Combined efficiency of tree and shrub vegetation barriers in mitigating PM, TEs, and PAHs along urban roadways

Urbanization and increasing vehicular traffic have intensified air pollution, particularly the accumulation of particulate matter (PM), trace elements (TEs), and polycyclic aromatic hydrocarbons (PAHs) in urban environments. These pollutants pose significant risks to human health, urban ecosystems, and biodiversity. This study evaluates the efficacy of mixed-species vegetation barriers, comprising Betula pendula, Quercus robur, Physocarpus opulifolius, and Sorbaria sorbifolia, in mitigating air pollution along three road types (highway, urban, and suburban). Using Tilia cordata as a bioindicator, PM deposition across three size fractions (10-100, 2.5-10, and 0.2-2.5 µm) as well as TEs and PAH concentrations were analyzed. Results revealed significant variation in pollutant accumulation across species, barrier types, and locations. Shrubs captured up to 12% more PM than trees, and vegetation barriers reduced large PM by approximately 50% behind the barrier at highway sites. Concentrations of TEs and PAHs were highest near high-traffic roads, especially in tree foliage, with values decreasing in less polluted areas. These findings highlight the importance of strategic plant species selection, barrier composition, and design in urban greening initiatives aimed at combating air pollution and enhancing public health and ecological resilience.