Research On Reduction Efficiency Of Roadsine Greenabelt Width On Air Pollutabts

City road green belt which is an important part of urban greening construction, playing an important role in the improvement of the urban environment. The efficiency of road green belt reducing air pollutants is closely related to the green belt vertical structure and width. The width of the green belt is an significant indicator of designing, and reasonable green belt width should be determined by urban road traffic condition, road layout, pollution sources, plant species, plant configuration and climatic characteristics. In this paper, we selected three levels of city roadrthe main trunks,secondary roads and branch in Wuhan Qing shan district, to measure the atmosphere mass concentration of TSP, PM10, PM5, PM2.5, SO2, NO2in different grade road green belt widths (5m、10m、15m、20m) respectively. On the basis of those, we contrasted and analyzed the air pollutant reduction percentage of green belt under the different widths, determined the best green belt width range to reduce the air pollutant, in order to provide the basis for urban road green belt planning and design. The main results are shown as follows:(1) The mass concentration of atmospheric particulate matter in different levels of road have a significant difference:main trunk> secondary road>branch. The mass concentration of NO2in gaseous pollutants of difference levels of road are different, and it has the same performance:main trunk (C=250μg/m3)> secondary road (C=246μg/m3)>branch (C=155μg/m3), while the SO2mass concentration has no significant difference. The traffic in different levels of road are significantly associated with atmospheric particulate matter and the mass concentration of NO2(P主=0.821、P次=0.87、 P支=0.839), while not the mass concentration of SO2(P主=0.534、P次=0.269、P支=0.406).(2) In main road green belt from the roadside5m,10m,15m,20m,the percentage reduction of PM2.5and PM5don’t vary significantly, and the reduction percentage of TSP and PM10in10m,15m,20m also has no significant difference. The percentage reduction of SO2in the10m reaches its maximum value, then reduces gradually. While the percentage reduction of NO2don’t show obvious rule. The reduction percentage of PM2.5、PM5and PM10in secondary roads greenbelt stabilized at5m. The reduction percentage of TSP at10m,15m,20m green belts were not significantly different. TSP in branch green belt were no significant difference at10m,15m and20m. The reduction percentage of PM2.5、PM5and PM10at5m,10m,15m,20m don’t show significant difference. The reduction efficiency of gaseous pollutants in secondary roads and branch were not significantly different.(3) Different green belt width of the main trunks, secondary roads and branches has no significant effect on the reduction efficiency of small particle size (PM5, PM2.5), while has significant influence on PM10and TSP reduction efficiency, and the percentage reduction at5m,10m of different levels road increased gradually, stabling at15m,20m. Therefore, in order to improve the reduction efficiency of atmospheric particulate pollutants significantly, urban road green belt width should not be less than10m. The mass concentration of SO2and NO2in different width of the green belt at5m reduce significantly, and lower than the control value (0m). the reduction percentage of SO2and NO2in different widths green belt do not change significantly. The best green belt width to reduce gaseous pollutants efficiently was less than5m.(4) The analysis of air pollutant reduction efficiency in different levels of road green belt shows that there is a significant negative correlation between the wind speed, relative humidity and the air pollutant reduction percentage at the green belt width. And wind has influence on TSP reduction efficiency of5m (PTSP-5m=-0.943), NO2reduction efficiency of5m,10m (PN02-5m=-0.943, PN02-10m=-0.812), as well as SO2of20m (PSO2-20m=-0.899). While relative humidity affect the reduction of the small particulate PM2.5and PM5significantly (P PM2.5-5m=-0.986, P PM2.5-10m=-0.812, P PM2.5-15m=-0.829, P PM2.5-20m=-0.943, PPM5-10m=-0.812). Temperature, noise and traffic volume have no significant influence on the air pollutant reduction of the green belt.