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Airborne microplastics over the Baltic: the role of sea-spray emission
Summary
Researchers measured both airborne and marine microplastic concentrations during a research cruise across the Baltic Sea, finding higher airborne plastic concentrations near the Gdansk harbor than in the open sea. The study investigated whether sea spray from wave action could be transferring microplastics from ocean surface water into the atmosphere, potentially explaining some of the airborne plastic detected over the sea.
The concentrations of both atmospheric and marine MPs were measured over the Baltic along a research cruise that started in the Gdansk harbour, till the Gotland Island, and during the way back. A "Deposition box" was used to collect airborne MPs. Marine MPs concentrations were investigated during the cruise using a dedicated HydroBios microplastic 300 µm mesh net. MPs images were recorded both using optical camera Leica ICC50W installed on a dedicated Leica DM750P microscope allowing the quantification of microparticle length and width. Results showed airborne microplastics average concentrations higher in the Gdansk harbour (161±75 m-3) compared to the open Baltic Sea and to the Gotland Island (24±9 and 45±20 m-3). These latter values are closer to the ones measured in the sea (79±18 m-3). The MPs composition was investigated using µ-Raman (for the airborne ones) and FTIR (for marine ones after dissolution of organic matter via H2O2); similar results (e.g. polyethylene, polyethylene terephthalates, polyurethane, polystyrene) were found in the two environmental compartments. Airborne and marine MPs were characterised by similar colours: blue/black, transparent and red fibres. Moreover, airborne and marine MPs appeared correlated (R2=0.89) when considering the simultaneous available measurements and they were characterised by the same average width (17±2 and 18±5 µm, respectively) but different length (427±59 and 2060±1970 µm) suggesting that in case of sea emission of MPs only the shorter ones can remain suspended in the atmosphere. The atmospheric MPs' equivalent aerodynamic diameter was calculated (28±3 µm) showing the capability of atmospheric MPs to remain suspended in the air once emitted from the sea. The estimated MPs sea emission fluxes of MPs volume (4-18*106 µm3 m-2 s-1 range) showed the contemporary presence of atmospheric transport together with a continuous emission from the sea. Also see: https://micro2022.sciencesconf.org/427347/document