Integrated vegetation effects on thermal environment and air quality in urban street canyons

Abstract

Climate change and rapid urbanization exacerbate urban environmental challenges, particularly the urban heat island effect (UHI) and air pollution. Urban street canyons are critical hotspots for both heat stress and traffic-related pollution. This thermo-pollutant coupling threatens public health, increases building energy consumption and carbon emissions, and hinders urban sustainability. Moving beyond single-pollutant approaches, this study proposed a nature-based solution integrating vertical greening with street trees. Utilizing a validated 3D street canyon multi-field coupling model, we analyzed thermal and pollution distributions under three scenarios: no greenery, street trees only, and street trees combined with vertical greenery. Computational fluid dynamics (CFD) simulations quantified vegetation impacts on wind flow, temperature distribution, and particle deposition, elucidating the regulatory mechanisms. Results demonstrated the high efficacy of integrated vegetation in co-mitigating heat and pollution. Street trees alone reduced near-building temperatures by an average of 0.2 °C through shading and transpiration. Adding vertical greenery enhanced cooling by up to 0.6 °C and promoted more uniform temperature distribution. For air pollution control, the combined system achieved a remarkable 95 % particle removal rate, significantly outperforming street trees alone (71 %) and reducing vertical pollution stratification. This study provides critical insights for urban nature-based design and offers a vegetation configuration paradigm for high-density streets to maximize environmental co-benefits. By addressing the coupled thermo-pollutant challenge, it can help enhance understanding of greening's regulatory role in complex urban systems and support sustainable urban development.