Abstract: With the development of high-density and high-rise buildings on both sides of the street, widespread attention has been paid to the applicability of the traditional greening model of ‘the more trees, the better atmospheric environment' in dealing with air pollution in urban street canyons. Clarifying the characteristics of street canyons greening and its planting design pattern on the reduction of emission pollutants by vehicles is an important prerequisite for the improvement of air quality in the street canyons. Based on literature review, we compared the applicability and limitations of the three methods, including field observation, wind tunnel test, and numerical simulation. We further analyzed the effects of roadside trees and hedges on the dispersion and deposition of air pollutants, and put forward a framework of adaptive greening design for air quality improvement. Finally, we proposed that future studies should address the creation of graphic languages for roadside greening design, the development of technical guidelines for evaluating the exposure of air pollution, and the optimization of parameterization schemes for the physical processes of greening effect in computational fluid dynamics models. Overall, our review could provide ideas and reference for the subsequent research.

Key words: street canyon, vehicle emission, roadside tree, hedge, dispersion, deposition, planting design