We measured optical properties and ionic composition of the aerosol at Neumayer Station from 2004 through 2006 by an integrating nephelometer and chemical analysis of daily aerosol samples, respectively. From this unique data set we discuss the seasonality of aerosol optical parameters along with their chemical composition. Austral summer (November through March) was characterized by mean particle number concentrations of 472±260 cm**-3 compared to 168±160 cm**-3 during winter (April through October), mean scattering Ångström exponents of 1.7±0.6 compared to 1.3±0.6 during winter, and mean backscattering ratios at 700 nm of 0.21±0.13 compared to 0.17±0.08 during winter. In contrast, light scattering coefficients (ssp) showed a broad maximum during winter (4.8±5.3 1/µm for ssp(550)). The mean single scattering albedo was 0.99± at 550 nm. We further derived mass scattering and mass backscattering efficiencies for biogenic sulfate aerosol (BSA) at 450 nm, 550 nm, and 700 nm for relative humidities between 5% and 11%. At 550 nm the scattering efficiency for biogenic sulfate aerosol sigma bsBSA(550) was 8.9±0.7 m**2/g with a corresponding backscattering efficiency sigma bsBSA(550) of 1.0±0.08 m**2/g. From the seasonality of the aerosol composition we inferred a dominant contribution of sulfate aerosol regarding radiative forcing in the lower troposphere from December through January at Neumayer, while the impact of sea salt aerosol prevailed for the rest of the year.