Nanometer-sized particle formation from NH3/SO2/H2O/air mixtures by ionizing irradiation

Formation of nanometer-sized particles in NH3/SO2/H2O/Air mixtures by a-ray irradiation was studied experimentally to evaluate the effect of NH3 gas on the gas-to-particle conversion process. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles generated in the ionization chamber were measured at various NH3, SO2, and H2O vapor concentrations and residence times of the gas mixture. Particle generation was enhanced in the presence of NH3, but the enhancement depends greatly on the SO2, NH3, and H2O concentrations; particle number concentrations at NH3 mixing ratios of 0.71–3.6 ppm were 2–4 times higher than those in the absence of NH3, but were constant in this range of NH3 concentration. The charged-particle fraction decreased with the addition of NH3, which indicated that ion-induced nucleation was decreased and homogeneous nucleation was enhanced. To evaluate the number concentrations of gaseous products, kinetic equations for the vapor species were solved on the basis of chain reactions initiated by OH radicals. From comparisons between experimental and predicted behavior, it is strongly suggested that the NH3SO3 species is the principal route to nanometer-sized particles in the NH3/SO2/H2O/Air mixture.