The magnitude and patterns of atmospheric microplastic deposition rates are crucial factors for calculating the input of microplastics in the environment. Nevertheless, long-term and spatially diverse studies are scarce. In this study, the spatial distribution of atmospheric microplastic particles in urban, sub-urban and rural areas of Northern Germany was investigated in cooperation with the Hamburg Luftmessnetz and as part of the MICROLIM project (German Research Foundation, DFG). Therefore, eleven structurally diverse locations in Hamburg and Mecklenburg-Western Pomerania were equipped with bulk-deposition samplers in triplicates and sampled monthly between August 2019 and July 2020. The resulting 306 samples were treated with hydrogen peroxide (30%) and sodium hypochlorite (6-14%) to digest biological organic matter. The filters were subsequently stained with the lipophilic dye Nile Red (1 mg/ml in chloroform) and underwent microplastic identification via fluorescence microscopy (Axioscope 7, Zeiss). A subset of particles identified as synthetic particles were analysed for their composition using μRaman spectroscopy (DXR2xi Raman Imaging Microscope, Thermo Fisher Scientific). Particles and fibers were quantified down to a cut-off size of 10 µm. The results were compared to the small-scale meteorological data recorded at each investigation site. The study shows that the microplastic deposition rate for Northern Germany (89 ± 61 MP/m²/day) is in the same order of magnitude as those reported by previous studies. Significant differences in microplastic deposition rates and particle morphology were found between urban, sub-urban and rural sampling sites. Population density was identified as an important factor for larger amounts of microplastics and higher shares of fibers in urban samples. Special attention was given to the canopy cover at two forested sampling sites. Sampling throughout the leaf-bearing and leafless period revealed an influence of the comb-out effect on atmospheric microplastic deposition rates for deciduous forests.
Spatial distribution of atmospheric microplastics in bulk deposition of urban and rural environments of Northern Germany
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