Study On The Influence Of Different Planting Types On PM_2.5 Concentration In Urban Road Green Belt

Road green belts play an important role in improving air quality and ensuring pedestrian safety in roads.This study took Wusu Street in Lin’an District,Hangzhou as the object of study,and studied the temporal change law of road PM_2.5 concentration through actual measurement,and verified the applicability of the software by constructing an actual site model through the software ENVI-met with the relevant data of actual measurement for simulation.Then,ENVI-met was used to carry out relevant numerical simulation to simulate the variation of PM_2.5concentration and the subtracting effect of plants on PM_2.5concentration under three planting types of"trees-herbs","shrubs-herbs"and"trees-shrubs-herbs"in four seasons.The conclusions are as follows.（1）The daily change of PM_2.5 concentration in Wusu Street was high in the morning and low in the afternoon,and the concentration of PM_2.5rose or stayed stable in the evening depending on the season.The overall air quality on the road was poor,and the average PM_2.5concentration at the roadside and sidewalk was the highest in December,the second highest in January and the lowest in July,and the PM_2.5concentration at the sidewalk only reached the national standard in June and August.The PM_2.5concentrations at the curbside and sidewalks of Wusu Street were all in the following order:the seasonal average concentrations were ranked as winter>fall>spring>summer from largest to smallest.（2）The corresponding PM_2.5 concentration values were obtained through on-site modeling and simulation,and then correlation analysis with the measured PM_2.5concentration values showed that there was a significant positive correlation between the two,and the calculated RMSE and MAPE values were 6.08μg·m^-3and 8.86%,respectively,which indicated that the small error of the simulated data was consistent with the small error of the ENVI-met software.The high accuracy also showed that the software was able to simulate PM_2.5diffusion and was applicable to this study.（3）Numerical simulations using ENVI-met showed that the overall distribution of PM_2.5in the road decreased vertically with the increase in height and spread with the wind direction,and there was an increasing trend of particle accumulation in the motorway;horizontally,among the three types of planting,except for autumn,the plant reduction rate of the"shrubs-herbs"type was the highest and most stable.In the horizontal direction,the highest and most stable abatement rate was found in the"trees-shrubs-herbs"type of planting,except in autumn,and the highest and most stable abatement rate was found in the"trees-herbs"type of planting in spring,summer and winter,while the lowest and unstable abatement rate was found in the"trees-herbs"type of planting throughout the year.This indicated that multi-layered planting structures had a higher abatement capacity than single planting structures.The abatement rate of each planting type in different seasons showed a trend of summer>spring>autumn>winter,indicating that the abatement rate of plants varied according to the season.This study monitors the PM_2.5 concentration of Wusu Street and simulates the changes of PM_2.5concentration under different planting types in four seasons,and investigates the mechanism of influencing PM_2.5 concentration in road green belts.