On the Sudden Increase in the Concentration of Aitken Particles in the Antarctic Atmosphere

Abstract

The concentration and size of Aitken particles were measured by use of an automatic Pollak counter equipped with a diffusion pipe for the two years from February 1977 to January 1979 at Syowa Station (69°00'S, 39°35'E), Antarctica. On the basis of these data, events of sudden increase in the concentration of Aitken particles are investigated. In the investigation are also taken into account the results of other aerosol observations simultaneously carried out, such as measurements of Mie particles (dia.>0.3μm), electronmicroscopic examination of particles, and furnace experiments for volatility measurement of Aitken particles.
It is found that there are two types of sudden increase in the concentration of Aitken particles. Type-1 is characterized by a preferential increase of fine particles less than 0.01*m in diameter, the highly volatile nature of increased particles, and a preferential occurrence in the summer months. Type-2, which always accompanies stormy weather, is characterized by an increase of particles in a wide size range, the non-volatile nature of increased particles and a minimum occurrence in the summer months. Both types of the events reported here correspond closely to the events which have been observed only on the Antarctic Ice Cap so far.
The event of Type-1, together with the results of electron-microscopic examination of particles, leads us to the tentative conclusion that Antarctica is covered with clouds of Aitken particles composed of photo-chemically produced sulphuric acid during the summer months. A ladder along which the acid particles descend to the ground may be provided by a cold frontal surface. The event of type-2 gives evidence that a cyclone system plays an important role in the transportation of maritime aerosols into the inland of the Antarctic continent.
The present results suggest that there are two main components of aerosols over Antarctica and their relative importance varies with the seasons. In the winter season, aerosols of maritime origin transported by cyclone systems are predominant, whereas in the summer season aerosols produced by nucleation of trace gases are predominant.