Role of roadside vegetation as a passive method for the reduction of urban water-insoluble fine particle and impacts brought by different planting patterns

Airborne particles have been regarded as a great threat to residents’ health, especially to those living in the urban area. As a passive method for fine particle reduction, the high capacity of vegetation has been widely explored. However, a limited number of researches have reported the capturing capacity of roadside plants for fine particles lower than 2.5 μm. In this study, ten common broad-leaved plants cultivated in central China were selected to evaluate their capturing capacity for water-insoluble particles lower than 2.5 μm and to explore the impacts of different planting patterns including height, location in the street, and the distance to the street curb on their deposition load. Besides, the impacts brought by different traffic pressures were discussed as well. Interspecies difference was found among the plants facing to the same direction. Ligustrum lucidum showed the highest capacity for particles over 0.45 μm. For particles between 0.22 and 0.45 μm, Xanthoceras sorbifolium showed the highest efficiency. The change of leaf orientation has impact on the capturing capacity of tested plants for fine particles larger than 0.45 μm, while for particles between 0.22 and 0.45 μm, each tested species showed a high capacity regardless of leaf orientation. In consideration of planting patterns, with the rise of height, and the distance to the street curb, the plants’ capturing capacity for different-sized fine particles all declined. In addition, vegetation locating in the middle of the street had significantly higher capacity than those alongside the street. At last, roadside plants from urban-street showed significantly higher capacity than those from Uni-campus and City-park. Positive correlation was found between the capturing capacity and the traffic pressure regardless of taking all plant species as a whole or comparing them respectively. This study expands the cognition of roadside plants as an effective passive filter for water-insoluble fine particle smaller than 2.5 μm and provides insights for further roadside green infrastructure planning to improve urban air quality.