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

During austral summer 1998, aerosol particles were sampled at the Finnish s tation Aboa in continental Antarctica. The collected aerosol samples were a nalyzed for major inorganic ions, methane sulphonate, and dicarboxylates. M easured ions composed on average about one third of the total gravimetric m ass in fine particulate matter (particle diameter <2 mu m). Particulate sul phate, ammonium, and methane sulphonate were internally mixed and found pre dominantly in the submicron size range. The submicron mass size distributio n 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 id entifiable 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 m u m and a mode with great variability between 3 and 10 mu m. The overall co ncentration of sea salt was 1-2 orders of magnitude lower than concentratio ns measured in coastal Antarctica. Particulate nitrate was found almost ent irely in the supermicron size range, the most likely formation pathway bein g the interaction of nitric acid or some other reactive nitrogen compound w ith 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 235-9 55 cm(-3) between the samples and showed no obvious correlation with any ae rosol species. The great majority of these particles (>80-90%) were shown t o be smaller than similar to 0.1 mu m in diameter.