Research On Spatial-temporal Characteristic Of PM_2.5 And Exposure Risk In Nanjing

The continuous advancement of industrialization and urbanization has accelerated economic growth,improved people’s living standard,and also caused a surge in energy consumption,making fine particulate matter(PM2.5)an important pollutant in the urban atmosphere that threatens people’s health.Urban PM2.5 pollution is gradually becoming an environmental issue that people care about.As one of the core cities of the Yangtze River Delta urban agglomeration,Nanjing has long been a city with serious PM2.5 pollution,and it has more than 8 million permanent residents,which poses a high risk of population exposure.Therefore,investigating the characteristic of the temporal and spatial changes of PM2.5 pollution in Nanjing during recent years,analyzing its impact factors,and using this as a basis to simulate the spatial distribution of PM2.5 pollution,and then assess the population exposure risk is beneficial to provide a theoretical reference for PM2.5 pollution prevention in Nanjing.Based on national air quality monitoring data,land use data,road network data,population distribution data,industrial emissions data,terrain and meteorological data,using ensemble empirical mode decomposition,mixed geographical weighted regression model,land use regression model and other methods,this study explores Spatio-temporal changes of PM2.5 pollution in Nanjing from 2014 to 2018,and clarifies the response factors at the time scale and influencing factors at the spatial scale.On the basis of the above research,the spatial distribution simulation of winter PM2.5 pollution is implemented and the risk of PM2.5 population exposure is accessed in Nanjing 2018.The main conclusions of this study are as follows:(1)Research on Spatial-temporal differentiation of PM2.5 in Nanjing shows that the PM2.5 pollution in Nanjing from 2014 to 2018 indicates an improvement trend from urgent to slow.The seasonal variation of PM2.5 pollution is shown as "high in spring and winter-low in summer and autumn";monthly change shows a U-shaped distribution,with peaks in January and December,and valleys in August and September;diurnal change is mainly characterized by "double peaks",with peaks occurring around 10am and 23pm.Meanwhile,the PM2.5 pollution in Nanjing shows characteristics of inter-day(3 days,7 days,14 days,and 27 days)and inter-month(60 days,140 days,406 days,913 days,and 1826 days)scale.PM2.5 pollution is more serious in the Olympic Center,Ruijin Road and Shanxi Road,while it is low near Xuanwu Lake and Xianlin University Town.(2)Research on influencing factors of PM2.5 in Nanjing shows that the response of PM2.5 to CO is slightly weakened with the increase of time scale,showing that low-carbon policies is also conducive to control PM2.5.Meanwhile,the response of PM2.5 to O3 appears to be significantly negative on a long-term time scale,so the formulation of PM2.5 control measures still needs to pay attention to ozone pollution.Precipitation helps to dilute PM2.5.In a short time scale,high pressure and low temperature can alleviate PM2.5 pollution,while in a long time scale,low pressure and high temperature are more conducive to PM2.5 diffusion.In 2018,the impact of construction land,population,elevation,and meteorological conditions(atmospheric pressure,precipitation,and temperature)on PM2.5 pollution in Nanjing shows spatial homogeneity,while forestland,grassland,water body,subway,state-province-county road,township road,and other roads are local variables that affect PM2.5 pollution.The impact of grassland,state-province-county road,and township road are characterized by "obvious partition",and the zone boundary is BaguazhouZhongshan Scenic Area.(3)Simulation study of spatial distribution of PM2.5 in Nanjing shows that improved geographic weighted regression(LUR)model with mixed geographical weighted regression(MGWR)model has better fit than with geographical weighted regression(GWR)model that the former R2 is 0.74 and the latter is only 0.65.Meanwhile,the average error of the test sample of the MGWR model is 11.85%,which shows high precision.The PM2.5 pollution in Nanjing in the winter of 2018 shows the characteristics of "one high-one low and multiple scattered points".The high pollution areas are located in Jianye district and its surroundings,while low pollution areas are located on the south and north shores of the Yangtze River where Baguazhou in Qixia district is located.The scattered high-value areas are mainly distributed in Pukou and Qixia district.(4)Risk study of population PM2.5 exposure in Nanjing shows that the high exposure risk in Nanjing based on PM2.5 concentration is concentrated in key scenic areas,traffic congested areas,densely populated areas,polluted gas emission companies and industrial parks,while the exposure risk is relatively low in universities and sub-key scenic areas.Therefore,it is necessary to propose control measures for different characteristics of high-exposure risk areas,such as diversion tours and traffic control for key scenic areas.Meanwhile,the exposure risk in Nanjing based on population distribution shows a concentric diffusion structure.The central urban area shows high exposure risk,and patches of sub-high risk appear in the sub-urban areas,so relevant measures need to be proposed to control "one main-core,multiple sub-cores".Adjacent Jianye district,Yuhuatai District,and Gulou district are high-risk areas based on population-weighted.The joint prevention and control of PM2.5 exposure risk in these three areas should be strengthened.At the same time,more attentions should also be paid on the densely populated areas of Qinhuai district with high PM2.5 concentration.