A study of size-segregated aerosol chemistry in the Antarctic atmosphere

During austral summer 1998, aerosol particles were sampled at the Finnish station Aboa in continental Antarctica. The collected aerosol samples were analyzed for major inorganic ions, methane sulphonate, and dicarboxylates. Measured ions composed on average about one third of the total gravimetric mass in fine particulate matter (particle diameter <2 mu m). Particulate sulphate, ammonium, and methane sulphonate were internally mixed and found predominantly in the submicron size range. The submicron mass size distribution of these three ions had a dominant mode peaking at similar to 0.3 mu m of particle aerodynamic diameter, another mode peaking at 0.6 mu m, and an identifiable Aitken mode below 0.2 mu m. The mass size distribution of sodium, a tracer for sea salt particles, peaked in most samples slightly below 2 mu m; in addition, it had a submicron mode between similar to 0.5 and 1.0 mu m and a mode with great variability between 3 and 10 mu m. The overall concentration of sea salt was 1-2 orders of magnitude lower than concentrations measured in coastal Antarctica. Particulate nitrate was found almost entirely in the supermicron size range, the most likely formation pathway being the interaction of nitric acid or some other reactive nitrogen compound with sea-salt particles in the Antarctic atmosphere. The only dicarboxylate above the analytical limit of detection was oxalate, which was distributed in about equal quantities between the submicron and supermicron size ranges. The average total particle number concentration varied in the range 235-955 cm(-3) between the samples and showed no obvious correlation with any aerosol species. The great majority of these particles (>80-90%) were shown to be smaller than similar to 0.1 mu m in diameter.