Wet and Dry Deposition Flux Measurements of Atmospheric Microplastic Particles in Central Germany

Abstract Air emissions, atmospheric transport and subsequent deposition of microplastics to other environments are now recognized. However, atmospheric dry and wet deposition of plastic particles and how different weather conditions may affect this fallout process are still poorly investigated. Hence, we examined wet and dry deposition of airborne plastic particulates from the atmosphere at a site in Kassel in Central Germany. Monthly samples of wet and dry deposition were taken separately over one year (05/2019-05/2020) and analysed by micro-Fourier-Transform Infrared spectroscopy (µFTIR) down to 11 µm. Additionally, one exemplary dry deposition sample was subjected to Raman analyses to investigate the abundance of dry deposited plastic particles in the lower micron and submicron size range. Microplastic particles in size range of 11 µm to 130 µm were detected in all wet deposition samples and in 5 out of 12 dry deposition samples by µFTIR. Polypropylene particles were found most frequently and accounted for 62% and 54% of all particles in wet and dry deposition, respectively. Wet deposition of plastics dominated at the study site and comprised 62% of the total number and 70% of the total mass of deposition. Plastic wet deposition fluxes (DFs) were 10 ± 5 MPs m− 2 day− 1 and accounted for 4284 MPs m− 2 a− 1. Microplastic deposition was elevated when the dominant wind direction was recorded in the direction from the city centre of Kassel and concentrations in precipitation correlated significantly with population-weighted air mass trajectories. Thus, anthropogenic activities contribute to the MP pollution at the study site. Raman analyses revealed additional plastic particles in the micron (> 10 µm) and lower micron (between 10 µm and 1 µm) range but submicron (< 1 µm) range particles made of common synthetic polymer materials could not be detected in the exemplary analysed dry deposition sample. Our results suggest that microplastic analysis by µFTIR down to 11 µm may underestimate DFs at least by an order of magnitude. However, more comprehensive studies on submicroplastics and nanoplastics (< 100 nm) are needed to fully assess air pollution by plastic particles.