Emission of primary bioaerosol particles from Baltic Sea water. bioaerosol

Bioaerosols are ubiquitous particles of biological origin which impact the biosphere, human health, the atmosphere and climate. In the atmosphere, they can play a significant role in determining the cloud phase by acting as cloud condensation or ice nuclei which is especially relevant in remote marine environments where sea spray aerosol is a major source of bioaerosols. However, the sources, emission fluxes and properties of these bioaerosols are poorly understood mostly due to difficulties with sampling and identifying these particles. Within this work, we conducted a two-week scientific cruise where a controlled sea spray experiment was used to determine the properties and flux of marine primary bioaerosols originating from Baltic Sea water. The presence of bioaerosols was probed using a novel single-particle fluorescence and light-scattering instrument, the multiparameter bioaerosol spectrometer (MBS). Using this setup we successfully differentiated primary biological aerosol particles from fluorescent particles enriched with organic matter within water spray aerosol. We determined a surface flux of primary bioaerosols emitted by bubble bursting from the seawater to be between 1.8 and 5.8 particles s−1m−2 (25th and 75th percentiles) with a mean of 4 s−1m−2, which represented 1 out of 104 particles larger than 0.8 µm in diameter of the entire sea spray particle population. During the campaign the optically-determined morphology of the nascent sea spray particles showed a clear temporal transition most likely due to changes in biochemical properties of the surface water. These temporal shifts were also observed in a clear change of the bacterial community composition of the aerosol and seawater as determined by 16S rRNA-gene analysis. The aerosol and seawater bacterial community composition were significantly distinct from each other, suggesting a preferential emission of specific bacteria to the atmosphere. Overall, our results demonstrate the capability of the MBS to detect, count and identify primary bioaerosols within sea spray and to determine their basic optical characteristics such as size, fluorescence spectra and morphology in real time and on a single-particle basis. This study will help to better constrain the emission of primary bioaerosols originating from oceanic surface water and the dependence to biochemical properties, such as the composition of microbial communities and organic matter.