This study aims to investigate the perturbation mechanisms of street tree morphological characteristics on the near-surface carbon monoxide (CO) concentration distribution at the micro-scale. Based on the L16(45) orthogonal experimental design and numerical simulations, the impacts of four morphological parameters—tree height, branching height, crown spread, and canopy edge distance—on CO concentration were systematically quantified. Range and variance contribution analysis indicate that branching height is the absolute dominant factor governing CO dispersion with a contribution rate of 49.97%, which significantly promotes the dissipation of bottom-level pollutants by expanding the under-canopy clearance. Crown spread, with a contribution rate of 25.58%, exhibits a marginally significant positive correlation with CO concentration due to enhanced aerodynamic resistance, whereas the effect of tree height does not reach statistical significance. Furthermore, by eliminating redundant variables through stepwise regression analysis, a multivariate empirical prediction model for CO concentration (R2 = 0.77) was established, incorporating branching height, crown spread, and canopy edge distance as independent variables. This study reveals the decisive role of under-canopy spatial permeability in regulating the microclimate environment, and provides a solid quantitative basis for the topological optimization of urban green spaces targeting low pollutant retention and the precise selection of street trees.
Wang et al. (Tue,) studied this question.
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