Fluorescent Biological Aerosol Particles of the Southern Ocean Boundary Layer and Their Potential Role for Ice Nucleation in Clouds

Sea spray aerosol particles originate from bubble bursting at the sea surface, a region that is enriched by biological particles and biogenic compounds. The aerosolization of these compounds might be an important source of ice nucleating particles (INPs) in the remote Southern Ocean. The Wideband Integrated Bioaerosol Sensor Mk. 4 (WIBS4) detects bioaerosol particles based on fluorescence measurements in three excitation/emission wavebands, on a single particle basis. During the Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) project, fluorescent biological aerosol particles (FBAP) of the Southern Ocean (SO) boundary layer were monitored by WIBS4 as part of the Atmospheric Radiation Measurement (ARM) second Mobile Facility (AMF2) installed on the RSV Aurora Australis. Filter samples were collected for 24/48 h periods for the off-line determination of the temperature dependent INP concentrations active via immersion freezing in the temperature range from 0 to -27°C. Complementary thermal (95°C heating) and chemical (H₂O₂ digestion) analyses were performed on the filter samples to discriminate labile biogenic and organic vs. inorganic contributions to the INP populations.

In our presentation we will give an overview of the WIBS4 FBAP data collected during the four voyages of the Aurora Australis between Hobart, Tasmania (43°S) and the Antarctic stations Davies, Casey and Mawson and the Macquarie Island. The discrimination limit of the WIBS4 detection method for biological particles and biogenic compounds was deduced in the laboratory and is briefly reviewed. The statistical analysis of the deduced FBAP number concentrations and size distributions of the SO boundary layer is presented as a function of latitude and is compared with results of the composition measurements and the INP temperature spectra.

Acknowledgements: WIBS4 measurements and analysis were funded within the Helmholtz Research Program Atmosphere and Climate. The analyses of the filter samples are partly funded by the DOE Atmospheric System Research (ASR) program (DE-SC0018929). WIBS4 operation and filter/INP sampling during MARCUS received support from the Atmospheric Radiation Measurement (ARM) user facility.