Preliminary Results on Aerosol Composition at Terra Nova Bay and Dome C (Antarctica) and Evidences of Superficial Snow Post-depositional Effects

More than 200 aerosol samples were collected on two dimensional classes (micrometric and sub-micrometric fraction) during the last 3 Italian Antarctic Campaigns on coastal (Terra Nova Bay - Ross Sea) and inland (Dome C) Antarctic areas. The sampling was performed by low-volume aspiration pumps using a sandwich of polycarbonate membrane filters having different porosity. Filters were analysed by Ion Chromatography for inorganic anions, cations and methanesulphonic acid (MSA). Contemporaneously with aerosol sampling, recent snowfalls, superficial snow and snowpit samples were collected. At Dome C, three different snowpits (2.5-7 m deep) were sampled together with very superficial snow crystals in order to correlate aerosol and superficial snow composition and to point out post-depositional processes. The composition of fine and coarse fractions was found to be different in the two stations, the most coastal being characterised by primary aerosol components (mainly sea spray) and Dome C by secondary aerosol inputs, such as non-sea salt sulphate and MSA from biogenic activity. The ionic balance shows a very important contribution of free acidity (H+ and carbonate were not directly determined) especially in the fine fractions both in coastal and plateau site. Very high aerosol acidity, mainly at Dome C, prevents the reliable determination of volatile acidic species, such as nitric and hydrochloric acid. These compounds and, to less extent, MSA, show post-depositional effects in the uppermost superficial layers at Dome C, where the low accumulation rate (around 3.0 cm/yr) leads to the re-emission of their acidic forms into the atmosphere. In particular, nitrate is present at very high concentration (ppm) in the superficial snow crystals but its concentration dramatically decreases to very low constant values (few ppb) in the first half-meter of snow deposition. The comparison between aerosol and snow composition and the study of post-depositional processes is necessary for the understanding of the atmosphere-snow interchange processes, helping in the interpretation of paleo-data coming from EPICA-Dome C ice core.