Wet and dry atmospheric deposition of microplastics in Switzerland

Microplastics (MPs) are contaminants of global concern, and the atmosphere plays an important role in distributing these contaminants in the environment.¹ We developed a tailored analytical chain – including sample collection, processing, and analysis based on optical microscopy and focal plane array μ-Fourier transform infrared spectroscopy (FPA-μ-FTIR) – to quantify MPs (20-215 μm) in wet and dry atmospheric deposition.² As part of the sampling setup, an on-site precipitation filtration device was developed to collect particulate wet deposition. An assessment of the total measurement uncertainty was performed, taking into account each individual step of the analytical chain. The resulting total expanded uncertainty was approximately 90% for determining MP numbers in a single wet or dry deposition sample. The conversion of MP numbers and associated size information into MP mass was estimated to generate an additional systematic error of 50%.

The analytical chain developed was used in a one-year monitoring study of atmospheric deposition of MPs in Switzerland. Specifically, we collected wet and dry deposition samples at five stations in Switzerland, including one urban, one suburban, two rural and one mountainous site, on a four-weekly basis. Based on the analysis of these samples, we determined the wet and dry deposition rates at each site both in terms of the number of MPs and MP mass. To put the determined deposition rates into context, we compared the deposition rates of MPs to those of total aerosols or dust as well as of tire wear particles, which were measured in parallel partner projects at the same or similar sites. The sizes and polymer types of MPs found in atmospheric deposition samples are reported. Finally, based on the MP mass deposition at the different sites and land-use statistics in Switzerland, we estimated the total annual deposition of MPs (including tire wear) across Switzerland, including an estimation of MP inputs from the atmosphere to soil and water. We found that the atmospheric deposition of tire wear in Switzerland is by mass about one order of magnitude higher than that of other synthetic polymers.

 

References

(1) Brahney, J.; Mahowald, N.; Prank, M.; Cornwell, G.; Klimont, Z.; Matsui, H.; Prather, K. A. Constraining the Atmospheric Limb of the Plastic Cycle. Proc. Natl. Acad. Sci. 2021, 118 (16), e2020719118. https://doi.org/10.1073/pnas.2020719118.

(2) Ashta, N. M.; Crosset-Perrotin, G.; Moraz, A.; Stoffel, J.; Schilt, U.; Ceglie, E.; Schoenenberger, D.; Philipp, M.; Bucheli, T. D.; Kaegi, R.; Hueglin, C. Atmospheric Deposition of Microplastics: A Sampling and Analytical Method Including the Associated Measurement Uncertainties. EGUsphere 2025, 2025, 1–30. https://doi.org/10.5194/egusphere-2025-4786.