Green roofs and green walls layouts for improved urban air quality by mitigating particulate matter

Abstract

Urban air quality has been a long-standing problem in most cities worldwide. Many strategies have been proposed to solve it, including green infrastructures such as green roofs (GRs) and green walls (GWs) that provide multiple environmental benefits. Many studies have focused on GRs and GWs strategies to mitigate urban air pollution. However, to the best of authors’ knowledge, these studies have not dealt with different urban morphologies, specifically the impact of building heights and coverage ratios of GRs and GWs on mitigating air pollution. Therefore, the potential of GRs and GWs to alleviate air pollution has not been fully exploited. This paper aims to investigate different GRs and GWs layouts and evaluate their efficacy for capturing particulate matter (PM2.5) in an urban neighborhood of Santiago, Chile. We use ENVI-met model to simulate a metropolitan area with buildings, vegetation, paved surfaces, and traffic emissions to estimate air pollution abatement for varying building heights and coverage ratios of GRs and GWs. We simulate these layouts and coverage for a downtown area of Santiago, and results were compared with the base case scenario. Results showed that the air quality improvement by GRs and GWs depends on building height, surrounding urban infrastructure, vegetation cover and proximity to the pollutant source. Specifically, results showed that 50%–75% of GRs coverage on low-rise buildings could improve air quality at the pedestrian/commuter level. However, just a 25% coverage of GWs yields the highest PM2.5 capture. We conclude that to decrease PM2.5 concentrations, priority should be given to instal GRs in buildings lower than 10 m in height. For GWs, the PM2.5 abatement is favorable in all cases. ENVI-met results also show that the combined use of GRs and GWs could reduce PM2.5 up to 7.3% in Santiago compared to the base case scenario.