Numerical Simulation Of The Influence Of Different Greening Models On Pollutant Diffusion In Typical Urban Street Valleys

The urban street valley is one of the important manifestations of the urban environment,and the dust caused by motor vehicle exhaust emissions and driving in the street valley seriously affects the air quality of the sidewalk space.Relevant research shows that plant greening has a good ability to reduce pollutants.However,due to the relatively closed environment of the street valley,different street valley spatial patterns and street greening patterns will have different effects on the distribution of pollutants in the street valley.Therefore,it is necessary to combine the spatial environment of urban streets and valleys to analyze the effects of different plant greening modes on the diffusion of pollution in the streets and valleys.First of all,through literature compilation,the mechanism and factors of plant greening model on pollutant diffusion are summarized and proposed.Secondly,the theoretical basis and applicability of the numerical simulation software envi-met were verified,and it was proved that the concentration field calculation model adopted by the software was applicable to the study of the interaction between plants and pollutants in the urban street valley environment.Finally,taking urban branch roads as the research object,through on-site investigation and relevant normative guidelines,the urban street valley model with typical spatial characteristics and different greening models were established.From the spatial layout of greening and individual characteristics(Leaf area density,Leaf type,plant spacing,and hedge height)explore the relationship between plant greening and the distribution of sidewalk pollutants in order to propose greening strategies to improve air quality.The research results show that:(1)Under quiet wind conditions(0.3m/s),the pollution degree of the sidewalk space in the street valley is from light to heavy in order of upper ladder street valley <shallow street valley <lower ladder street valley <ideal street valley,In the breeze condition(3m/s),the pollution degree is upper ladder street valley <lower ladder street valley <ideal street valley <shallow street valley.(2)The addition of plant greening has not improved the air quality of the sidewalk space in the street valley,but has further aggravated the pollution degree of the street valley.(3)The sidewalk space pollution in symmetrical street valleys(shallow Street Valley,Ideal Street Valley)is relatively more serious than that of asymmetrical street valleys(upper ladder street valley and lower ladder street valley),but the impact of plants on air quality in asymmetrical street valleys is greater than that of symmetric street valleys.(4)The reduction of the leaf area density of the sidewalk and the increase of plant spacing can effectively reduce the pollution concentration of the sidewalk,and the effect of leaf type and shrub height is relatively small,but the selection of larger leaf type plants and the increase of shrub height is not conducive to the improvement of pollution.