Species-Dependent Particulate Matter Deposition on a Modular Living Wall System Installed on Urban Viaduct Piers

Urban viaduct corridors represent persistent hotspots of traffic-derived particulate matter (PM), yet the performance of modular living wall systems (MLWS) in such environments remains poorly understood. This study investigated species-dependent deposition of fine-sized (≤2.5 µm) and coarse-sized (>2.5–10 µm) particles on an MLWS installed on viaduct piers in Wuhan, China. Four plant species were evaluated at three installation heights (0 m, 1 m, and 2 m) using 36 leaf samples analysed via environmental scanning electron microscopy and ImageJ-based quantification. Hosta plantaginea and Chlorophytum comosum exhibited substantially higher image-derived particle deposition than Bowles mint and Begonia ‘Escargot’. The observed species-level pattern was consistent with qualitative differences in leaf-surface micromorphology, although the contribution of individual traits could not be determined because these traits were not quantitatively measured. Installation height showed a descriptive but non-significant trend in PM deposition (H = 1.545, p = 0.462), with the highest median value observed at 2 m. Adaxial surfaces showed approximately 2.1 times higher deposited particle counts than abaxial surfaces, based on paired Wilcoxon signed-rank testing (Z = 4.399, p < 0.001). Fine-sized particles accounted for over 80% of total deposited particles across all conditions. These findings offer preliminary indications for species selection in MLWS on transport infrastructure, pending multi-seasonal and multi-site validation.