A review of strategies for mitigating roadside air pollution in urban street canyons. (1st July 2021)

• Record Type: Journal Article
• Authors: Huang, Yuhan; Lei, Chengwang; Liu, Chun-Ho; Perez, Pascal; Forehead, Hugh; Kong, Shaofei; Zhou, John L.
• Is Part Of: Environmental pollution. Volume 280(2021)
• Publication Date: 2021-07-01
• Subjects: Roadside air quality -- Urban street canyons -- Vehicle emission dispersion -- Control measures -- Urban planning; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2021.116971
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: Urban street canyons formed by high-rise buildings restrict the dispersion of vehicle emissions, which pose severe health risks to the public by aggravating roadside air quality. However, this issue is often overlooked in city planning. This paper reviews the mechanisms controlling vehicle emission dispersion in urban street canyons and the strategies for managing roadside air pollution. Studies have shown that air pollution hotspots are not all attributed to heavy traffic and proper urban design can mitigate air pollution. The key factors include traffic conditions, canyon geometry, weather conditions and chemical reactions. Two categories of mitigation strategies are identified, namely traffic interventions and city planning. Popular traffic interventions for street canyons include low emission zones and congestion charges which can moderately improve roadside air quality. In comparison, city planning in terms of building geometry can significantly promote pollutant dispersion in street canyons. General design guidelines, such as lower canyon aspect ratio, alignment between streets and prevailing winds, non-uniform building heights and ground-level building porosity, may be encompassed in new development. Concurrently, in-street barriers are widely applicable to rectify the poor roadside air quality in existing street canyons. They are broadly classified into porous (e.g. trees and hedges) and solid (e.g. kerbside parked cars, noise fences and viaducts) barriers that utilize their aerodynamic advantages to ease roadside air pollution. Post-evaluations are needed to review these strategies by real-world field experiments and more detailed modelling in the practical perspective. Graphical abstract: Image 1 Highlights: Key influences are canyon geometry, traffic and weather conditions, and chemical reactions. Traffic interventions in street canyons lead to moderate improvement of roadside air quality. Well-designed canyon geometry significantly enhances dispersion of emissions. Combining solid and porous in-street barriers is more effective than individual use. Traffic control and in-street barriers are more implementable than canyon geometry design.