Objective Under the dual pressures of global climate change and rapid urbanization, urban heat island effects and air pollution have become prominent environmental problems, severely affect public health and significantly reduce residents' quality of life. In this context, it is essential to take various measures to improve urban road air quality and thermal environment, such as controlling traffic emissions to reduce source pollution, optimizing urban ventilation design to promote pollutant dispersion and alleviate heat accumulation, setting physical barriers to block pollutant transmission, and rationally configuring vegetation to promote pollutant deposition and provide shading and cooling. Among these, the rational configuration of vegetation has been considered one of the feasible measures to significantly improve road air quality and thermal environment in the short term. However, previous studies have mostly focused on analyzing single ecological benefits, failing to fully reveal the complex coupling relationships between road greenspace vegetation’s improvement of air quality and regulation of thermal environments, as well as the inherent synergistic and antagonistic mechanisms. In particular, there has been a lack of systematic reviews on balancing multiple benefits, evaluating the comprehensive impacts of different vegetation configuration patterns, and understanding the interaction among environmental background factors.

Methods This study constructed a comprehensive analytical framework from three dimensions: vegetation individual traits, community configuration characteristics, and environmental background. It elucidated the synergistic and antagonistic mechanisms of road greenspace vegetation in improving air quality and regulating thermal environments, providing a theoretical basis for road space greening design to promote urban public health and the construction of sustainable living environments.

Results The study demonstrated that road greenspace vegetation had significant multidimensional effects on road environments, with various trade-offs and synergies. 1) Road greenspace vegetation had significant multidimensional effects and trade-offs on road environments. The realization of ecological benefits from vegetation was influenced by the combined effects of micro-scale leaf characteristics (such as epidermal wax, stomatal density, and trichome structure), macro-scale canopy structure (canopy width, leaf area), and community configuration features (stratified structure, planting density). There were complex interactions between different dimensional characteristics: for example, a high leaf area could enhance pollutant deposition and shading effects but might reduce canopy permeability, obstructing pollutant diffusion and leading to increased local pollutant concentrations. Similarly, a lower branch height could expand shading coverage but might inhibit near-surface air circulation, affecting thermal comfort. This cross-dimensional trade-off mechanism indicated that optimal vegetation configuration must be systematically and collaboratively optimized based on specific ecological benefit goals. 2) Road greenspace vegetation exhibited both synergistic and antagonistic effects in improving air quality and regulating thermal environments. High leaf area and high canopy closure vegetation could provide ample shading and transpiration cooling effects, thereby reducing air temperature and mean radiant temperature; however, effective pollutant diffusion required vegetation with appropriate porosity to ensure ventilation efficiency at pedestrian height, avoiding pollutant accumulation. Under ideal conditions, a well-structured stratified community could simultaneously achieve efficient pollutant reduction and effective thermal environment regulation. However, the mechanisms by which road greenspace vegetation improves air quality and regulates thermal environments were fundamentally different: high-density vegetation, while enhancing thermal comfort, tends to obstruct air flow, increass local pollution risks; whereas sparse vegetation configurations, although beneficial for pollutant diffusion, may weaken shading effects and transpiration cooling efficiency. Therefore, the vegetation configuration of road green spaces needed to be optimized based on road pollution levels, local microclimate characteristics, and prevailing meteorological conditions. By fine-tuning the three-dimensional structure of vegetation, air quality and thermal comfort could be enhanced in a synergistic manner. 3) Environmental background factors were critical boundary conditions that determined the effectiveness of vegetation ecological functions. The street aspect ratio determined the flow-field pattern and directly affected pollutant dispersion path; street orientation dictated the distribution of solar radiation and was a major factor influencing the spatial variation of thermal environments; wind field conditions govern the interaction processes between vegetation and the atmosphere. Therefore, vegetation configuration should be designed based on the specific spatial characteristics of the street.

Conclusion Current studies have mostly focused on the impact of two-dimensional vegetation parameters on single environmental effects. Future research should develop a comprehensive quantification system for vegetation’s three-dimensional spatial morphology. Using technologies such as 3D laser scanning and stereophotogrammetric measurements to obtain canopy volume, leaf area density, and other spatial parameters, combined with computational simulation, will help reveal the coupling mechanisms between the three-dimensional spatial structure of road greenspace vegetation, pollutant dispersion, and heat radiation transfer. This will contribute to the development of a road greenspace vegetation design model based on spatial integrity. Furthermore, existing research has paid little attention to the interactive regulation mechanisms between road greenspace vegetation, air quality, and thermal environments. Most studies isolate the analysis of single environmental factors and fail to fully elucidate the synergistic effects of vegetation on the combined processes of pollution and heat. Future research should focus on simultaneous monitoring of canopy microclimates and spatiotemporal dynamics of multiple air pollutants, quantitatively analyzing the coupling relationship between thermal environment and pollution distribution under vegetation structure control, and exploring the synergistic and trade-off mechanisms in improving air quality and regulating thermal environments. This will provide a scientific basis for the creation of healthy and comfortable road space.