Spatiotemporal Characteristics And Drivers Of PM_2.5 Pollution In The Yangtze River Economic Belt

Since the reform and opening up,with the rapid growth of China’s economy,the rapid advancement of urbanization and industrialization,and the rising consumption of energy and resources,the haze caused by fine particulate matter(PM_2.5)has nearly reached the epidemic level and is characterized by complex,cumulative and cross-regional pollution.As a major strategy for China’s overall development in the new era,the Yangtze River Economic Belt（YREB）plays an irreplaceable role in China’s economic growth.However,for a long time,the energy-intensive economic growth mode and the non-ecological urbanization mode have made the resources and environment constraints in the YREB increasingly tight,which has brought heavy pressure to the green development of the YREB.The YREB is an ecologically fragile area in China and a key area for pollution prevention and control.The guiding principle of promoting ecological civilization construction in the YREB is to jointly promote great protection and avoid over development.The demand for high-quality development in the new period will surely lead to new breakthroughs in the governance mode,and the prevention and control of ecological environmental pollution in the YREB will also enter a new stage.Therefore,the prevention and control of smog in the YREB is not only a strong support to win the battle to protect the blue sky,but an inevitable requirement to achieve high-quality development under the new normal.In this context,it is of great significance to accurately clarify the spatiotemporal deductive law of PM_2.5pollution in the YREB and explore the driving factors of PM_2.5and its action mechanism for improving the air environmental quality of cities in the YREB and promoting the level of green development.This paper revealed the spatiotemporal characteristics of PM_2.5pollution in the YREB from the five aspects of temporal evolution,spatiotemporal differentiation,spatial agglomeration,spatial correlation and space-time dynamic by using kernel density estimation,spatial autocorrelation analysis,LISA time paths,space-time transition,and gravity model.And we further used a variety of spatial econometric models to identify and quantify the spatial effects of specific natural factors and human factors on PM_2.5pollution.The main research conclusions were as follows:（1）From 2000 to 2018,the PM_2.5level in the YREB posed an inverted U-shaped trend,which increased and then decreased.The annual variation trend of provincial PM_2.5level was quite different.The variation trend of PM_2.5concentration in Shanghai,Jiangsu,Anhui and other provinces was relatively fluctuating,while the variation trend of PM_2.5level in Yunnan,Sichuan and Zhejiang was relatively stable.The urban PM_2.5quality showed obvious characteristics of low in summer and high in winter,seasonal variation in spring and autumn,monthly U-shaped variation and daily pulse variation.The proportion of high value areas of PM_2.5grid showed an increasing trend,while the proportion of low value areas showed a decreasing trend.The overall situation of PM_2.5pollution in the YREB was still grim.（2）The PM_2.5level in the YREB showed a diagonal spatial distribution pattern,which was higher in the middle-lower reaches of the Yangtze than that upper reaches,and higher in the north bank of the Yangtze than that south bank,with obvious directivity in the lowland plain.Three PM_2.5pollution centers were generally formed in the YREB during the study period,namely Chengdu-Chongqing area,the middle reaches of the Yangtze and the northern Jiangsu and Anhui areas.PM_2.5pollution in the YREB had obvious seasonal spatial differentiation characteristics,among which,the spatial distribution of PM_2.5pollution was basically the same in spring and autumn.The PM_2.5pollution range was relatively small in summer and the air quality was good,while the PM_2.5pollution range was relatively large in winter.The northern part of the middle and lower Yangtze plain had been hardest hit by PM_2.5pollution.（3）PM_2.5pollution in the YREB had a significant positive spatial correlation.Among them,the high-high agglomeration mainly distributed in Chengdu-Chongqing and the areas of Hubei,Anhui and Jiangsu,while the low-low agglomeration stably distributed in regions of western Sichuan,Yunnan and Guizhou,posing a significant spatial convergence characteristics.The seasonal spatial pattern of PM_2.5showed significant spatiotemporal variability,and the spatial agglomeration degree increased with the transformation from spring to summer to autumn to winter.The monthly spatial autocorrelation showed periodic fluctuations,and the spatial concentration of PM_2.5in January and December was strong,while that in April and August was weak.（4）The spatial autocorrelation of PM_2.5in the YREB decreased with the increase of geographical distance,and the spatial spillover effect gradually weakened.The spatial autocorrelation scale of PM_2.5between cities was about 870km,within which PM_2.5concentration was positively correlated and the spatial concentration was more obvious.There was a certain degree of interaction between atmospheric PM_2.5and other air pollutants.Except for O₃,PM_2.5,PM₁₀,SO₂,CO and NO₂were all positively correlated with each other.（5）The overall spatial pattern of PM_2.5pollution in the YREB was relatively stable,and the growth of PM_2.5pollution in the urban area showed a strong spatial dependence.The spatial pattern evolution of PM_2.5pollution in the city had a strong spatial integration,and the coordinated high growth was moving to the middle and lower reaches of the city,while the coordinated low growth was moving upstream.The four types of spatial patterns of local correlation of PM_2.5pollution in the urban area all showed inter-modal transitions,and their spatial agglomeration had relatively high path-dependent or lock-in characteristics,and the changes among different types showed certain transition inertia.The center of gravity of PM_2.5concentration in the YREB was located at the junction of Qianjiang,Jingzhou and Xiantao cities in Hubei province,and the pattern of the center of gravity changed significantly.（6）The endogenous interaction of PM_2.5pollution in cities along the YREB was significant.Each 1%increase in PM_2.5level in the neighborhood will lead to at least a0.4%increase in the local PM_2.5level.PM_2.5levels were directly or indirectly affected by natural and human factors.The intensity of direct effect on local PM_2.5pollution was:annual atmospheric pressure>per capita GDP>annual precipitation>energy consumption>population density>vegetation coverage>relative humidity>annual wind speed>industrial structure.The order of spatial spillover effect on PM_2.5pollution of neighborhood units was:Annual atmospheric pressure>energy consumption>annual wind speed>population density>vegetation coverage.There was no significant spatial spillover effect on annual precipitation,annual temperature,relative humidity,per capita GDP,proportion of secondary industry and urbanization level.In addition,all kinds of indicators had positive and negative effects,and the degree of effect had significant spatiotemporal differences.