Study On The Spatial Morphology Of Urban Metro Entrances And Exits Based On Fine Particulate Matter Simulation

With the increase in the use of subways and the increase in research on environmental contamination related to the system,there is a growing concern about the exposure to gaseous environmental contaminants and the potential health risks of the subway system.However,due to the location of urban metros in busy areas and closed structures,there are many sources of pollution in the surrounding environment,resulting in a tendency for pollutants to accumulate indoors.Based on the demand of urban residents for a healthy built environment,it is important to improve the air quality in underground commuting spaces,to form a metro entrance and exit design that facilitates the deposition of fine particles,and to form an external space layout that facilitates the dissipation of fine particles.This study,firstly,through a review of domestic and international literature,compares the research of domestic and international scholars on the spatial morphology and air environment of urban metro entrances and exits.Secondly,research is conducted on different urban metro entrances to summarise the indicators and typical parameters of their spatial morphology classification and to establish the model corresponding to the external environment and internal design.The validity of the software simulation methods for different scales of fine particulate matter concentrations is compared with the experimental scaled-down model for the metro station and the actual measured data for Hefei Changhuai Street,and the simulation parameters are modified in comparison with the experimental results.In this way,a simulation study of fine particulate matter at typical underground entrances and exits is carried out to analyze the indoor and outdoor fine particulate matter concentration distribution at underground entrances.Finally,by analyzing the results of the simulation study,the influence of the spatial form of the metro entrance design index on indoor air quality is derived,and finally,the spatial form of the metro entrance design strategy is proposed.The main conclusions are as follows:(1)Based on literature research,satellite remote sensing and field research data,this paper firstly composes and summarizes the functional composition,flow organization and external environment of the underground entrance/exit area in hot summer and cold winter and extracts three morphological index factors from the external spatial perspective: street valley morphology,relative position and entrance form;and extracts three morphological index factors from the internal spatial perspective: opening position,entrance height/width ratio and roof morphology From the internal spatial perspective,the three morphological indicators of opening position,entrance height and width ratio and roof form were extracted and typologically analyzed.(2)The simulation of fine particulate matter at the entrances and exits of the metro under different street environments revealed that the PM2.5 concentration on the windward side of the metro entrance was,on average,87.3% higher than that on the leeward side.For the side entrances,the windward side is more polluted than the leeward side;the descending street canyon pattern is the most unfavourable for the side entrances;for the relative change of the location of the entrances along the Y-axis direction(street extension direction),the fine particulate matter concentration in the leeward side entrances shows a trend of higher concentration near the centre of the building For the relative changes in the location of the subway entrance along the Y-axis(street extension direction),the leeward underground entrance shows a trend of higher concentrations near the centre of the building.In contrast,the windward underground entrance always maintains a trend of lower concentrations in the middle and higher concentrations on both sides.(3)The predicted mean particulate matter concentrations at the internal platform level for the three types of underground entrances were ranked as follows: windward side > underground island entrance > elevated type > leeward side;the concentrations of fine particulate matter in the buildings on both sides of the street canyon containing the underground entrance decreased as the building height increased.(4)Simulation of the building design of underground entrances reveals that: by studying the interception efficiency of particulate matter under different wind velocities at the front and side entrances,the interception rate of particles at the side entrances is 2-3 times higher than that at the front entrances;when the entrance height to width ratio is less than 1:1,the larger the entrance width is,the better the overall air quality of the underground station;the design of the roof form of the underground entrance has the most favourable indoor particulate matter The sloping roof is the most favourable to the reduction of indoor particulate matter,followed by the flat roof and the worst without a roof.When the outdoor airflow is 1m/s,the roofless form’s interception rate of particulate matter is only 0.019.(5)The spatial design can improve the entry of particulate matter inside the station,but the interception rate of particulate matter through the spatial form of the metro entrance building is at most 10%.In contrast,the external spatial design has a greater impact on the concentration of particulate matter inside the metro.For neighbourhoods with more serious road pollution,good layout locations should first be considered at the early stage of metro design,and other spatial designs should be used to create convection and return flows to reduce the direct infiltration of outdoor pollutants.This study aims to provide a technical basis for the planning and renewal of the urban metro and the design and renovation stages of the building and to explore methods of designing urban metro entrances that are conducive to energy saving and emission reduction,promoting healthy behaviour and improving air quality,from a "meso(building layout)-micro(building design)" scale.By adjusting the layout of the external space of the metro and changing the parameters of the building design,the concept and principles of ecological civilization are fully integrated into the planning and design process of urban metro development so that the environment of metro use can reach a healthy state and the underground transport space can become a place of high quality and suitable for human habitation.