Size distribution of atmospheric aerosols at Maitri, Antarctica

Measurements of the concentration and size distribution of the atmospheric aerosol particles in the size range of 0.003–20 μm diameter have been made at Maitri (70°45′52″S, 11°44′03″E) during January–February, 2005. The measured particle size ranges extended from 0.5 to 20 μm throughout the period, from 0.016 to 0.7 μm in January and 0.01 to 0.4 μm in February. For short intervals of time, comprising a total period of 210 h, the measurements were made for particles in the size range of 0.003–0.16 μm. Total particle number concentrations of coarse and fine particles vary from 0.1 to 0.8 and from 100 to 2000 particles cm−3, respectively. The fine particle concentration undergoes a diurnal variation with values remaining low (300–400 cm−3) during low sun periods and increasing up to ∼750 cm−3 at noontime. The monthly-averaged number size distributions show maxima in accumulation mode at 0.772 ± 0.023 μm, in Aitken mode at 0.089 ± 0.005 μm in January which shifts to 0.03 ± 0.003 μm in February, and in nucleation mode at 0.018 ± 0.002 μm. The hourly-averaged curves can have one mode each in coarse, accumulation, and nucleation size ranges, and two modes in Aitken size range of particles. Total number concentration of particles in coarse mode is higher in oceanic than in continental air masses. Further, while the oceanic air masses have nucleation mode at 0.01 μm and Aitken mode at 0.024 μm, continental air masses have nucleation mode at 0.017 μm. Intermixing of the two air masses at coastal site results in multi-modal size distributions. It is inferred that while in continental air masses the nucleation mode particles are aged, in oceanic air masses these are likely to be transported from the upper troposphere under subsidence of cyclonic storms revolving around the continent of Antarctica.