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In this study, we investigate the occurrence of primary biological aerosol particles (PBAP) over all sectors of the Southern Ocean (SO) based on a 90‐day data set collected during the Antarctic Circumnavigation Expedition (ACE) in austral summer 2016–2017. Super‐micrometer PBAP (1–16 µm diameter) were measured by a wide band integrated bioaerosol sensor (WIBS‐4). Low (3σ) and high (9σ) fluorescence thresholds are used to obtain statistics on fluorescent and hyper‐fluorescent PBAP, respectively. Our focus is on data obtained over the pristine ocean, that is, more than 200 km away from land. The results indicate that (hyper‐)fluorescent PBAP are correlated to atmospheric variables associated with sea spray aerosol (SSA) particles (wind speed, total super‐micrometer aerosol number concentration, chloride and sodium concentrations). This suggests that a main source of PBAP over the SO is SSA. The median percentage contribution of fluorescent and hyper‐fluorescent PBAP to super‐micrometer SSA was 1.6% and 0.13%, respectively. We demonstrate that the fraction of (hyper‐)fluorescent PBAP to total super‐micrometer particles positively correlates with concentrations of bacteria and several taxa of pythoplankton measured in seawater, indicating that marine biota concentrations modulate the PBAP source flux. We investigate the fluorescent properties of (hyper‐)fluorescent PBAP for several events that occurred near land masses. We find that the fluorescence signal characteristics of particles near land is much more variable than over the pristine ocean. We conclude that the source and concentration of fluorescent PBAP over the open ocean is similar across all sampled sectors of the SO. Key Points: Fluorescent primary bioaerosol particles (PBAP) were measured over all sectors of the Southern OceanModerate to good correlations were observed between PBAP and sea spray aerosol (SSA) proxiesPBAP fractions in SSA were positively correlated to concentrations of certain marine biota [ABSTRACT FROM AUTHOR]

The size distribution of atmospheric aerosols together with their composition, sources and sinks, is a key element in understanding aerosol effects on the Earth's climate. Aerosol particle size distribution and chemical composition were measured over the Southern Ocean and at Antarctic region during December 2009-March 2010. Aerosol samples were collected using multi-stage low volume Air Sampler, and an aerosol size spectrometer was employed to monitor PM mass concentration continuously. The mean mass concentrations for PM, PM and PM were 1.5, 1.0 and 0.6 μg/m, respectively at the Bharati station and were almost 2.5 times higher at the Maitri station. The mass size distribution of the aerosols measured by using a low volume air sampler exhibited a bimodal feature with a peak each in the size range of 0.4 to 0.7 μm and 3 to 5 μm. The difference in concentrations between the two locations for fine particles was comparatively lower than that for simultaneously measured coarse particles. Aerosol samples were analyzed for various water-soluble ionic constituents e.g. Na, K, Ca, Mg, NH , Cl, SO and NO . Sea-salt aerosols contributed to 86% of the measured mass over the Southern Ocean, 80% over Bharati and 76% at Maitri. The Southern Ocean being the most significant source of the particles during summer time, controls the aerosols at Bharati and Maitri sites. The present study will be helpful in simulating atmospheric processes responsible for aerosol characterization over coastal Antarctica and understanding its environmental implications related to radiation budget and climate over this region. [ABSTRACT FROM AUTHOR]