation, based on a continuous flow-mixing type device, is introduced. Measurements of the ion-induced nucleation of dibutylphthalate (DBP) vapor in the presence of unipolar ions are presented. When an ionized water vapor/N₂ mixture comes into contact with DBP vapor, nucleation of DBP particles is significantly enhanced relative to that in the absence of ions for both positive and negative ions. The number concentration of DBP particles activated by ions increases with increasing ion number concentration and DBP supersaturation ratio. A definite ion polarity effect is observed; at equal saturation ratios, positive ions induce larger number concentrations than negative ions. In the absence of water vapor, an ionized N₂ stream produces nucleation rates higher than those for pure homogeneous nucleation but well below those in the presence of water vapor. The present data set should be valuable in future assessments of ion-induced nucleation theories.