Impact Of Exogenous Particulate Matter Pollution On Residential Neighborhoods Outdoor Environment And Its Mitigation

Recent years have witnessed rapid improvement of air quality in China,as industrial emission and raised dust have dropped massively;meanwhile,the proportion of regional or exogenous particulate matter has increased significantly,and heavy pollution weather processes under the combined effect of adverse meteorological conditions and regional pollutant emissions occur from time to time,causing serious negative impacts on residents’ health.Also,future potentials in emission reduction is growingly limited.Therefore,it is urgent to expand the paths of particulate matter pollution responses and strengthen the end-of-pipe treatment for exposed people and affected areas.The design optimization,renewal and improvement of urban residential areas can not only regulate the spatial elements that directly affect the movement and distribution of particles,but also guide and limit the scope of residents’ activities,thus reducing the spatial and temporal overlap of foreign atmospheric particles and residents.Therefore,it is an important potential pathway for spatial planning to participate in particle pollution mitigation.The existing research on optimization and improvement of residential environment often adjusts multiple indicators describing the spatial elements and background environment of residential area to build different scenes,and then inspects the status of relevant physical fields around residential area under various scenes through simulation or scale down experiments,and gives improvement suggestions accordingly.However,the complexity of the near surface wind field of the built environment and the high diversity of the spatial form of residential buildings may cause this pathway to face difficulties in engineering feasibility and practical availability: from the perspective of engineering feasibility,the common indicators describing the background particulate matter pollution process and the spatial form of residential areas constitute a high dimensional variable space,making the number of possible scenes far exceed the computational power and time resources that can be utilized;From the perspective of practical usability,the construction of hypothetical pollution processes and design schemes using simple indicators will have a large deviation from the complex reality constrained by many factors,resulting in the non-existence of a large number of simulation scenarios.In response to the above problems,this study proposes and implements a residential improvement path based on actual particulate pollution scenarios and common residential spatial patterns.Specifically: 1)Identify typical exogenous particulate pollution process patterns in a specific area.First,establish a small-scale and highfrequency monitoring network for near-surface particulate matter and meteorological conditions in the built environment,and obtain minute-level time series data of particulate matter concentration at multiple sites;then,integrate signal processing techniques such as discrete wavelet decomposition and dynamic time warping to overcome the interference of near surface complex wind fields and multi-source particulate matter,extract the background particulate matter concentration patterns,and thus characterize the asynchronous relationship between time series and the background change and the peak/cumulative concentration relationship between each site and the background change;Finally,the time series clustering method is used to identify the background particulate matter pollution process with relatively consistent relationship between stations as a representation of the movement pattern of exogenous particles near the surface.2)Identify the typical spatial pattern of residential buildings in this area.First,collect and register the building contour and floor number data of the study area and the boundary data of the residential area;Then,the mathematical morphology method is used to characterize the irregular spatial morphology commonly existing in the residential area,forming a morphological index set describing each building and each residential area;Finally,based on the above high-dimensional and sparse data sets,CLIQUE subspace clustering algorithm is used to find the common features and typical patterns of the spatial morphology of residential buildings in the study area.3)Combine the above to form typical scenes and calculate their key physical fields.Based on the typical exogenous particle pollution process and the spatial morphology of the residential area,a small number of numerical examples that can cover most of the actual scenes in the study area are formed,and simulation under turbulence model and discrete phase model is used to investigate the particle concentration distribution and physical field in the residential area under these scenes.4)With the simulation results,the improvement measures with low cost and high feasibility are proposed.According to the simulated particle concentration field and movement trajectory,for each spatial form of residential area,considering the main particle pollution process,comprehensive suggestions are given from the aspects of spatial form optimization and adjustment,road network garden planning and design,vegetation layout,parking lot site selection,etc.Taking Wuhan City as the main research area,the research found that: 1)By analyzing and extracting actual particle pollution process and residential space form,a small number of simulation experiments can directly serve a large number of actual scenarios.There are 6 typical particulate pollution processes and 5 typical residential spatial patterns in the study area;the cross-combination of 2 dominant particulate pollution processes and 10 typical residential spatial patterns or their deformation forms can sufficiently provide direct references for environmental improvement under most particulate pollution processes.2)The analysis method integrating discrete wavelet decomposition and dynamic time warping can well cope with the complex interference and dynamic asynchronous problems faced by the residential-scale near-surface particulate matter monitoring network.The time series variation of near-surface particulate matter concentration in the built environment is mainly composed of three main frequency components with feature scales of less than half an hour,1-8 hours and 1-2 days,but a sampling interval of at least 5–15minutes is required to accurately characterize its spatiotemporal processes.Integrating discrete wavelet decomposition and dynamic time warping,the response differences of stations at different locations during the previous particle concentration increase process are accurately captured.This difference shows a clear connection with the source direction and potential movement process of particulate matter.Therefore,it is an effective means to identify and characterize exogenous particulate matter pollution processes.3)The spatial morphology analysis method of residential area based on mathematical morphology and CLIQUE subspace clustering can effectively characterize urban residential areas with irregular shapes and extract their typical patterns.Empirical analysis shows that the residential areas in the study area are mainly composed of slab,irregular approximate slab and double-convex buildings,and there are a large number of oblique angles,semi-enclosed places and other multiscale and irregular spatial morphological features.Mathematical morphology algorithm can effectively extract the above features,and CLIQUE subspace clustering algorithm can realize the aggregation of high-dimensional morphological features,and finally achieve the extraction of typical patterns of residential spatial morphology.4)Utilizing the spatial heterogeneity of the particle movement trajectory and its concentration field at the pedestrian height in the residential area under the process of exogenous particulate pollution,comprehensive improvement measures that take into account the cost and practical feasibility can be achieved.Simulation results show that under the same pollution process,the difference in pedestrian height concentration between different residential morphological patterns can reach about 1 times,and the difference in concentration within residential areas can reach 3-5 times.Therefore,choosing an appropriate residential space form model or effectively guiding the residents’ circulation can significantly reduce the residents’ exposure to foreign particulate matter.It also shows that the movement of foreign particles is blocked and restricted by the building walls and surrounding airflow,and there are several relatively clear entry and exit passages in most scenes;there are also several key points for the movement of atmospheric particles in and around residential areas.Therefore,for different key passages and key sites,taking blocking or dredging measures at a certain height can actively reduce the entry of foreign particles into the residential area or prevent them from staying in the residential area.