| 18 May 2026
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.
The revised paper addressed my comments and paper can be published after addressing my further comment outlined below:
While the paper explicitly states that tire-wear particles were excluded and that “MPs” means microplastics excluding tire-wear particles, a concern still need to be raided. Tire-wear particles are widely considered one of the dominant sources of environmental microplastic pollution. Therefore, excluding them can substantially bias mass-based MP deposition flux downward. The bias may be less predictable for particle number, because tire-wear particles have complex size distributions and many may be below the paper’s 20 µm detection limit. The exclusion of tire-wear particles, the 20–215 µm analytical window, and the conversion of 2D particle images to mass mean that the reported mass fluxes should not be interpreted as total atmospheric plastic-particle deposition. The underestimation is likely most serious for urban environments and for mass-based fluxes. The authors should state more prominently in Abstract and Conclusion that their 219 tonnes yr⁻¹ estimate excludes tire-wear particles, particles <20 µm, particles >215 µm, and high-altitude areas >2000 m.