EXPERIMENTAL EVALUATION OF ION-INDUCED NUCLEATION IN NANOMETER-AEROSOL FORMATION BY ALPHA-RAY RADIOLYSIS OF SO2 H2O/N-2 MIXTURES/

A new system for experimental investigation of ion-induced nucleation in particle formation by alpha-ray radiolysis is developed. Particles formed by ion-induced nucleation are charged bipolarly, but particles formed by processes such as binary nucleation are electrically neutral . A new irradiation chamber was developed that uses a low electric fie ld to prevent particle neutralization and preserve the charge distribu tion that results from alpha-ray radiolysis. The effects of the electr ic held on particle charging and radical generation were evaluated the oretically. From this analysis, it was determined that the optimum con ditions for causing particle formation and preserving the charge distr ibution can be achieved by using a 0.92 MBq(241)Am source and an elect ric field of 2 kV m(-1) in the ionization chamber. Under these conditi ons, the charge distributions of particles formed by alpha-ray radioly sis in SO2/H2O/N-2 mixtures were measured for various SO2 and H2O conc entrations. The charged-particle fraction decreased with increasing SO 2 concentration and was nearly independent of the H2O concentration. I t was determined from the results that SO2 mainly activated binary nuc leation through SO2-OH radical reactions that produced H2SO4 and forme d neutral particles. In contrast, H2O activated both ion-induced and b inary nucleation because both water ion clusters and OH radical were p roduced from H2O molecules.