The regulation effect of urban green space on air particulate matter concentration under different matrices in Xi'an city

Urban green space can effectively alleviate air pollution, in which vegetation structure plays an important role. However, these green spaces with varying vegetation structures exist in different environmental backgrounds of the city. By analyzing the influence of the different environmental backgrounds on the dust retention effect of green spaces with varying vegetation structures, green spaces can be truly utilized as a solution in alleviating air pollution. Therefore, according to the typical characteristics of landscape patterns and different coverage ratios of green areas in Xi'an city, China, the matrices of urban landscape were divided into three types, which include "green space", "grey-green mixed space" and "gray space." In each environmental background, urban green space was divided into three levels: horizontal structure, species composition and vertical structure. Subsequently, 13 types of green spaces with different vegetation structures and three hard (no vegetation present) squares as control groups were selected. A one-year on-site monitoring was conducted on urban green spaces and concentrations of TSP, PM10, PM2.5 and PM1. The results showed that: (1) In the green space, the concentrations of PM1 and PM2.5 were relatively higher. In the grey-green mixed space, the average concentration of air particle of all four particle sizes was the lowest. In the gray space, the concentrations of PM10 and TSP were more concentrated. (2) Under the same matrices, due to the different locations of the plots, the concentration of air particles of different sizes was significantly different. Under the different urban environmental backgrounds, temperature, relative humidity, wind speed and air pressure all showed the same trend in the change of air particle concentration. (3) The one-layer green space structure was most suitable for planting. Considering the green space, the coniferous one-layered green space (CO) structure was recommended. The partly-closed broad-leaved one-layered green space (P-CBO) was found to be more suitable for the grey-green mixed space. Considering the gray space in the city center, it was suggested to plant the closed mixed coniferous and broad-leaved one-layered green space (CMO) structure. The findings provide empirical support for the future collocation of urban green vegetation structure and the improvement of urban air quality.