On the size distribution of submicron aerosols in the Antarctic atmosphere

Abstract

Size distributions of submicron aerosols at Syowa Station (69°00'S, 39°35'E), Antarctica were measured for about 5 months from August to December in 1978. An optical particle counter and an automatic size spectrometer which consists of diffusion pipes and Pollak counters were used. The size distributions over the radius range between 2×10^cm and 1×10^cm were determined hourly during the period except when the air was contaminated by local sources. The size distribution averaged for December has a bimodal structure with modal radii at 5×10^cm and 4×10^cm. The number of aerosol particles contained in 1(cm)^3 air was 450 including 100 particles whose radii were smaller than 10^cm. The total surface area of the particles was 1×10^(cm)^2,and the total volume 1×10^(cm)^3. Similar bimodal distributions were commonly found in each month. The spectral density of size distribution around the largest modal radii increased from August to December, whereas that around the smallest modal radii did not show any detectable change during the period. In order to explain the observed size distribution is required a continuous production of new particles at an average rate of the order of 10^(cm)^s^ at least. The present results suggest that the most significant origin of Antarctic submicron aerosols must be one involving the homogeneous and heterogeneous condensation process of vapour (probably of H_2SO_4) which is produced photochemically in the clean Antarctic atmosphere.