Airborne and marine microplastics from an oceanographic survey at the Baltic Sea: An emerging role of air-sea interaction?

Microplastics (MPs) pollution is one of the most important problems of the Earth. They have been found in all the natural environments, including oceans and the atmosphere. In this study, 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 the way back. A deposition box (based on a combination of active/passive sampling) was used to collect airborne MPs while, marine MPs concentrations were investigated during the cruise using a dedicated net. Ancillary data were obtained using a combination of particle counters (OPC, LAS and CPC), Aethalometer (AE33 Magee Scientific), spectrofluorometer (sea surface samples, Varian Cary Eclipse), and meteorological sensors. 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 mu-Raman (for the airborne ones) and FTIR (for marine ones); similar results (e.g. polyethylene, polyethylene terephthalates, polyurethane) were found in the two environmental compartments. The concentrations and similar composition in air and sea suggested a linkage between the two compartments. For this purpose, the atmospheric MPs' equivalent aerodynamic diameter was calculated (28 +/- 3 mu m) first showing the capability of atmospheric MPs to remain suspended in the air. At the same time, the computed turnover times (0.3-90 h; depending on MPs size) limited the transport distance range. The estimated MPs sea emission fluxes (4-18 * 10(6) mu m(3) m(-2) s(-1) range) finally showed the contemporary presence of atmospheric transport together with a continuous emission from the sea surface enabling a grasshopper long-range transport of microplastics across the sea.

Automated summary

Microplastics (MPs) pollution is a significant problem on Earth and has been identified in various natural environments. This study examined the concentrations, composition, and transport of atmospheric and marine MPs in the Baltic Sea. The results revealed higher average concentrations of airborne microplastics in the harbor compared to the open sea, but similar compositions were found in both environments. The findings also demonstrated the ability of atmospheric MPs to remain suspended in the air and estimated the emission fluxes from the sea surface, indicating a potential long-range transport of microplastics across the sea.