Environmental context. Atmospheric particles play an important role in the global climate system; they contribute to the radiation balance directly, but they also have an indirect effect by modifying cloud properties and influencing precipitation. Over the Southern Ocean, nanometre-sized particle production is believed to be largely natural, although the processes that lead to these particles are not well understood. This work provides new observations of atmospheric nanoparticles, and shows that they arise from diverse sources of production.

Abstract. This paper presents analyses of a two-year record of aerosol measurements made at the Cape Grim Baseline Air Pollution Station (CGBAPS) in Tasmania covering the period 1999 and 2000. The focus of the study is nanoparticles, defined here as particles with diameter D_p, in the range 3 ≤ D_p ≤ 12 nm; with the number concentration determined using two condensation particle counters, a TSI 3025 UCPC (D_p ≥ 3 nm) and a TSI CN3760 (D_p ≥ 12 nm). Total aerosol (D_p ≥ 3 nm) and nanoparticle concentrations were examined for three broad air mass origins, namely ‘Baseline’ or background maritime, continental Australia and Tasmanian air masses. Total median aerosol concentrations in the Baseline, continental and Tasmanian sectors typically ranged from 100 to 900, 1300 to 1900 and 500 to 1200 cm^–3, respectively. The median ranges for the nanoparticle concentrations were 50–350 cm^–3 in Baseline air, 150–450 cm^–3 in continental air and 100–300 cm^–3 in Tasmanian air. While the total aerosol concentrations in the three sectors were quite different, the nanoparticle concentrations were less so. Nanoparticle diurnal concentrations showed substantial differences between the three sectors, indicative of different aerosol sources or precursor sources in the regions designated by these wind sectors.