Mitigating particulate matter through building-integrated greenery with active airflow: experimental validation and CFD modeling

Abstract

Urban or building-integrated greenery systems represent a promising Nature-based Solution for mitigating local particulate matter concentrations. However, field investigations concerning real-world PM filtration by hedges at building air intakes remain rare due to environmental complexities and the highly specific nature of each application. This study evaluates the PM mitigation performance of an active, hedge-based filtration system integrated into a building's HVAC intake through a hybrid approach combining an in-situ monitoring campaign and computational fluid dynamics modeling. The empirical results demonstrate localized filtration potential, with median reductions of 23.2% for PM2.5 and 24.4% for PM10 directly behind the vegetation. Considering air stream bypass, reductions at the air intake were observed for 10.6% and 13.1% for PM2.5 and PM10, respectively. The computational fluid dynamics model exhibited discrepancies of 6.48% for PM2.5 and 8.98% for PM10 compared to empirical data. Parametric simulations varying leaf area density and geometric configurations indicated that aerodynamic resistance limits structural flow when leaf area density exceeds 3.0 m2/m3. By optimizing the geometric interface to achieve less bypass, simulated system efficiency was maximized to 17.1%. While building-integrated active greenery cannot replace mechanical HVAC filters, it could possibly serve as a pre-filtration stage under the of requirements of strategic geometric configuration, optimized leaf area density and appropriate choice of plant species.