Urban trees as natural interceptors for aerial microplastics: Mechanisms, influencing factors, and selection of tree types for mitigation.

Urban trees have gained significant scientific attention for their role in mitigating aerial microplastic (AMP) pollution through natural interception mechanisms. This study aims to provide a comprehensive understanding of the characteristics and sources of urban AMPs, with their interception mechanisms by trees, influencing factors, tree type selection for mitigation, and potential nature-based solutions for reducing urban-AMP pollution. The prevalence of AMPs in urban air primarily originates from industrial emissions, vehicular activity, landfills, agricultural practices, and marine wave action. Urban trees and their associated components (e.g., moss, lichen, and spider webs) intercept AMPs through π-π bonding, weak hydrophobic interactions, and adhesion. Our meta-analysis revealed that fiber-shaped (100 %) with sizes <1 mm (58.33 %) and polypropylene (83.33 %) were the most frequently observed AMP type on leaf surfaces. Among tree species, Photinia glabra intercepted the highest diversity of polymers (16 types). AMP interception was predominantly influenced by wind actions, rainfall, leaf microstructure, and overall tree health. Notably, rainfall removes AMPs from leaf surfaces, facilitating continuous interception cycles and reducing health risks. Furthermore, statistical analysis showed significant variations (p < 0.05) in AMP concentrations between plant types (angiosperms vs. gymnosperms); although, no significant differences observed in AMP concentration or polymer type when comparing foliar phenology (evergreen vs. deciduous) or foliage type (broadleaf vs. needle-shaped/conifer). Nonetheless, considering the broad geographic distribution and perennial presence, indigenous-evergreen trees emerge as optimal choices for mitigating urban AMP pollution. Additionally, principal component analysis (PCA) revealed that tree height and leaf length-to-width ratio is associated with AMP concentration and polymer type in evergreen trees. These findings re-establish the selection of indigenous-evergreen species as the most effective tree group for urban AMP mitigation. Finally, we recommend a strategic plantation of indigenous-evergreen trees in key urban areas, such as roadsides, landfills, children's parks, Miyawaki forests and urban-mangrove areas to reduce AMP pollution.