Street canyons restrict natural ventilation flow due to their geometric complexity, and hence cause the increase in air pollution related issues which are detrimental to the health of residents in and around such areas. To mitigate these issues, many research articles explore new designs and how arrange barriers/obstacles to improve roadside air quality and ventilation within the urban street canyon (Gallagher et al., 2015; Huang et al., 2021).

These obstacles are generally categorized into two types – porous and non-porous. Porous barriers include vegetated shrubs and trees, while non-porous barriers include parked cars, low boundary walls, etc (Gallagher et al., 2015). Further categorization includes design strategies that can be applied to new developments or in-street modifications that can be applied to existing street canyons (Huang et al., 2021). These barriers can reduce the air pollution in multiple ways – such as dispersion, deposition and even chemical transformation (in the case of gaseous pollutants) (Abhijith et al., 2017; Druckman et al., 2019). A recent review by Huang et al. (2021) strongly suggests that combining solid and porous barriers offers more potential than individual use. Moreover, new developments can benefit from added design flexibility by the use of lift-up building design and building porosity as a promising way of improving ventilation (Tse et al., 2017).

This paper reviews the different research studies conducted on obstacles/barriers in an urban canyon which helps improve air quality. It shall highlight potential future research avenues, while also pointing out gaps in the research (such as the lack of real-world data experimental validation) that should be addressed going forward.

Abhijith, K. V. et al. (2017) doi: 10.1016/j.atmosenv.2017.05.014

Druckman, A. et al. (2019) doi: 10.1016/j.envint.2019.105181

Gallagher, J. et al. (2015) doi: 10.1016/j.atmosenv.2015.08.075

Huang, Y. et al. (2021) doi: 10.1016/j.envpol.2021.116971

Tse, K. T. et al. (2017) doi: 10.1016/j.buildenv.2017.03.011