Morphology-Dependent Transport of Atmospheric Microplastics and the Indicator Role of Polyester Fibers across the Estuarine- Offshore Gradient.

The atmosphere is an important route for the transport of terrestrial microplastics (MPs) from land to sea, but research on the extent of atmospheric MP transport is limited due to sampling and quantification challenges. Here we focused on a typical land-sea interface, the Yangtze River Estuary, to investigate the transport characteristics and deposition flux of atmospheric MPs. Results show that the particle abundance and mass concentration were 0.03 ± 0.02 item/m3 and 0.01 ± 0.02 μg/m3, respectively. No significant spatial or seasonal (summer, autumn and winter) variation was found, indicating a stable distribution pattern. The atmospheric deposition flux of MPs above the Yangtze River Estuary was estimated to be 0.04 ± 0.08 t/yr. Of note, morphology was found to be an important factor controlling their distribution and transport potential. By using a shape-dependent drag model, we estimated the settling velocities for different non-spherical MPs. Fibers, which account for 90.19% of all MPs, exhibited a relatively lower settling velocity (∼0.05 m/s), indicating high atmospheric transport capability from land to sea. In contrast, non-fibrous MPs showed substantially higher settling velocities (∼0.75 m/s) and a corresponding decline in abundance from inner to offshore regions. Across the estuarine gradient, fibrous polyester MPs were found in consistent abundance, suggesting they can record background atmospheric MP pollution levels and could contribute as reliable evidence required for plastic pollution management and the development of a global plastics treaty.