Time-elapsed evolution of aerosol size distributions by snow particles after the passage of blizzards over the Maitri (Antarctica)

Abstract

Measurements of the aerosol size distribution in the diameter range 0.003–20 μm were made by a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS) at Maitri (70° 45′ 52′′ S, 11° 44′ 03′′ E, Antarctica) during the 24th Indian Antarctic Expedition, which took place in January and February 2005. Time-elapsed evolutions of the aerosol size distributions on 30 January and 17 and 20 February 2005, after the passage of blizzards, were selected for estimation of the scavenging coefficient by considering the aerosol size distribution changes with snowfall over Antarctica. Scavenging efficiencies of snow particles and ice crystals collecting aerosols are obtained from the observed scavenging coefficients for 0.002–10μm aerosols. Also, theoretical snow scavenging efficiencies of snow particles and ice crystals in the diameter range 0.02–10 mm for 0.002–10 μm aerosols are determined and, thereupon, scavenging coefficients are calculated by assuming snowfall rates of 0.25 and 4 mm h−1 (in view of the reported decadal mean annual Antarctica snowfall accumulation rate of 180 mm yr−1). Snow scavenging efficiencies based on the scavenging coefficients found by considering the aerosol size distribution changes with snowfall after the occurrences of blizzards are higher than theoretical scavenging efficiencies and those of laboratory experiments for planar and columnar ice crystals. Also, the scavenging coefficients found are higher by two to three orders of magnitude than theoretical scavenging coefficients. Scavenging coefficients found from aerosol size distribution changes by snowfall after the passage of blizzards on 30 January and 17 and 20 February 2005 over Antarctica suggest that the orders of magnitude of their best estimation and the corresponding scavenging efficiencies can be viewed as being on a par with the natural snow scavenging of aerosols over this remote region.