Abstract: Mitigating the adverse effects of air pollution, especially on human health, is one of the greater contemporary challenges for cities. Street canyons have herein been identified as bottleneck areas in urbanized environments. Focusing on the necessity of fast-response interventions, strategies to control source-receptor pathways (e.g. implementing low boundary walls (LBWs)) are gaining interest. A potential strategy which is greatly overlooked is the adjustment (reduction or displacement) of traffic lanes in order to increase the distance between source (traffic) and recipient (pedestrians). Within our study, computation fluid dynamics (CFD) is used to simulate the impact of alternations to traffic lanes (whether or not combined with LBWs) on the pedestrian exposure to NO2 for a specific case-study (Belgie center dot lei, Antwerp) under two prevailing wind directions. The average differences in NO2 concentrations for the entire pedestrian area ranged between +1.0 % to-3.6 %. On specific locations, reduction up to-8.0 % were reached. In case of perpendicular winds, a lateral displacement of all traffic lanes towards the windward facade including LBWs was found most beneficial to reduce pedestrian exposure. LBWs also showed to be efficient in reducing potential adverse effects of lane displacement under less frequent wind directions.

Abstract: Recent studies indicate the necessity of addressing traffic-related air pollution in urban environments, as street canyons are known for their lack of natural ventilation and increased pollution levels. To address this issue, numerous studies have been conducted on different aspects (e.g. aspect ratio, orientation and height variation) and their impact on ventilation and pollution dispersion/dilution performance in street canyons. Despite the numerous studies, the information remains fragmented and the results and applications are fairly unknown in urban planning. Broad review studies on numerous street canyon aspects are also quite scarce. In this study, over 200 studies were collected and reviewed across various parameters and on different configuration levels (street canyon configuration / building configuration / in-canyon configuration). Hereby, the study aims to give a comprehensive overview and to formulate spatial guidelines to improve the application of the reviewed studies for the purpose of urban planning. In total, 19 general guidelines were formulated, and an implementation strategy for the purpose of urban planning was developed. Despite the usability of these guidelines for urban planning, a high number of limitations and variabilities were detected. The broad literature review also revealed knowledge gaps, indicating the potentials for further research.