Measurements of aerosol particles and light scattering coefficient were carried out at Nagoya in

No abstract

Collections of aerosol particles were carried out with an electrostatic aerosol sampler in the summertime at Nagoya and Yokkaichi which are heavily polluted areas in Japan. By electron microscopic examination 21 number size distributions of all particles and those of sulfate particles, including those in the Aitken size range, were obtained. Method for the detection of sulfate ions by electron microscopy, proposed by Bigg et al. (1974), was applied to the individual particles. Sulfate particles were found to be predominant in the range of 0.016 to 0.28*m radius and they were detected with high number fractions of particles, 55 to 75* on the average. It is considered that the distributions of aerosol particles in the Aitken size range were closely related to the behavior of sulfate particles formed by gas-to-particle conversion influenced by the amount of pre-existing particles.

The role of particle-growing processes such as coagulation and condensation in the decay phase of the stratospheric aerosol layer enhanced by the volcanic eruption was discussed by using a one-dimensional and time-dependent numerical model which includes eddy diffusion, coagulation, condensation and sedimentation.Result of calculation suggests that the characteristic time of the decay of the stratospheric aerosol layer is about 1.5-3.0 years for the volcanic eruption which injects a large amount of SO2 gas into the stratosphere.

The possibility of formation of ammonium sulfate particles in the stratosphere is examined by comparing the absorption rate of ammonia gas into a sulfuric acid droplet with the condensation rate of sulfuric acid vapor onto the droplet. When the concentration of ammonia gas is sub-ppb level, the conversion time from a sulfuric acid droplet of 0.1*m radius into an ammonium sulfate particle is one to two orders of magnitude shorter than the characteristic time scales of eddy diffusion and sedimentation of particles of 0.1*m radius in the stratosphere. The contribution of coagulation to the growth of particles is smaller than that of the condensation and negligible. When the concentration of ammonia gas is low enough for the influence of the absorption to be neglected, the conversion time from an ammonium sulfate particle of 0.1*m radius into an entire liquid droplet is comparable to or longer than the characteristic time scale of eddy diffusion and sedimentation in the stratosphere.