Effects of building roof greening on air quality in street canyons

• Published in: Atmospheric environment (1994) 2012-12, Vol.61, p.48-55
• Main Authors: Baik, Jong-Jin, Kwak, Kyung-Hwan, Park, Seung-Bu, Ryu, Young-Hee
• Format: Article
• Language: English
• Subjects: air; Air quality; Applied sciences; atmospheric chemistry; Atmospheric pollution; Building roof greening; CFD model; Computational fluid dynamics; Cooling; energy balance; equations; Exact sciences and technology; fluid mechanics; green roofs; Mathematical models; photochemistry; Pollutants; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Roads; Roofs; Street canyon; Street canyons; wind direction
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2012.06.076

Building roof greening is a successful strategy for improving urban thermal environment. It is of theoretical interest and practical importance to study the effects of building roof greening on urban air quality in a systematic and quantitative way. In this study, we examine the effects of building roof greening on air quality in street canyons using a computational fluid dynamics (CFD) model that includes the thermodynamic energy equation and the transport equation of passive, non-reactive pollutants. For simplicity, building roof greening is represented by specified cooling. Results for a simple building configuration with a street canyon aspect ratio of one show that the cool air produced due to building roof greening flows into the street canyon, giving rise to strengthened street canyon flow. The strengthened street canyon flow enhances pollutant dispersion near the road, which decreases pollutant concentration there. Thus, building roof greening improves air quality near the road. The degree of air quality improvement near the road increases as the cooling intensity increases. In the middle region of the street canyon, the air quality can worsen when the cooling intensity is not too strong. Results for a real urban morphology also show that building roof greening improves air quality near roads. The degree of air quality improvement near roads due to building roof greening depends on the ambient wind direction. These findings provide a theoretical foundation for constructing green roofs for the purpose of improving air quality near roads or at a pedestrian level as well as urban thermal environment. Further studies using a CFD model coupled with a photochemistry model and a surface energy balance model are required to evaluate the effects of building roof greening on air quality in street canyons in a more realistic framework. ► Building roof greening effects on air quality in street canyons are examined. ► Building roof greening is represented by specified cooling. ► Building roof greening improves near-road air quality. ► The degree of near-road air quality improvement increases as the cooling is strong. ► The degree of near-road air quality improvement depends on ambient wind direction.