Wet and dry atmospheric deposition of microplastics at urban, suburban, rural and mountainous sites in Switzerland

Abstract. Microplastics (MPs) are environmental contaminants of global concern. Although the relevance of the atmosphere in the transport and distribution of MPs worldwide has been acknowledged, country-scale quantitative data on wet and dry MP deposition rates remain limited. We therefore quantified MPs in wet and dry atmospheric deposition samples collected on a four-weekly basis over a one-year period between May 2024 and May 2025 at one urban (Zurich), one suburban (Duebendorf), two rural (Magadino and Payerne) and one mountainous site (Chaumont) in Switzerland. We used focal plane array µ-Fourier transform infrared spectroscopy to identify MPs in the 20–215 μm size range and included a rigorous assessment of the measurement uncertainties. Particle sizes were converted into masses to obtain mass deposition rates. The number- and mass-based MP deposition rates were highest at the urban site, with respective means of 881 MPs m⁻² d⁻¹ [95% confidence interval (CI): 562–1199] and 53 μg m⁻² d⁻¹ [CI: 17–107]. The deposition rates were lower and similar among the remaining sites, ranging from 249 to 331 MPs m⁻² d⁻¹ [CI: 140–478] and from 13 to 21 μg m⁻² d⁻¹ [CI: 4–46]. Based on the determined deposition rates and land-use statistics, an annual MP deposition of 219 tonnes or 3.8·10¹⁴ particles was estimated for regions < 2000 m above sea level across Switzerland. Annual atmospheric inputs of MPs to Swiss agricultural land and surface waters were estimated at 78 and 10 tonnes, respectively.