Zhengyang Yue, Xuyi Zhang
Introduction Atmospheric PM 2.5 poses significant threats to human health and ecosystems. Vegetation serves as a nature-based solution for mitigating PM 2.5 pollution. While leaf and branch retention capacities have been extensively studied, the role of twigs remains poorly understood. This study evaluated the dry deposition velocities (Vd) of PM 2.5 for twigs, detached leaves, and defoliated branches of Camphora officinarum (broadleaved) and Cedrus deodara (coniferous) under controlled conditions to establish baseline organ-level deposition capacities. Methods Twig samples were collected from three replicate trees per species. Each twig was divided into intact twig, detached leaves, and defoliated branch. Vd was measured in a sealed smog chamber (0.4 m 3 ) at 25°C, 50% relative humidity, and 0.3 m s −1 wind speed using ammonium sulfate particles (500 μg m −3 ). Results For C. officinarum , defoliated branches exhibited the highest Vd (3.16 ± 0.76 cm s −1 ), followed by detached leaves (0.68 ± 0.10 cm s −1 ) and intact twigs (0.60 ± 0.16 cm s −1 ). A similar pattern was observed for C. deodara , with defoliated branches showing the highest Vd (21.18 ± 8.11 cm s −1 ), followed by detached leaves (1.89 ± 0.95 cm s −1 ) and intact twigs (0.61 ± 0.17 cm s −1 ). Branches had significantly higher Vd than leaves and twigs within both species ( p < 0.01 for both). C. deodara exhibited significantly higher Vd than C. officinarum for branches ( p = 0.018) and leaves ( p = 0.049). The surface-area-to-enveloped-space ratio was higher for C. deodara (1.40 ± 0.02 cm −1 ) than C. officinarum (0.61 ± 0.02 cm −1 ) ( p < 0.001). Discussion Defoliated branches exhibited the highest organ-level Vd, followed by detached leaves and twigs. C. deodara showed higher Vd than C. officinarum . However, these findings represent baseline organ-level capacities rather than whole-plant performance, providing foundational insights for future canopy-scale studies.