Number-size distribution and formation process of submicrometer sulfate-containing particles in the urban atmosphere of Nagoya

Abstract

Individual aerosol particles were collected in the summertime urban atmosphere of Nagoya, Japan, with an electrostatic aerosol sampler and a low-pressure impactor in order to obtain the number-size distribution and some properties of subμm particles by electron microscopy. Two characteristic types of number-size distribution of submicrometer particles were obtained in the daytime and they were discussed in relation to the formation process of sulfate-containing particles. In a type A distribution particles with radii more than 0.1 μm were present in a low number concentration and the concentration tended to increase strongly with decreasing radius in the Aitken size range. Type B distribution was characterized by a large number concentration of particles in 'accumulation mode'. In both cases sulfate-containing particles often strongly controlled the number-size distribution. Although hygroscopic particles comprised 70-80 % of particles of 0.03-0.35 μm radius for each type of distribution, those with water-insoluble inclusions (mixed particles) were present in high number fractions of particles (> 40%) collected from type B distributions. Type A distribution was considered to be closely related to the formation process of sulfate-containing particles by gas-to-particle conversion through homogeneous nucleation in the presence of a small proportion of pre-existing particles. Conversely, heterogeneous processes on pre-existing particles were important in forming the type B distribution. © 1985.