Haze episodes at Syowa Station, coastal Antarctica: Where did they come from?

During our aerosol measurement program at Syowa Station, Antarctica, in 2004-2007, some low-visibility (haze) phenomena were observed during winter-spring under conditions with low winds and without drifting snow and fog. During "Antarctic haze" phenomena, the number concentration of aerosol particles and black carbon concentration increased by 1 to 2 orders higher relative to background conditions at Syowa Station, whereas surface O₃ concentration dropped simultaneously, especially after polar sunrise. Chemical analysis showed that major aerosol constituents in the haze phenomena were sea salt (e.g., Na⁺, Cl^-). Trajectory analysis and the Navy Aerosol Analysis and Prediction System model showed that plumes from biomass burning in South America and southern Africa were transported to Syowa Station, on the Antarctic coast, because of the eastward (occasionally westward) approach of cyclones in the Southern Ocean and subsequent poleward flow. This poleward flow from midlatitudes of the plume and injection of sea-salt particles during the transport might engender Antarctic haze phenomena at Syowa Station. Differences of O₃ concentration between the background and the haze conditions tended to be larger in spring (after polar sunrise) than in winter. Enhancement of sea-salt particles in the haze events can serve important roles in providing additional sources of reactive halogen species.