Airborne microplastics over the Baltic: the role of sea-spray emission

, Ferrero Luca, Scibetta Lorenzo, Markuszewski Piotr, Mazurkiewicz Mikolaj, Drozdowska Violetta, Makuch Przemysław, Jutrzenka-Trzebiatowska Patrycja, Zaleska-Medynska Adriana, Andò Sergio, Saliu Francesco, Nilsson Douglas E., Bolzacchini Ezio.

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.

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