Evolution of size-segregated aerosol mass concentration during the Antarctic summer at Northern Foothills, Victoria Land

Within the framework of the Italian National Programm for Antarctic Research (PNRA), the first direct gravimetric measurements of size-segregated aerosol fractions were carried out at Faraglione Camp, ~3- km far from the Italian station “M. Zucchelli” (Terra Nova Bay, Ross Sea), during the 2014e2015 austral summer. A six-stage high-volume cascade impactor with size classes between 10 mm and 0.49 mm, and, in parallel, for comparison purposes, a PM10 high-volume sampler (50% cut-off aerodynamic diameter of 10 mm) were used. A 10-day sampling strategy was adopted. Aerosol mass measurements were carried out before and after exposure by using a microbalance specifically designed for the filter weight and placed inside a glove bag in order to maintain stable temperature and humidity conditions during weighing sessions. Measured atmospheric concentrations (referred to the “actual air conditions” of mean temperature of 268 K and mean pressure of 975 hPa) of size-segregated aerosol fractions showed the following values, given as size range, means (interquartile range): Dp < 0.49 mm, 0.33 (0.26e0.34) mgm3; 0.49e0.95 mm, 0.20 (0.19e0.24) mgm3; 0.95e1.5 mm, 0.16 (0.13e0.21) mgm3; 1.5e3.0 mm 0.075 (0.05e0.11) mg m3; 3.0e7.2 mm 0.12 (0.02e0.19) mg m3; 7.2e10 mm 0.06 (0.01e0.03) mg m3. The average mass concentration of the total PM10 at Faraglione Camp for the entire sampling period was 0.92 (0.67e1.1) mg m3. Although a great variability, the aerosol mass concentration showed a tri-modal distribution, with an accumulation mode (in the range 0.1e1.0 mm) and two coarse modes (CM1 in the range 1.0e3.0 mm, and CM2 in the range 3.0e10 mm). From 50% to 90% of the PM10 mass comes from particles of a size smaller than 1.0 mm. The two coarse modes represented from ~5% to ~35% of the PM10, showing opposite seasonal trends (CM1 decreased while CM2 increased). During summer, PM10 mass concentration increased to a maximum of ~1.6 mg m3 at mid-December, while in January it decreased to values that are typical of November. Both accumulation and upper super-micron fractions showed a maximum in the same period contributing to the PM10 peak of mid-summer.