Autumnal particulate matter deposition on woody plant leaves reveals trait-based species selection for air pollution mitigation

Autumn-season particulate matter (PM) deposition on urban vegetation remains poorly understood, despite the influence of rainfall, wind variability, and leaf aging on particle retention. This study quantified coarse (10–100 μm), fine (2.5–10 μm), and ultrafine (0.2–2.5 μm) PM fractions accumulated on leaves of three common urban tree species on the Chikushi Campus of Kyushu University (Fukuoka, Japan): the deciduous Acer palmatum Thunb. and the evergreen Toxicodendron succedaneum (L.) Kuntze and Cinnamomum camphora (L.) J.Presl. Leaves were collected during October 2022 in two sampling campaigns separated by 14 days. Deposited PM was extracted by sequential washing (distilled water and 5% SDS) and quantified gravimetrically through stepwise filtration, with deposition expressed per unit leaf area. Leaf surface micro-topography was examined using a 3D laser measuring microscope to relate deposition patterns to leaf traits, and visible stress symptoms were documented for A. palmatum . Apparent species-specific differences were observed in both total PM load and size-selective retention. T. succedaneum showed the greatest capacity to capture health-relevant PM, with fine particles comprising 33% of the total load and ultrafine particles 18%, whereas C. camphora consistently exhibited the lowest retention (fine 13%; ultrafine 6.9%). A. palmatum accumulated moderate total PM (89.9 μg cm −2 ) with dominance of the coarse fraction (41.4%), indicating stronger effectiveness for dust-sized particles rather than the finest fractions. Temporal responses differed by species: PM accumulation increased from the first to the second sampling event in T. succedaneum , while C. camphora decreased, consistent with wash-off and resuspension under repeated wind and rainfall. For A. palmatum , proximity to pollution sources did not predict higher deposition; near-road individuals accumulated less PM than semi-sheltered trees, suggesting that microclimatic exposure (solar radiation, turbulence, precipitation) can outweigh emission proximity during autumn. Leaf surface roughness and grooves enhanced retention, while glossy or leathery surfaces were less efficient for fine and ultrafine particles; A. palmatum also exhibited chlorosis and necrotic spotting, indicating PM-associated stress. Overall, species identity governed PM size selectivity and sampling time reflected a dynamic balance between deposition and removal, ranking mitigation potential as T. succedaneum > A. palmatum > C. camphora . Beyond urban ecology, the results provide a trait-based, application-oriented framework for selecting woody plant species as functional biological materials for particulate pollution control in managed and engineered green systems.