The Spatiotemporal Effect And Driving Mechanism Of Urbanization On Air Pollution In The Yangtze River Delta Region

China has experienced an unprecedented rapid urbanization process,which has not only promoted economic and social development,but also brought environmental problems such as air pollution,especially in developed urban agglomeration areas.As the atmospheric environment is a typical "regional public goods",the change process of air pollution among cities shows obvious synchronization.As the level of urbanization increases,the region is moving towards integrated development,and the flow of urbanization factors changes from urban scale to urban agglomeration scale,making the regional atmospheric environment change complex and dynamic.In order to analyze the impact mechanism of urbanization on air pollution in the process of urban cluster moving towards integration,this paper takes the 41 prefectural cities in the Yangtze River Delta region as the research object.This paper constructs the comprehensive index of air pollution and the evaluation system of comprehensive urbanization firstly,and carries out exploratory spatial data analysis on urbanization and air pollution in order to clarify the spatiotemporal evolution characteristics and spatial correlation mode of the two;by using panel data model and spatial panel econometric model,this paper clarifies the impact mechanism of urbanization on air pollution,investigates the reliability of the model from the endogenous and heterogeneous dimensions,and further discusses the applicability of Environment Kuznets Curve(EKC)theory and spatial EKC theory;then constructs the model of interaction effects between factor mobility and urbanization,revealing the driving mechanism of urbanization on air pollution in the Yangtze River Delta region,and puts forward some targeted policy implications for the development of regional high-quality integration.Based on the above analysis steps,the main conclusions obtained in this paper are as follows:(1)Based on the results of exploratory spatial analysis,the comprehensive air pollution index in the Yangtze River Delta shows a dynamic feature of first increasing and then decreasing,and the comprehensive urbanization level maintains an upward trend.The comprehensive air pollution index in developed cities along the Yangtze River is relatively high,while the pollution level in southwestern Zhejiang is relatively low;the comprehensive urbanization of cities in the Yangtze River Delta is basically a core-periphery structure in the space.The spatial agglomeration characteristics of the comprehensive urbanization and the comprehensive air pollution index are significant,and neighborhood urbanization may have spillover effects on air pollution.The number of negatively correlated areas(H-L type,L-H type)between the comprehensive air pollution index and comprehensive urbanization is increasing in the bivariate LISA diagram,indicating that the increase in the level of urbanization in the neighborhood may reduce local air pollution.(2)Based on the results of confirmatory data analysis,comprehensive urbanization and its sub-dimensions all contribute to air pollution from the estimation results of mixed OLS model,while the fixed effects model can provide more accurate estimation results based on the F test and Hausman test.The individual fixed effects model shows that comprehensive urbanization has a negative impact on air pollution,and the impacts on air pollution among urbanization sub-dimensions are also different.Land,economic and social urbanization sub-dimensions can all significantly reduce air pollution,while population urbanization exacerbates air pollution.Considering the large differences between the results of the mixed OLS model and the fixed effects model,by examining its multi-dimensional heterogeneity in time,space,and level,it is found that the impacts of urbanization on air pollution are different in different periods,regions and grades,indicating that mixed OLS estimates are not consistent.Among other socio-economic factors,population size,degree of openness,and energy efficiency have positive effects on air pollution,while technological progress and industrial structure variables have negative effects on air pollution;natural factors such as temperature and precipitation show non-significant effects.(3)The results of EKC test show that with the increase of urbanization,the comprehensive air pollution index shows an inverted N-shaped change trend of "decrease-increase-decrease".There are two turning points in the development of urbanization in the Yangtze River Delta.The first turning point is the critical point of economies of scale.When urbanization crosses this turning point and enters a period of rapid development,pollution emissions cannot be effectively controlled,and urbanization will aggravate air pollution;the second turning point is the point of improvement in technical effects.Due to environmental regulations and clean technology research and development,the impact of urbanization on the air environment is gradually improving.When considering the spatial effects,urbanization has a negative spillover to air pollution,which makes the critical point of the economic effect of scale lagging and the point of improvement of the technical effect advancing.Detecting the driving mechanism of urbanization on air pollution under the condition of factor mobility,it is found that the flow of factors such as population,capital and industry will affect the development of regional urbanization and then affect the air environment.There is spatial heterogeneity in the impact of regional population economic connections on urbanization.On the one hand,it can promote the development of urbanization in developed cities,and on the other hand,it can also inhibit the urbanization process of backward cities;the industrial division transfer in the Yangtze River Delta region promotes the development of industrial urbanization and aggravates the regional air pollution,supporting the existence of the Pollution Paradise Hypothesis(PPH)in the Yangtze River Delta.The backward cities provide the undertaking place for the industrial transfer in the developed regions,and the dominant one is the transfer of polluting enterprises from the developed cities to the backward cities.The unified market management brings great opportunities for the urbanization development of the leading cities,but the rapid development of urbanization will also lead to the damage of the air environment.Based on the discussion of the relationship between urbanization and air pollution,the policy implications of regional high-quality integration are proposed.The main points are as follows: Taking into account the advancement of urbanization differentiation,we should thoroughly implement the new urbanization strategy to ensure the high-quality development of the ecological environment.Cities that have not passed the first turning point need to speed up the upgrading of industrial structure and strictly control the entry threshold of pollution-intensive enterprises;cities that are in the antagonistic zone should actively introduce cleaner production technologies,cooperate with environmental regulations and policies,and quickly enter the win-win range of urbanization development and environmental protection.We should pay attention to the joint prevention and control of regional air pollution,and establish a reasonable ecological compensation mechanism.The population flow in backward areas is passive,while exporting labor resources to developed areas,we must also pay attention to the introduction of high-quality talents to stimulate local development potential;and we should rationally guide industry and capital transfer,prevent the risk of influx of polluting enterprises,and grasp the opportunities of the promotion of local industrial chain to achieve regional high-quality integrated development.