Comparative study on soot particle resuspension from coniferous and broadleaf urban tree species

초록

Airborne particulate matter (PM), particularly black carbon from vehicle exhaust, poses significant risks to urban air quality and human health. While urban vegetation is known to reduce PM through deposition on leaf surfaces, the resuspension of deposited particles under wind conditions remains insufficiently understood. In this study, the resuspension behavior of soot particles deposited on four tree species commonly planted in South Korea (Metasequoia glyptostroboides, Euonymus japonicus, Pinus densiflora, and Ginkgo biloba) was experimentally investigated using a custom-designed wind tunnel. Soot aerosols generated by a diffusion flame burner exhibited a log-normal size distribution with a peak at 125–130 nm, consistent with diesel exhaust particles. Trees were exposed to soot aerosol for 5 h, followed by clean-air flows at 1, 3, 5, and 7 m/s to simulate urban wind conditions. Results indicated that particle resuspension was most pronounced during the first 20–30 min of clean-air supply, after which concentrations decreased rapidly. Exponential decay functions accurately described the resuspension trends, with decay coefficients increasing with airflow velocity. Broadleaf species (Euonymus japonicus and Ginkgo biloba) exhibited higher decay coefficients than conifers (Metasequoia glyptostroboides and Pinus densiflora), reflecting weaker adhesion on smoother leaf surfaces and stronger leaf fluttering under airflow. Conversely, coniferous species with rough surfaces and dense leaf structures exhibited slower resuspension. These findings confirm that leaf structural traits significantly influence resuspension processes. It is therefore suggested that, in urban greening strategies, the potential for particle resuspension should be considered together with deposition capacity to maximize the air-quality benefits of vegetation.

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