Tree Leaf Morphology Shapes Particulate Matter Retention and Wash-off Dynamics under Simulated Rainfall

Urban vegetation mitigates air pollution by capturing particulate matter (PM) on leaf surfaces, yet rainfall can wash away accumulated particles, reducing retention efficiency.This study investigates how leaf morphological traits of ten tree species influence PM accumulation and retention under simulated rainfall.PM was categorized as rain-washable ( RW PM), surface-bound ( S PM), and wax-embedded ( W PM), with the sum of S PM and W PM defined as rain-indelible PM ( RI PM), reflecting long-term retention on leaves.Species varied significantly in PM accumulation.Taxodium distichum, Paulownia tomentosa, and Araucaria araucana showed the highest total PM, while Platanus × acerifolia and Indesia polycarpa showed the lowest.RI PM was most abundant in A. araucana, T. plicata, and P. tomentosa.Total PM correlated positively with foliage type (r = 0.57) and negatively with petiole length (r = -0.59).Higher epicuticular wax content improved fine PM retention, emphasizing the role of chemical traits.In contrast, smooth-leaved species retained less PM, likely due to lower surface roughness.These findings highlight how both structural and biochemical leaf characteristics affect PM capture and retention.They offer valuable insight for selecting tree species in urban planning to enhance air pollution mitigation and contribute to healthier urban environments.