Research On The Influence Of Wind Environment And Urban Vegetation On PM_2.5 Concentration In Shaoshan City

Urban air environment is closely related to the health of residents,and vegetation is an important factor to alleviate air pollution.In order to understand the role of vegetation in the removal of PM_2.5,this paper studies the law of PM_2.5 spatial distribution under the impact of vegetation through theoretical analysis and computer simulation.First,this paper simulates the flow field of Shaoshan City based on the real terrain.By comparing the differences of wind field between with and without vegetation impact,It can be seen that trees can lower the wind speed and increase the turbulence intensity of flow field.The effect of trees on wind speed varies with altitude,with the greatest impact appears at the bottom of canopy layer?wind speed is reduced by 76%?.The wind speed is decreased at the peak and the original peak of velocity shifted upwards because of the effect of forest,increasing air extrusion and therefore slightly raising the velocity of air above the peak.At the same time,the turbulence intensity of leeward surface is apparently enhanced by the influence of forest and large scale vortices are formed,which increase the disturbance to the downstream flow field.Secondly,based on the flow field of Shaoshan,this paper analyzes the urban PM_2.5spatial distribution under the influence of vegetation.Though the simulation of three different pollution source conditions inside the building group,outside flow and comprehensive pollution,a conclusion can be drawn that the existence of vegetation can reduce the concentration of PM_2.5.The deposition of internal forest is related to the area of forest and the selected location.The larger the area,the greater the sediment effect.The deposition flux within the forest is greater than that at the edge and the sediment flux in the valley is greater than that at the peak.The maximum PM_2.5deposition appears at the bottom of the canopy,which can reach 97%.Forest in the upstream area can alleviate PM_2.5 pollution in the downstream area.Finally,this paper discusses the relationship between greening rate and urban PM_2.5 mass concentration and comes up with an Environmental Information Association Model.Based on this,the role of vegetation in the relationship between PM_2.5 and meteorological factors and regional pollution is analyzed.By analyzing the numerical values of impulse response,it can be seen that the highest correlation with greening rate was the response of PM_2.5 mass concentration to the impulse of relative humidity?R²=0.71?,followed by wind speed?R²=0.54?.The response of temperature shown little correlation with greening rate.The response of PM_2.5 mass concentration to the impulse of wind speed was the fastest one in all meteorological factors.the higher the greening rate,the more severe the PM_2.5 responds to the three meteorological elements and the more likely it is to fluctuate.The total response of PM_2.5 mass concentration to the impulses of all meteorological factors shown an apparent correlation with greening rate?R²=0.62?.Areas have high vegetation coverage are less susceptible to PM_2.5 pollutants from other areas.This study can provide a certain reference value for the future urban wind farm simulation and urban PM_2.5 concentration field simulation,and provide guidance for the future layout of medium-sized cities and urban green space planning.