No abstract

ABSTRACT. Formation of nanometer-sized particles in NH,ISOJH,OIAir mixtures by a-ray irradiation was studied experimentally to evaluate the effect of NH, 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 NH,, SO,, and H,O vapor concentrations and residence times of the gas mixture. Particle generation was enhanced in the presence of NH,, but the enhancement depends greatly on the SO,, NH,, and H,O concentrations; particle number concentrations at NH, mixing ratios of 0.71-3.6 ppm were 2-4 times higher than those in the absence of NH,, but were constant in this range of NH, concentration. The charged-particle fraction decreased with the addition of NH,, 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.

Effect of Brownian diffusion on the electrical classification of ultra fine particles in the differential mobility analyzer (DMA) has been studied theoretically and experimentally. Twokinds of particle losses which are undesirable in size analysis, (1) loss caused by the Brownian diffusion of particles traversing the sheath air stream toward the collector rod of the DMA, and (2) loss caused by Brownian diffusive deposition of particles on every wall of the DMA excluding the collector surface, were theoretically evaluated by solving the diffusion equation. Some of the calculation results were confirmed by experiments for particles of various sizes, two different lengths of DMA and various ratios of flow rate of aerosol to sheath air.

The size analysis of ultrafine aerosol particles using a loss becomes significant when particle size is smaller than ditferential mobility analyzer combined with a CNC is about 15 nm, and (2) a simple and practical data reducdiscussed from two standpoints: (1) particle loss caused tion procedure may be used, where the stationary bipolar by Brownian ditfusion in the analyzer, and (2) data charge distribution given by Boltzmann's law is modified reduction procedure where Fuchs' charging theory is by wing Fuchs' charge distribution in the smaller size applied. As a result, it has been found that (1) particle range.

No abstract