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For the first time, falling ice crystals were collected on glass slides covered with a thin layer of 2% formvar in chloroform at the Dome Concordia site (Dome C), Antarctica. Samplings were performed in the framework of the 27th Italian Antarctica expedition of the Italian National Program for Research in Antarctica in the period 21 February–6 August 2012. Events of clear-sky precipitations and precipitations from clouds were considered and the replicas obtained were examined under Scanning Electron Microscope (SEM). Several shapes of ice crystals were identified, including “diamond dust” (plates, pyramids, hollow and solid columns), and crystal aggregates varying in complexity. Single events often contained both small (10 μm to 50 μm) and large (hundreds of microns) crystals, suggesting that crystals can form simultaneously near the ground (height of a few hundred metres) and at higher layers (height of thousands of metres). Images of sampled crystal replicas showed that single bullets are not produced separately, but by the disintegration of combinations of bullets. Rimed ice crystals were absent in the Dome C samples, i.e. the only mode of crystal growth was water vapour diffusion. On considering the aerosol in the sampled crystals, we reached the conclusion that inertial impaction, interception and Brownian motion were insufficient to explain the scavenged aerosol. We therefore presume that phoretic forces play a role in scavenging during the crystal growth process. [ABSTRACT FROM AUTHOR]

The paper provides a review of past and a few new measurements of Ice-forming Nuclei (IN) in Antarctica. The few available published data were mostly obtained adopting different devices and methods and for a limited period of time. Consequently, data are scattered and give an incomplete picture of the Antarctic situation. It should be pointed out, however, that ice nucleation is an intricate process, depending on many parameters (supersaturation relative to ice and water, aerosol physical–chemical properties, possible conditioning and preactivation of particles, different modes of nucleation). Therefore, the uncertainty does not concern the Antarctic continent alone, but all measurements performed world-wide. A comparison of the published data can be made between Saxena and Weintraub (1988) at Palmer Station, and Ardon-Dryer et al. (2011) at the South Pole, as both studies measured IN in the immersion mode, even if at different temperature. Saxena and Weintraub (1988) obtained in three filters IN concentrations of about 104 m−3 at T=−6°C, −11°C and −13°C, and 103 m−3 at T=−17°C, in an additional filter (February–December 1983). At the South Pole Ardon-Dryer et al. (2011) obtained a concentration of about 5×102 m−3 at T=−19°C, and the IN concentration increased until about 40×103 m−3 at the activation temperature of −26°C. Such values are higher than those measured by Bigg (1973) near Antarctica, using a thermal diffusion chamber (deposition or deposition–condensation modes). IN concentrations measured at Terra Nova Bay are lower than those reported above, and are comparable to values reported for the Scott Base, Byrd Station and cruises at latitude 60°–70° S. [ABSTRACT FROM AUTHOR]

Abstract: During austral summer 2006, in the framework of the XXII Italian Antarctic expedition of PNRA (Italian National Program for Research in Antarctica), aerosol particle number size distribution measurements were performed in the 10–500 range nm over the Nansen Ice Sheet glacier (NIS, 74°30′ S, 163°27′ E; 85m a.s.l), a permanently iced branch of the Ross Sea. Observed total particle number concentrations varied between 169 and 1385cm−3. A monomodal number size distribution, peaking at about 70nm with no variation during the day, was observed for continental air mass, high wind speed and low relative humidity. Trimodal number size distributions were also observed, in agreement with measurements performed at Aboa station, which is located on the opposite side of the Antarctic continent to the NIS. In this case new particle formation, with subsequent particle growth up to about 30nm, was observed even if not associated with maritime air masses. [Copyright &y& Elsevier]

Abstract: The work presents the results of an experimental campaign performed at the Drop Tower Facility (Bremen) in microgravity conditions, concerning the scavenging process of an evaporating single droplet in stationary conditions. In the experimental conditions the thermo- and diffusiophoretic forces are the only ones that can determine the scavenging of the aerosol. The research is finalized to help solve the open question concerning the contribution of thermo- and diffusiophoretic forces in aerosol scavenging process due to cloud droplets. Although earlier theoretical and experimental papers have addressed this problem, the results are contradictory and inconclusive. As phoretic forces depend on aerosol diameter and water vapour pressure gradient, experiments were performed by changing the aerosol diameter (range 0.4μm–2μm) and the water vapour gradient. The experimental results show a prevalence of the diffusiophoretic over thermophoretic force, for the considered aerosol. The measured values of the particle velocities due to phoretic forces increase with increasing aerosol diameter and vapour pressure gradient. [Copyright &y& Elsevier]

Polylactide/polyhydroxybutyrate ( PLA / PHB ) nanofibers were prepared by electrospinning and functionalized with different amounts of ammonium-based ionic liquid ( IL ) belonging to quaternary ammonium compounds ( QACs ) to obtain a fibrous mat with antimicrobial properties for aerosol particle filtration. The filtration performance of these biopolymer nanofiber mats was evaluated by measuring the filter penetration of sodium chloride (NaCl) aerosol particles ranging from 20 to 600 nm. These filtration test results showed that the quality factors remain unvaried with the addition of IL and depend mostly on the electrospinning time. The “multi-layering” method was adopted to fabricate highly efficient nanofiber filters with a greatly reduced pressure drop. A quantitative analysis of the antimicrobial activity is also presented. The results show that renewable materials, such as PLA blended with PHB , can be considered for biodegradable filters, in line with the future trend to develop eco-sustainable products. Adding QAC salt to the biopolymer blend combines these qualities with an innovative bactericidal nanomaterial. [ABSTRACT FROM AUTHOR]