Concentrations and size distributions of aerosol particles at Maitri during the passage of cyclonic storms revolving around the continent of Antarctica

The number size distributions of aerosol particles in the size‐range of 0.003–20 μ m diameter have been measured at Maitri (70° 45′ 52″S, 11° 44′ 03″E, 117m above mean sea level), Antarctica, when two circumpolar cyclonic storms passed close to the station during February, 2005. As a storm approaches toward Maitri, concentration of coarse particles increases by about an order of magnitude and the number size‐distribution frequently shows a coarse mode at ∼ 2 μ m, a broad Aitken mode from 0.04 to 0.1 μ m and, occasionally, a nucleation mode at 0.018 μ m diameter. When the storm is going away from Maitri, in addition to the coarse mode at ∼ 2 μ m and a peak at 0.08 μ m diameter, a nucleation mode frequently appears at < 0.01 μ m diameter and the mode existing at 0.018 μ m diameter shifts to 0.02−0.04 μ m diameter. Particles in the range of 0.008–0.03 μ m diameter grow at the rate of 0.2−0.6 nm h −1 in the case of Storm I, but no appreciable growth is observed in the case of Storm II. The peak at 0.02–0.04 μ m is often so dominant that it envelops the peak at 0.08 μ m diameter. Results are interpreted in terms of the mixing of continental and oceanic air masses with the subsidence associated with the storm. The nucleation mode at 0.01 μ m diameter has been associated with the new particles formed in the outflow at the top of clouds and the coarse mode at 2 μ m diameters with the re‐suspension of particles from the surface.