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

- First direct gravimetric measurements of PM10 fractions in Antarctica.
- Tri-modal distribution of size-segregated aerosol mass fractions.
- Seasonal variations of sub-10 μm fractions and total measured PM10.

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 2014-2015 austral summer. A six-stage high-volume cascade impactor with size classes between 10 μm and 0.49 μm, and, in parallel, for comparison purposes, a PM10 high-volume sampler (50% cut-off aerodynamic diameter of 10 μm) 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 μm, 0.33 (0.26-0.34) μg m−3; 0.49-0.95 μm, 0.20 (0.19-0.24) μg m−3; 0.95-1.5 μm, 0.16 (0.13-0.21) μg m−3; 1.5-3.0 μm 0.075 (0.05-0.11) μg m−3; 3.0-7.2 μm 0.12 (0.02-0.19) μg m−3; 7.2-10 μm 0.06 (0.01-0.03) μg m−3. The average mass concentration of the total PM10 at Faraglione Camp for the entire sampling period was 0.92 (0.67-1.1) μg m−3. Although a great variability, the aerosol mass concentration showed a tri-modal distribution, with an accumulation mode (in the range 0.1-1.0 μm) and two coarse modes (CM1 in the range 1.0-3.0 μm, and CM2 in the range 3.0-10 μm). From 50% to 90% of the PM10 mass comes from particles of a size smaller than 1.0 μm. 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 μg m−3 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.