Quantifying Morphological Complexity and Wet Deposition of Microplastics Abundance: A Case Study of Wroclaw, Poland

Despite growing concern regarding the wet deposition of atmospheric microplastics (MPs), the role of particle morphological complexity in controlling deposition efficiency and atmospheric transport remains insufficiently understood. Characterising MP geometry is essential for analysing aerodynamic behaviour and environmental interactions. This study presents the first quantitative assessment of the fractal dimension (FD) of microplastics deposited via rainfall in Central Europe. Over a 14‑month period, rainwater samples were collected from urban residential and traffic‑influenced areas in Wroclaw, Poland, using a passive sampler positioned 5 m above ground level. Advanced morphological characterisation was conducted using scanning electron microscopy (SEM), followed by vector‑based geometric analysis implemented in Python for particle classification and FD estimation. Mean MP abundances were 135 ± 89 particles L⁻¹ in the residential area and 168 ± 64 particles L⁻¹ in the traffic‑influenced area. Fibres dominated wet deposition and exhibited a narrow FD range (1.10 ± 0.15), indicating smooth, elongated geometries with low structural complexity. Fragments were observed less frequently and showed greater morphological variability; however, the analysis focuses primarily on fibres because they are more common. These findings demonstrate that fractal dimension provides a quantitative descriptor of microplastic morphological complexity and may serve as an indicator of aerodynamic behaviour and environmental fate in atmospheric systems.