A new particle size magnifier (PSM) has been manufactured. In order to evaluate the performance of the PSM, the condensational growth of nltrafine aerosol particles in a supersaturated dibutyl phthalate vapor-air mixture is investigated theoretically and experimentally. First, the supersaturation ratio, the condensable DBP vapor content, and the critical size of the particle that will grow in the P S M are calculated for the mixing of hot air containing the DBP vapor with normal-temperature vapor-free air. Then the time dependence of the droplet radius during condensational growth is evaluated by numerically solving the basic equation under various conditions. From

The qtationary bipolar charging characteristics of aerosol this study wa\ found to deviate from the charge distribuparticles in the size range between 4.5 and 40 nm have tion obtained from Boltzmann's law and to agree well been studied using a new technique whereby the particles with that calculated with the bipolar charging theory of neutralized by a 2 4 1~m radioactive source are enlarged Fuchs using his values for the ion properties. The ratio of and directly observed in an electric field. The number positively charged to negatively charged particles was ratio of charged particles to total particles obtained in found to be approximately 0.35:0.65.

A new method was devised to measure the mass transfer coefficient for fine particles in high concentration. In the concentrated suspension, the mass transfer coefficient and the effect on it of agitation decreased with increasing specific surface area of the particles, although variations in the physical properties of the suspension were negligible. These tendencies could be explained by a theoretical model in which the mass transfer from part of the particle surface was impeded by solute which had diffused from adjacent particles.

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