Above and Beyond: The Journey and Persistence of Micro- and Nanoplastics in the Atmosphere

Plastic pollution, a pervasive global challenge, necessitates a nuanced understanding of micro- and nanoplastic (MNP) transport and transformation dynamics in the atmosphere, to predict residence times and assess their potential for long-range atmospheric transport under different meteorological conditions. This study intricately examines MNP transport mechanisms and residence times, accounting for diverse compositional, dimensional, and meteorological variables. Ranging from 1 nm to 5 mm, MNPs present unique complexities, particularly in tropospheric transport and deposition; and existing transport models for atmospheric particles (e.g. dust, ash or pollen) cannot be directly applied to the entire MNP range. MNPs demand dedicated or adapted equations and parameters, a necessity heightened by non-spherical shapes and complexities arising for aggregated MNPs.

Addressing the dynamic size and shape spectrum of MNPs, this study theoretically investigates and advances the description of different deposition processes: dry settling, and resistance deposition near surfaces, wet deposition during precipitation events. For each process, the impact of MNPs sizes, densities and shapes are assessed and compared to meteorological or other environmental influences (e.g. wind surface speed, rain intensity, deposition surface properties).

- Dry Settling: Exploring dry settling reveals size, density, weathering, shape, and aggregation impacts on MNP behavior.

- Dry Deposition: Here the influence of land surface characteristics and atmospheric stratification are dissected, refining theoretical foundations.

- Wet Scavenging: Scrutinizing below-cloud and in-cloud processes, these investigations unravel intricate mechanisms of particle capture during precipitation events.

Finally, we combine the above processes to determine the total residence times of MNPs in the atmosphere under selected meteorological scenarios. This research augments current theoretical frameworks for predicting atmospheric transport of MNPs, providing valuable process description for environmental fate models and directives for monitoring efforts. A systematic exploration of MNP characteristics and environmental conditions enhances our scientific comprehension of atmospheric MNP transport, supplying essential insights for refining transport models and steering future investigations.