A Multi-Platform Study on Atmospheric Deposition Flux of Microplastics in the East Sea (Sea of Japan)

The atmosphere is recognized as one of the major pathways for microplastics (MPs) transport from land to the ocean. Reducing uncertainties in deposition flux estimates requires an integrated approach that combines temporal variability, evaluated through long-term monitoring at a fixed station, and spatial variability, assessed through mobile observations. In this study, the deposition flux and pollution characteristics of atmospheric microplastics in the East Sea were analyzed through long-term monitoring at a fixed station (Ulleung Island) and mobile observations conducted via a research vessel (R/V Onnuri). From November 2022 to October 2023, the total deposition flux of MPs measured at the fixed station ranged from 43 to 991 n/m²/day, with an average of 209 ± 281 n/m²/day. The average fluxes of dry and wet deposition were 119 ± 165 n/m²/day and 89 ± 120 n/m²/day, respectively. Although dry deposition exhibited a higher average flux than wet deposition, the difference was not statistically significant. Fragments (67.2%) accounted for the majority of MP shape, with the most common size range being 20-100 μm (72.9%). The dominant polymers identified were polypropylene (32.4%), followed by polyester (30.1%) and polyethylene (15.3%). Cluster-mean back trajectory analysis revealed that MPs in the East Sea originated not only from nearby marine sources but also from distant terrestrial air masses. The spatial distribution of MP deposition measured using a mobile platform showed a decreasing deposition flux with increasing distance from land. Smaller MPs were more frequently detected farther from land, along with a higher proportion of fibrous PES. These mobile observation results were consistent with those of MPs observed at a fixed station. These findings are expected to reduce uncertainties in estimating the atmospheric input of MPs into the ocean.

Acknowledgements

This research was supported by 'Land/Sea-based input and fate of microplastics in the marine environment' of Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries, Republic of Korea (RS-2022-KS221604).