Optimization Of Spatial Form Of High-Density Urban Street Canyon Based On Air Quality Improvement

Under the guidance of the"people-oriented"development concept and the"stock and quality"development model,the urban built environment has entered a new phase,and remarkable progress has been achieved in the treatment of air pollution through refined management of key urban areas,key regions and key locations.However,urban air quality is still generally"weather-affected",with 29.8%of cities still experiencing above-average PM_2.5concentrations.Urban street canyons are an important urban spatial pattern for residents to participate in social life,and the air quality in street canyons can affect the health,comfort and livability of residents.In response to the demand of urban residents for a healthy built environment and in response to popular environmental events of concern to government departments,a study of PM_2.5real-world measurements and simulated street canyon spatial patterns based on air quality improvement was conducted to optimise the urban environment.This study selects Tong’an Street in Baohe District,Hefei City,Anhui Province as the study area,and carries out a systematic analysis of the spatial and temporal variation characteristics of fine particulates in the street canyon in the different seasons.The design and the optimisation of the spatial form of the street canyon are proposed from a meso perspective,and the optimisation strategy of the volume and form ratio is proposed for the special building form of the commercial sunken plaza from a micro perspective.It is concluded that the overall pollution situation in Hefei is good,mainly excellent;the number of polluted days distribution In general,it demonstrates greater prevalence during winter and spring and decreased occurrence in summer and autumn.This phenomenon is caused by the fact that in spring and winter temperatures are low and temperatures near the ground are lower,but temperatures above the ground are higher than near the ground due to a smaller drop in temperature,making it easier for inversions to occur.Using Tongan Street Canyon as the research object for the actual measurement study,and using AQI to evaluate the Maanshan Road Street Canyon in Tongan Street,the results show that its air quality is mainly excellent,with air quality levels mostly distributed in Class I and Class II;PM_2.5quality intensity is ranked from highest to lowest:B（in the commercial sunken square）>D（next to the buildings adjacent to the road）>C（next to the surface car park）>A(（in urban setback plazas）>E（at the entrance to pocket parks）.The street canyon design indicators and climate indicators were quantified from a multi-dimensional perspective.The results show that surface vegetation cover,building height ratio,street aspect ratio and relative elevation play a key role in the variation of PM_2.5,with surface vegetation cover and building height ratio contributing 88.3%to the variation of PM_2.5.By combining the key design indexes of the street canyon spatial pattern derived from the actual measurement with the optimisation simulation,it is found that by increasing the surface vegetation cover in the street canyon,the fine particulate matter mass concentration is reduced by 5.7%year-on-year;by lowering the altitude of the structures located on the side of the street canyon facing the wind,the fine particulate matter mass concentration is reduced by 3.3%year-on-year;by changing the width of the road in the street canyon and increasing the spacing of the buildings on both sides of the street canyon,the fine particulate matter mass concentration is reduced by by 24.3%.The aforementioned three optimization strategies are all beneficial for creating outdoor interactive spaces in urban streets and improving the living environment for urban residents.The study concludes with optimisation recommendations for the air-poor sunken plaza spaces in urban street canyons;by（1）widening the volume to alleviate the accumulation of pollutants;（2）rationalising the layout to improve the surrounding environment;（3）controlling the plan and choosing a reasonable form;and（4）increasing greenery to create grey-green spaces;further improving the air quality of the sunken plaza.From the perspective of the constructed environment,this investigation centers on the subsequent two elements:the correlation between various indicators of street canyons and fine particulates in the spatial governance of street scale;and the layout changes of special architectural spaces and surrounding environmental elements in the spatial scale of buildings.It is intended to offer a planning strategy and scientific basis for pollution mitigation in urban street canyons,and to provide a reference for the spatial form of new and modified urban street canyons and the development of sustainable urban transportation and travel policies.Figure[37]table[17]reference[84]...