Potential of particle matter dry deposition on green roofs and living walls vegetation for mitigating urban atmospheric pollution in semiarid climates

In the last two decades, the incorporation of green roofs and living walls in buildings has increased significantly worldwide because of their benefits such as building energy savings, promoting biodiversity, controlling water run-off, mitigating urban heat island effect, improving indoor and urban air quality, and connecting people with nature. However, few studies have quantified the impact of green roofs (GRs) and living walls (LWs) on mitigating air pollution, especially in semiarid climates where airborne particle matter (PM) levels are high. Therefore, the aim of this paper is quantifying the dry deposition of PM₁₀ and PM_2.5 by several vegetation species commonly used in GRs and LWs in semiarid climates. Five species (Pitosporum tobira, Lavandula angustifolia, Lampranthus spectabillis, Sedum album, and Sedum reflexum) for GRs and four species (Aptenia cordiflora, Erigeron karvinskianus, Sedum palmeri, and Sedum spurium p.) for LWs were tested in an experimental facility-through washing, filtering, and weighing-to quantify the dry deposition of PM_2.5 and PM₁₀ on vegetation leaves as well as PM captured by the leaf wax. The main result is that a significant amount of PM is deposited on the typical vegetation used in GRs and LWs in semiarid climates. However, large differences in PM dry deposition were found among species, ranging from 0.09 μg/cm²·h^-1 to 1.32 μg/cm²·h^-1 for PM_2.5, 0.48 μg/cm²·h^-1 to 4.7 μg/cm²·h^-1 for PM₁₀ and 0.41 μg/cm²·h^-1 to 25.6 μg/cm²·h^-1 for leaf wax. The species that showed the highest potential to capture PM were S. album, S. reflexum, S. palmeri, and L. spectabillis. This study shows this green infrastructures can contribute to mitigate air pollution, thus GRs and LWs have the potential for being included in decontamination plans.