| In the urban environment,with the increasing number of road vehicles,the particulate matter emitted by the exhaust of motor vehicles has become one of the sources of urban air pollution,which will cause harm to the human respiratory system,especially fine particles,and ultra-fine particles are a great threat to human health.Urban road greening isolation belt,as an infrastructure of urban construction,has a certain degree of influence on the distribution of pollutant concentration in the street micro-environment.However,the current research on the impact of green belt on pollutants is more concentrated in the ideal street canyon,The diffusion distribution of gaseous pollutants lacks a comprehensive study of the distribution of particulate matter in wide streets.Therefore,it is important to understand the influence of green belts on the diffusion and distribution of particulate matter in wide streets.It can have a deep understanding of the environmental impact of urban road green belts and provide an environmental impact on the rational layout of green belts.Firstly,through the on-site monitoring of the concentration of fine particles in green areas and non-green areas,the concentration of particles in the particle size range of 0.25-32?m,the total concentration of ultrafine particles with particle size ranging from 20 nm to 1?m and meteorological parameters.The impact of green belts on changes in particulate matter concentration.Secondly,the correlation analysis between the meteorological factors and the particle size distribution of the particle size is carried out,and a multivariate regression model is established to determine the significant influence factors and contribution rates of the particle concentration.Finally,the numerical simulation method is used to analyze the influence of different green belts and green belts on the distribution of fine particles under different building layouts.The measured results show that when the average wind speed is less than 3m/s,the green belt will have different degrees of particle size.The compact green belt may accumulate a certain amount of particulate matter concentration in the sub-size segment.The effect of the permeable green belt is to reduce the particle size of 0.25?0.35?m and more than 2.50?m.Correlation analysis showed that the concentration of particulate matter in PM2.5 and sub-size segments was positively correlated with humidity and wind speed,and there was a significant correlation between meteorological factors.The results of multiple regression analysis showed that the main variables that had a significant impact on the concentration of particulate matter in the compact green belt were humidity,temperature and wind speed.In the dredging greening,the significant influence variables were a sampling position,wind direction,wind speed,and temperature.The interpretation ratio of the model can reach more than 50%,and it is significant and statistically significant.The simulation results show that the porosity of the green belt and the height of the canopy layer will have an effect on the concentration of PM2.5.When the porosity of the canopy layer is 0.7,the concentration of fine particles on the leeward side of the building will be higher than that at 0.9;the concentration value of the canopy layer height of 6m is the largest.When the green belt is placed under three different building layouts,the PM2.5 concentration level is the highest when the buildings on both sides are of equal height,followed by the decreasing,the increasing.And the side of the building,basically larger than its windward side,as the height of the building increases,the concentration will eventually become smaller.For the concentration level of fine particles at the pedestrian's breathing height within the width of the road,the concentration values in the contours of the high-rise buildings are high,while the effects of the green belt porosity and the height of the canopy layer are not significantly different,and the concentration change trend is gentle. |
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