Abstract
Microplastics (MPs) and nanoplastics (NPs) are emerging environmental pollutants, yet their behavior in the atmosphere remains poorly understood. Using an innovative method capable of detecting plastic particles as small as 200 nanometers, we quantified MPs and NPs in aerosols, dry and wet deposition, and resuspension in two Chinese megacities, Guangzhou and Xi'an. Airborne concentrations reached 1.8 × 10(5) MPs per cubic meter and 5.0 × 10(4) NPs per cubic meter in Guangzhou and 1.4 × 10(5) MPs per cubic meter and 3.0 × 10(4) NPs per cubic meter in Xi'an. Estimates revealed a variation of two to five orders of magnitude in MP and NP fluxes across major atmospheric compartments, dominated by road dust resuspension and rainfall-driven wet precipitation. Plastic particles were more heterogeneously mixed in deposition samples than in aerosols and resuspension, indicating enhanced aggregation and removal. These results provide an integrated assessment of MPs and NPs in urban atmospheric processes and offer critical insights into their transformation, fate, and potential implication for climate, ecosystems, and human health.