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 (Pitosporumtobira, Lavandulaangustifolia, Lampranthusspectabillis, Sedumalbum, and Sedumreflexum) for GRs and four species (Apteniacordiflora, Erigeronkarvinskianus, Sedumpalmeri, and Sedumspuriump.) 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.

Green roofs offer a series of benefits to buildings and to the urban environment. Their use in dry climates requires optimizing the choice of their components (i.e., vegetation, substrate and drainage layer) for the specific local climatic conditions, in order to minimize irrigations needs while preserving the attributes of the roof. In this study, we calibrated and validated an existing hydrological model—IHMORS—for the simulation of the hydrological performance of green roofs. Simulated results were compared to experimental data obtained in an outdoor test facility on several green roof specimens, representing a variety of green roofs configurations. IHMORS was able to reasonably predict the soil moisture dynamics for all tested specimens. The specimens of 10 cm depth were the best simulated by the model, while some overestimation was observed during the model validation for the 5 and 20 cm depth specimens. The model was then used to estimate the number of days in which irrigation is needed, as well as analyze the water runoff control performance of all specimens. We related the amount of water retained by the substrate and depth, magnitude and intensity of precipitation event, and the initial substrate moisture. For all events, the lowest runoff coefficient was simulated for the 20 cm specimens. Our study showed the full potential of the model for estimating the water needs and the runoff control performances of different variants of green roofs.