Passive barriers for improved air quality in pedestrian zones at adult and child breathing height

Pedestrians are increasingly affected by air pollution, primarily due to vehicular emissions in densely populated areas. This issue motivates the exploration of passive solutions to improve air quality in pedestrian zones at heights relevant to adults and children. Existing literature indicates a significant gap in understanding the effectiveness of low lying barrier configurations in mitigating pollutant concentrations within pedestrian zones. This study aims to address this gap by investigating the impact of different barrier designs at both adult and child breathing levels and to asses whether their inclusion applies to both the leeward and the windward pedestrian zones. We employed a Computational Fluid Dynamics (CFD) methodology, validated with site measurements, to simulate the aerodynamic effects of various barrier configurations on gaseous (NO 2 ) pollutant dispersion in a typical urban street canyon. The barriers examined include fully vegetative, mixed solid-vegetative barriers and their segmented variants. Key results from our simulations indicate that fully vegetative barriers significantly reduce pollutant concentrations at both child and adult breathing heights by 70% and 50%, while partly solid barriers cause stagnation points that are detrimental particularly to children. The impact of this research is particularly relevant to urban planners seeking to implement effective green infrastructure in street canyon-like urban zones. • Fully vegetative low lying barriers reduce urban air pollutants effectively. • Partly solid barriers hinder airflow, trapping pollutants particularly at child breathing heights. • The placement of vegetative barriers should be on the leeward pedestrian zone.