Atmospheric deposition of microplastics in the coastal zone: Characteristics and relationship with meteorological factors

In this study, the quantitative and qualitative compositions of microplastics (MPs) deposited from the atmosphere in the coastal zone were analysed. Moreover, links between MP deposition and meteorological factors (air humidity, wind speed, precipitation height, and air mass trajectories) were investigated. MP deposition samples were collected in the southern Baltic area in 2017 and 2018 for 286 days in total. The morphological features of MPs (shape and size) were analysed using a digital microscope. Qualitative analysis was performed using micro-attenuated total reflectance Fourier-transform infrared spectroscopy (μATR FT-IR). The size of the deposited MPs ranged from 5 μm to 5000 μm, and smaller size classes (<720 μm) were predominant (70%). Fibres were of the dominant type (60%). Films and fragments constituted 26% and 14% of the total MPs, respectively, while 55% of the MPs found in the study were polymers often used in textiles, packaging materials, and fishing gear (polyesters and polypropylene). The atmospheric MP deposition ranged from 0 m·d to 30 m·d (average: 10 ± 8 m·d; median: 8 m·d). Based on the air mass trajectory cluster analysis, MPs deposited in Gdynia mainly originated from local sources (<100 km). Furthermore, higher MP deposition occurred when the inflowing air masses were terrestrial, and lower deposition occurred when they were marine. On average, during wet periods twice the amount of MPs was deposited in comparison with dry periods. During dry periods deposition increased with increasing wind speed and was intensified by high relative humidity.