Impact of roadside vegetation growth on air pollution mitigation
Citation:
Hashad, K., B. Yang, J. Gallagher, R. Baldauf, P. Deshmukh, AND M. Zhang. Impact of roadside vegetation growth on air pollution mitigation. LANDSCAPE AND URBAN PLANNING. Elsevier Science Ltd, New York, NY, 229:0, (2023).
Impact/Purpose:
Exposures to traffic emissions near roadways has been identified as a major public health concern. Roadside vegetation has been shown to reduce air pollution near roads. This paper examines how tree growth can change over time and affect near road air quality. This information will be useful for urban planners and foresters implementing roadside vegetation barrier projects
Description:
As a Nature-Based Solution, roadside green infrastructure (also known as roadside barriers) can potentially mitigate traffic-related air pollution by increasing dispersion and promoting pollutant deposition. For new and existing barriers, the vegetation’s physical and ecological attributes (dimensions and density) are dynamic in nature, and thus affect the barriers’ pollution reduction capabilities. In this study, we first synthesized the results from existing field measurements highlighting the properties of coniferous vegetation, showing that its growth was characterized by an increase in height and a decrease in density. Motivated by this finding, we then conducted 75 simulations using a coupled aerodynamics and deposition model to investigate how the growth patterns of roadside vegetation barriers (e.g., heights from 2-10 m, and leaf area index from 4-11) affects air pollutant reduction under different urban conditions (wind speeds 1-5 ms−1). The coupled aerodynamics and deposition model accounts for the vegetation’s drag, turbulence interaction, and pollutant deposition and was evaluated against two independent field measurements to ensure that it properly captures the effects of the vegetation barrier. The results indicated that the ideal maturity for the vegetation barrier to achieve the most pollutant reduction is around 15-17 years and 4-6 m height. In this scenario, the vegetation barrier enhances pollutant deposition, has a moderate wake region, and generates high turbulence that promotes downwind pollutant dispersion. It is imperative to account for growth patterns when selecting vegetation as roadside barriers so that it can be maintained through pruning to achieve an ideal barrier height and optimal pollutant reduction.