Spatio-temporal Evolution Patterns And Influencing Factors Of PM_2.5 In The Yangtze River Economic Belt

Since the reform and opening up,rapid industrialization and urbanization have gradually deteriorated the quality of China's atmospheric environment,and many regions have frequently suffered from large-scale severe haze.Fine particles(PM_2.5),as the key factor that causes haze pollution,has become the primary air pollutant in most of China.As a result,it has attracted widespread attention from the government and the public.The Yangtze River Economic Belt is not only an important strategic support belt and economic engine in China,but also a leading demonstration zone for the construction of ecological civilization.Therefore,it determines the green and sustainable development policy of"jointly grasping great protection and not carrying out large-scale development".In this context,this paper reveals the temporal and spatial evolution and the characteristics of regional pollution of PM_2.5.5 pollution,and explores the driving factors and mechanism of PM_2.5.5 in the Yangtze River Economic Belt,which is of great significance for formulating scientific and reasonable air pollution prevention and control policies and promoting the high-quality development of the Yangtze River economic belt.Based on the related theories of economic geography,environmental economics,and spatial econometrics,this paper comprehensively uses Theil index,spatial correlation analysis,spatial Markov probability transfer matrices to analyze the temporal and spatial evolution pattern of PM_2.5.5 pollution in the Yangtze River Economic Belt from four aspects:time series evolution,spatial differentiation,spatial agglomeration,and spatial-temporal dynamics.In addition,this paper fully elalorates the spatial correlation of PM_2.5,and quantifies the effect degree of different natural and human factors as well as the spatial effect of these factors based on the spatial econometric model.The main research conclusions are as follows:?1?From 2000 to 2016,the PM_2.5.5 concentration in the Yangtze River Economic Belt increased showed a pattern of"W"-shaped fluctuated growth.Among them,PM_2.5.5 increased rapidly from 2000 to 2007,decreased gradually from 2007 to 2012,and showed an inverted"V"fluctuation from 2012 to 2016.Specifically speaking,the growing rate in the middle and downstream regions was higher than that in the upstream region,and the there is no change in PM_2.5.5 in terms of the basic pattern which decreases from the downstream to midstream part then to the upstream.The proportion of grid area of low concentration and lower levels of PM_2.5.5 showed a downward trend,while that of higher and high concentration showed an upward trend.?2?The overall difference of PM_2.5.5 presented an shrinking trend in 2000-2016.The difference within the region is the main factor causing the overall difference.The difference within the region presented a reducing trend,while the difference between regions presented an expanding trend.The spatial difference of PM_2.5.5 concentration in the Yangtze River Economic Belt was significant,showing a clear distribution trend of"high in the middle and lower reaches,low in the upper reaches"and"high in the north and low in the south".The spatial distribution of the PM_2.5.5 high-concentration area has an evolutionary process of"expanding first and then shrinking",and gradually gathers in the northern Jiangsu and Anhui in the periphery and the central and eastern Hubei,while the areas with low and lower concentrations have been consistently distributed in Yunnan,western Sichuan,and western Guizhou.?3?From 2000 to 2016,there was a significant spatial agglomeration characteristics between PM_2.5.5 concentrations in the Yangtze River Economic Belt,and the degree of agglomeration tends to increase.The H-H cluster area of PM_2.5presented a expanding tendency,while the L-L cluster area remains stable,and the whole shows a"diagonal"structure with northeast and southwest polarized development,and the center of gravity inclined to the northeast.?4?The evolution of PM_2.5.5 type has maintained the stability of the original state.Most of the changes in PM_2.5.5 concentration types occur in successive transfers between adjacent types,and it is difficult to achieve a leap-forward shift.The regional background plays an important role in the spatial-temporal evolution of PM_2.5concentration.The Cities with higher PM_2.5.5 concentration have positive spillover effect.If a city is adjacent to a city with a high PM_2.5.5 concentration,the probability of its PM_2.5.5 moving upward increases and the probability of moving downward decreases.while those with lower PM_2.5.5 concentration have negative spillover effect.As a result,the"club convergence"phenomenon of"high agglomeration,low concentration"has been gradually formed in the spatial pattern.?5?There is a significant spatial spillover effect of PM_2.5.5 pollution among cities in the Yangtze River economic belt.PM_2.5.5 pollution is positively correlated with annual mean relative humidity,per capita GDP,population density,urbanization level,industrialization level and energy consumption,and it is negatively correlated with annual mean wind speed,annual mean temperature,and vegetation coverage.however,annual precipitation have no significant effect on PM_2.5.5 pollution.Annual mean wind speed,vegetation coverage,population density,industrialization level and energy consumption not only directly affect local PM_2.5.5 pollution,but also affect PM_2.5pollution in neighboring cities through indirect effects.Based on the research finding,we proposed measures to reduce PM_2.5.5 pollution from the aspects of establishing regional cooperation and coordination mechanism,transforming economic development mode,optimizing industrial structure,improving energy efficiency,and promoting new urbanization.