Experimental measurement of competitive ion-induced and binary homogeneous nucleation in SO2/H2O/N-2 mixtures

Alpha-ray radiolysis of SO2/H2O/N-2 gas mixtures is carried out to investigate the competitive processes of ion-induced and binary homogeneous nucleation in this system. Charged particles in the system are indicative of ion-induced nucleation and most likely involve water clusters. Charged particle neutralization was prevented by application of a dc electric field, therefore, uncharged particles in the system result from homogeneous nucleation. Hydroxyl (. OH) radicals are generated by the alpha-ray radiolysis. Oxidation of SO2 by . OH radicals leads to sulfuric acid (H2SO4) vapor molecules and to subsequent binary homogeneous nucleation of H2SO4/H2O. At increased SO2 concentrations the contribution of binary homogeneous nucleation increases relative to that of ion-induced nucleation. Electrical mobility distributions of bipolar ions and nanometer-sized charged particles were measured with a cluster-differential mobility analyzer combined with a Faraday cup electrometer. In this system, ion-induced nucleation occurred preferentially on negative rather than positive ions. (C) 1997 American Association for Aerosol Research.