Effects Of Vertical Green On PM_2.5 In Street Canyon

In recent years the problem of air quality pollution caused by PM_2.5 raises widespread attention to the community,becoming a major environmental problem.Vertical green has a better capturing particles effect,and is expected to be an effective way to improve air quality to combat particulate matter.Therefore,there is a need to discuss vertical green capture ability and its influence to particulates’s diffusion pattern.This article chooses the street canyon as study object which is a typical city-size environment.The main works of the research about effects of vertical green on PM_2.5 in the streets canyons are as follows.Firstly,give a summary of the distribution characteristics of particles and the influencing factors in street canyons,and get well known of related researchs of vertical green types and its purification of air.Secondly,measuring experiment of particle matter concentration in Wuhan streets is done,and the accuracy of simulations is tested by comparing experiment data with simulation calculations.Thirdly,introduce microclimate software ENVI-met main features and mathematical models.The parameters for vertical green leaf area density（LAD）and the emission rate of pollution are set.And then,ENVI-met simulation is used to analysis vertical greening impacts of particle matter from two aspects,such as PM_2.5 total deposed mass and PM_2.5.5 concentration change.The parameters involved including width-to-height ratio of street canyon,relatively building height and wind directions.Finally,in order to exam the result feasibility conclusions are applied to the street which has been measured.The main conclusions are as follows.（1）Vertical green have two influences on particulates,which is removing particulate matter and affecting dispersion of particulate matter.They reflect to PM_2.5deposed total mass and particle concentration change.Vertical green can be effective for particle sedimentation,but it also reduces wind speed and increase particle concentration.So we should combine two values when evaluating vertical green.（2）Vertical green deposed mass varies in different types of street canyons and different wind directions.The smaller width-to-height is,the more particle will be deposed;in descending type street canyon or with 0°wind direction,vertical green will depose large amount of particle matter.（3）Vertical green impact on PM_2.5 concentrations depending on conditions in different types of streets and different wind directions.Building surface without a’wall funtion’or a low-intensity is suitable for vertical green,and PM_2.5.5 concentration in the area of the pedestrian area is lowered.But adding vertical green to the surface with high intensity wall function will due to raise of particle concentration.So building’s surface horizontal flow field is the main reference factor to determine whether vertical greening is suitable.