Towards an experimental approach for measuring the removal of urban air pollutants by green roofs

Abstract

Green roofs are a promising approach to mitigate air pollution in urban environments, but limited experimental data is yet available. In this study, we developed a laboratory-scale setup to measure the removal nitrogen dioxide (NO 2 ) and ozone (O 3 ) using a variety of common green roof species.Experiments were conducted on detached leaves and whole plants using two chambers (0.6 L and 12 L), visible lighting, NOx/O 3 sources and online analyzers. Three species were the best performant (Thymus vulgaris, Sedum sexangulare and Heuchera Americana L.) with deposition velocities ranging from 1.6 to 4.82 m/h for NO 2 , and 1.7 to 5.56 m/h for O 3 . In both cases, thyme was the most effective plant likely due to its higher stomatal area and the reactivity of its volatile metabolites with O 3 leading to several oxidized by-products. Furthermore, NO 2 uptake was found to be enhanced by surface water released by leaf transpiration leading to the production of nitrous acid (HONO). Similar values of were observed (3.84 -4.65 m/h) when whole thyme plant was used. The soil was also found to be competitive in removing O 3 but less performant in capturing NO 2 . Using a dry deposition model, we estimated that the three plant species can uptake up to 9 kg/ha/year of NO 2 and 13.6 kg/ha/year, which fall in agreement with previously reported modeling data. Our experimental approach can be a rapid tool for screening the depollution performances of green roof species enabling an effective prioritization for deployment in urban environments.

Environmental and Social Benefits of Extensive Green Roofs Applied on Bus Shelters in Edinburgh

“…The performance of GR and the pollution level are highly dependent on many factors. These include climate, seasonality, vegetation types and biodiversity, aerosol chemistry, leaf morphology, canopy structure, or distance from the road [79][80][81], which need to be considered in further studies. For example, air pollution in urban areas of the Northern Hemisphere is more likely to form in winter due to increased heating, related emissions, and atmospheric inversions.…”

“…Only a few studies are repeatedly cited throughout the available literature, and those are Pugh et al [83], Currie and Bass [33], and Yang et al [56]. However, these heavily rely on modelling and deposition velocities estimation, all based on values not determined for GRs [80,84]. Additionally, the pollution saturation point of GRs is unknown due to the lack of research.…”

Characterisation of the acoustic impedance of vegetated roofs with a multiple-geometry approach

“…Urban air pollution can be mitigated by green walls or green roofs, where the depollution performance of urban vegetation is dependent on building height, vegetation species, vegetation layouts, etc. [11][12][13]. Moreover, the installation of green roofs is a nature-based solution to mitigate flood generation, extreme rainfall effect, etc.…”