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Spatiotemporal Characteristics of the Pollution Reduction Effect of Differentiated Coordinated Development in the Yangtze River Economic Belt, China

4 The pollution reduction effect of regional development could be analyzed more comprehensively from the perspectives 5 of coordinated development and differentiated development. Based on the theory of regional coordinated development, 6 this paper used panel data for cities in the Yangtze River Economic Belt from 2008 to 2017, adopted the spatial 7 autocorrelation method and spatial econometric model to analyze the spatial and temporal distribution pattern of 8 environmental pollution emission, regional coordination and differentiated development degree in the Yangtze River 9 Economic Belt, analyzed the impact of regional differentiated coordinated development on pollution emission reduction 10 in local and surrounding cities, and discussed the spatial spillover effect of regional differentiated coordinated 11 development on pollution emission and its boundary test. The results showed that (1) at the overall level of the Yangtze 12 River Economic Belt, coordinated regional development and differentiated regional development have significantly 13 reduced pollution emissions and present complementary effects on pollution emission reductions; (2) an obvious spatial 14 spillover effect was observed for the impact of regional coordinated and differential development on pollution reduction, 15 a negative spatial spillover coefficient was observed for different urban economic circles, and an obvious inverted U- 16 shaped trend occurred in the impact degree with increasing distance, with a 500 km range of urban economic circles 17 considered a turning point; and (3) a heterogeneity test used the three major regions and sub-cities of the Yangtze River 18 Economic Belt to verify and analyze the impacts of regional coordinated and differential development on pollution 19 emissions, which showed that there was obvious spatial heterogeneity at different levels. Based on the above results, 20 policy suggestions for decreasing pollution emissions in the process of differentiated coordinated development of the 21 Yangtze River Economic Belt were proposed.


25
In recent years, the National Development Plan proposed that 26 the Yangtze River Economic Belt should be "jointly protected 27 rather than developed" to not only achieve high-quality 28 economic development but also to strengthen ecological and 29 environmental protection to realize the coordinated sources. Yang (2015) found that industrial agglomeration of 73 pollution discharge has inverted U-shaped nonlinear effects, 74 namely, industrial agglomeration at a low level will increase 75 environmental pollution and industrial agglomeration that 76 exceeds a threshold will improve environmental pollution. 77 Shao et al. (2019) found that the energy-saving and emission-78 reduction effects of economic agglomeration may have a 79 significant "inverted N-type" curve relationship and an 80 obvious spatiotemporal dependence. The relationship between 81 economic factor agglomeration and environmental pollution 82 emissions has not yet been determined. Moreover, differences 83 also occur in the environmental spillover effects of economic 84 factor agglomeration on pollution emissions in different 85 regions. Previous studies have focused on analyzing the spatial 86 spillover effects of regional agglomeration on pollution 87 emissions from the overall level; however, the spatial spillover 88 effects of regional agglomeration on pollution emissions 89 within the scope of different urban agglomerations still need to 90 be further explored.

91
Scholars have also studied environmental pollution 92 emissions and their mechanisms from the perspective of 93 regional integration. As market segmentation increases, the 94 gap between regional pollution emissions and energy 95 efficiency has widened (Li and Lin 2017; Hasanbeigi and Price 96 2015) When the degree of market segmentation exceeds a 97 certain limit, regional trade barriers will form and regional 98 development will be inhibited (Lu and  consensus on that regional integration promote the discharge 123 of environmental pollution, few studies have investigated the 124 pollution emission effect of regional differentiated 125 development. Interregional urban integration is a process of 126 "seeking common ground while maintaining differences". 127 However, whether regional coordination and differentiated 128 development can reduce pollution emissions is not clear and 129 the mechanisms that lead to pollution emission reductions 130 have not been identified. Therefore, it is of great significance 131 to study the pollution emission effect from the perspective of 132 regional coordination and differentiated development.

133
This article mainly performs research from three aspects:

134
(1) based on the theory of regional coordinated development, 135 PM2.5 emissions are selected as pollution indicators according 136 to the regional coordination degree and differentiation to 137 discuss the effect of pollution reduction in the development 138 process of "seeking common ground while maintaining 139 differences" among regional cities; (2) the spatial panel Durbin 140 model is adopted to test the coordinated development of the 141 regional differentiation spatial spillover effect on pollution 142 emissions, inspect its spatial spillover boundary, and analyze 143 the change trend of spatial spillover effects as with increased 144 distance; and (3) a multiscale discussion is included on the 145 degree of differentiation and the temporal and spatial 146 differences of pollution emissions in the Yangtze River 147 Economic Belt and the spatial heterogeneity of the impact of 148 regional development on pollution emissions at different levels 149 is verified. The visualization analysis of spatial distribution is 150 carried out in combination with a spatial econometric model. 151

152
According to the "Haken synergy theory", despite differences 153 in the characteristics of each city, there are interactional 154 relationships between cities, including coordination, 155 cooperation and competition, and mutual interference between 156 restricting elements (Haken 1983). Regional development 157 is a process from the integration of independent economic 158 entities into the whole economy, and it emphasizes the organic 159 combination of regional synergy and regional differentiation 160 (Li and Qi 2019; Liu et al. 2019). Regional economic factors 161 influence environmental pollution reduction based on the 162 regional synergy among cities as well as regional 163 differentiation. The development mechanism is shown in 164 Figure 1.

165
First, the efficiency of regional factors must be 166 coordinated to promote energy conservation and emission process of the transferring regional labor factors, the 189 environmental protection concept of immigrants transferred to 190 areas with stricter environmental supervision is increasingly 191 strengthened, which promotes cross-regional dissemination 192 and cultivation of green environment concepts. Third, 193 interregional cooperation and complementarity of resource 194 elements should be promoted. Market segmentation will 195 intensify tax competition among cities, and fiscal 196 decentralization and promotion and assessment by local 197 officials will lead to a "race to the bottom" phenomenon, in 198 which foreign investment will be introduced at the expense of 199 the ecological environment and regions with low economic 200 development will become a "pollution paradise" (Baghdadi et 201 al. 2013), which will have a negative impact on the overall 202 ecological environment. By promoting environmental 203 performance as an important indicator for performance 204 appraisals, regions have focused more attention on overall 205 interests. Local governments will abandon "local 206 protectionism" in favor of resource complementarity, mutual 207 assistance, benefit sharing, and coordinated relationships 208 between economic and environmental development. Moreover, 209 regional cooperation and exchanges accelerate the transfer of 210 economic factors, and cross-regional employment of the 211 population reflects the spillover effect of knowledge and 212 improves the efficiency of production factors. 213 regional coordinated development regional differential development regional development gradually break market segmentation and "local 226 protectionism", promote cross-regional resource integration, 227 save energy and reduce pollution. Moreover, these industries 228 benefit from industrial gradient transfer because new 229 technologies tend to spread gradually from high-gradient 230 regions to low-gradient regions. In addition, the upstream and 231 downstream industries of the Yangtze River Economic Belt 232 have heterogeneity due to regional development differences, 233 which is conducive to industrial gradient transfer and docking. 234 According to their own advantages, local governments should 235 rationally distribute industry to prevent overcapacity caused by 236 industrial structure convergence, maximize benefits, and 237 promote industrial structure optimization and upgrades to 238 reduce pollution emissions. 239 random variable (Dietz and Rosa 1994). In this study, 244 explanatory variables, such as the degree of regional 245 coordinated development and the degree of regional 246 differentiated development, are added, and they are expressed 247 are as follows: 248

Econometric model setting
where represents the amount of pollution 251 emitted by each city; is the regional synergetic 252 degree of each city and other cities in the Yangtze River 253 Economic Belt; is the degree of regional 254 differentiation between each city and other cities in the 255 Yangtze River Economic Belt; * is the 256 interaction term of regional cooperation degree and regional 257 differentiation degree; is the control variable; and is 258 the random error term. 259 According to the above model, a further judgment is 260 made as follows: according to the criteria of the spatial 261 measurement model, the Hausman test, LR test, WALD test 262 and LM test should be used to further determine the model. 263 The verification results are shown in showing that the spatial lag model (SAR) and spatial error 273 model (SEM) are appropriate. In conclusion, the spatial 274 Durbin model (SDM) combining the two spatial models 275 should be used to analyze the regional synergy differentiation 276 development impact on pollution reduction. 277 In summary, the expression of the model is as follows: 278 where is the space weight; represents the spatial 283 autoregression coefficient; and represents the space 284 overflow coefficient. in Table 2. 292 Core variables

296
Regional synergy (ec). The higher the intercity connection, the 297 higher the degree of regional cooperative development; and 298 the greater the geographical distance between cities, the lower 299 the degree of collaborative development between cities (Li and 300 Zeng 2016). The modified gravity model was used to calculate 301 the degree of regional collaborative development between 302 cities and 104 other cities in the Yangtze River Economic Belt: 303 where represents the city, represents other cities in 308 the Yangtze River Economic belt except the city, represents 309 the year, is the population of the city at the end of , 310 is the in year , and represents the geographical 311 distance between city and city . 312 Regional differentiation (dv). The degree of difference 313 between city and 104 other cities in the Yangtze River 314 Economic Belt in year was determined by using the method 315 of Liu and Wu (2017). The specific calculation formula is as 316 follows: 317 represents the employed population of the 319 city in industry in year (the number of employees in 11 320 industries selected to calculate regional differentiation because 321 the number of employees in different industries is frequently 322 missing from statistical yearbooks); and and 323 represent the total number of employees of 11 industries in 324 and cities in year .

325
Pollution degree (pollu) is an index of the serious effect 326 of air pollution on environmental quality, which has attracted 327 wide attention from all walks of life in recent years. Moreover, 328 air pollutants have strong mobility in the region, and the effect 329 of spatial spillover effects is better. Therefore, the annual 330 average PM2.5 concentration is selected as a pollution 331 indicator to measure the degree of regional pollution. Economic Belt. That is, areas with high (low) pollution levels 393 are adjacent to areas with high (low) pollution levels. The data 394 is shown in showing a spatial pattern of "high in the center and low in the 405 surrounding area". As shown in Figure 2 and Economic Belt has been greatly improved, and the degree of 426 pollution in the region has shown an increasing trend from 427 north to south. High-pollution and higher-pollution areas are 428 distributed in the northern part of the lower reaches, such as 429 the Sichuan-Chongqing urban agglomeration, the Yangtze 430 River Delta, and the Yangtze River middle-reach urban 431 agglomeration, indicating that the regional integration of urban 432 agglomerations strengthens the degree of intercity regional 433 connections. The degree of coordination between the north and 434 south in the upper, middle, and lower reaches of the Yangtze 435 River Economic Belt has also been continuously strengthened. 436 For example, the collaboration degree of the middle reaches of 437 the Changsha-Zhuzhou-Xiangtan urban agglomeration and the 438 Wuhan City cycle, the upstream area Sichuan-Chongqing 439 urban agglomeration and Guizhou Province is gradually 440 becoming denser.

447
This article further analyzed the degree of regional 448 differentiation development. As shown in Figure 4, the 449 overall degree of regional differentiation in the Yangtze 450 River Economic Belt from 2008 to 2017 showed a significant 451 downward trend. Compared with regions in the middle and 452 upper reaches of the Yangtze River, the lower reaches of the 453 Yangtze River have a higher degree of differentiation. At the 454 same time, the degree of regional coordination between cities 455 in the lower reaches of the Yangtze River is also high, which 456 further shows that the coordinated development and 457 differentiated development of the region are not in conflict 458 and jointly promote regional development. The provinces in 459 the upper reaches of the Yangtze River are less differentiated, 460 and Hubei Province in the middle reaches of the Yangtze 461 River has a high degree of regional differentiation.  have an agglomeration effect, which is consistent with the 483 conclusion drawn above. The coefficient of regional 484 coordinated development on pollution emissions in the 485 region is negative and passes the significance test of at least 486 5%, indicating that the coordinated development of regional 487 cities has a significant inhibitory effect on pollution 488 emissions; the coefficient of regional differential 489 development on pollution emissions in the region is negative 490 and passes the 5% significance test, indicating that regional 491 differential development has a significant inhibitory effect 492 on pollution emissions; the coefficient of the interaction term 493 between regional coordinated and regional differential 494 development is positive, and both pass the 5% significance 495 test. These findings show that regional coordinated 496 development and regional differentiated development 497 complement jointly promote pollution emission reduction, 498 which has a significant effect on pollution reduction. The 499 regression coefficient of the spatial lag variable is negative, 500 indicating that the coordinated development and 501 differentiated development of the local city have a negative 502 impact on neighboring pollution reduction. 2017). The "Circular Cumulative Causation Theory" states 510 that regional development is not uniformly diffused. Usually, 511 the "central zone" begins to accumulate advantages first and 512 gradually spreads outward through different channels 513 (Krugman, 1991). The Yangtze River Economic Belt spans a 514 wide range, and the impact of regional factor flow on 515 environmental pollution has spatial spillover effects. 516 Drawing lessons from the methods of Yuan et al. (2019) and 517 Dong and Wang (2019), different thresholds were set and a 518 spatial weight matrix was established to discuss the spatial 519 spillover effects of regional coordinated and differentiated 520 development on pollution emissions within the distance of 521 different urban agglomerations. 522 The spatial spillover coefficient passed the 10% 523 significance test within the range of the urban economic 524 groups of 100 to 525 kilometers and became no longer 525 significant after exceeding a range of 525 kilometers. The 526 results are shown in Figure 5. 527 Note: 1) ***, **, and * passed the significance level test at 1%, 5%, and 10%, respectively.
2) The value of t is in brackets.

529
Regional coordinated development and regional 530 differentiated development have exactly the same impact on 531 pollution emissions. As the scope of urban agglomerations 532 expands, differentiated coordinated development has always 533 had a negative impact on pollution emissions from 534 surrounding cities, which further shows that regional 535 coordinated development and differential development 536 complement each other, thereby promoting pollution 537 emissions from surrounding cities. The pollution reduction 538 effect of regionally differentiated and coordinated 539 development shows an inverted U shaped trend. That is, 540 within a certain geographic distance, the spillover and 541 emission reduction of regionally coordinated pollution will 542 first increase and then decrease. Specifically, in the range of 543 100-300 kilometers, regional coordinated differential 544 development has relatively little impact on the pollution 545 emissions of surrounding cities, indicating that the efficiency 546 of pollution reduction in the area of 100-300 kilometers is 547 relatively low. When the spatial distance range exceeds 300 548 kilometers, as the distance range expands, the impact of 549 regionally differentiated development on the pollution 550 reduction effect of surrounding cities is greatly strengthened 551 because the expansion of the spatial range of urban 552 agglomerations is more conducive to local labor cooperation 553 to promote technology spillovers and the upgrade and 554 transfer of industry. A peak is reached within 500 kilometers, 555 and the pollution reduction effect continues to weaken after 556 500 kilometers until the spatial spillover effect is no longer 557 significant. In summary, the verification shows that within 558 different distances, regional coordinated and differentiated 559 development has different spatial spillover effects on 560 pollution reduction. The regression results at the overall level of the Yangtze 567 River Economic Belt indicate that the differential and 568 coordinated development of the Yangtze River Economic 569 Belt has promoted the reduction of pollution and further 570 indicate the impact of regional differentiated coordinated 571 development on pollution emissions in the lower, middle and 572 upper reaches of the Yangtze River Economic Belt. The 573 regression results are shown in Table 5. The coefficient of 574 regional coordinated development and differential 575 development in the lower reaches of the Yangtze River is 576 positive, and the coefficient of the interaction term of the two 577 is negative and passes the 10% significance test. The sign of 578 the spatial lag coefficient is the opposite. It promotes the 579 reduction of pollution emissions in the surrounding areas. 580 The coefficients of regional coordinated development and River is significantly greater than that of the middle reaches 594 of the Yangtze River. 595

598
To further test the spatial heterogeneity of the impact of the 599 differential and coordinated development of the Yangtze 600 River Economic Belt on pollution emissions at the level of 601 different cities, referring to the methods of Yu and Jin (2014), 602 Feng and Wang (2019), the belt cities are divided into four 603 categories for the regression analysis. The results are shown 604 in Table 6. 605 The signs of the coefficients of the coordinated 608 development of mega cities on the pollution of the city and 609 surrounding cities are all negative, with both passing the 10% 610 significance level test, and the coefficients of the two 611 interaction terms are both positive. This finding shows that 612 the coordinated and differential development of mega cities 613 not only promotes the reduction of pollution emissions in the 614 local city but also has spatial spillover effects to reduce 615 pollution emissions from surrounding cities, thus exerting 616 the "scale effect" of mega cities, saving resources and 617 reducing pollution emissions. The results of the coefficients 618 for large and medium sized cities are similar. The impact of 619 regional coordinated development and regionally 620 differentiated development on local pollution emissions 621 passes the 10% significance level test, and the coefficient 622 sign is negative; however, the coefficients of the two on the 623 pollution emissions of the surrounding cities are positive and 624 passed the 10% significance test. This finding shows that the 625 coordinated development of large and medium sized cities 626 has promoted the reduction of pollution emissions in local 627 cities. The coefficients of regional coordinated development 628 and regional differential development in small cities have 629 failed the 10% significance level test, which may be due to 630 the limited spatial scope and low interregional collaboration 631 efficiency. Thus, the differential and coordinated 632 development of small cities has a negative impact on 633 pollution reduction. 634

635
Based on the theory of regional coordinated development, 636 this paper uses panel data of prefecture level cities in the 637 Yangtze River Economic Belt from 2008 to 2017 to analyze 638 the degree of regional coordinated development, the degree 639 of differentiated development, and the temporal and spatial 640 distribution pattern of pollution emissions in the Yangtze 641 River Economic Belt. Based on the Durbin model, this paper 642 used the STIRPAT model to analyze the impact of regional 643 differentiation and coordinated development on pollution 644 emissions and its spatial spillover effects. The analysis 645 results show the following. 646 At the overall level of the Yangtze River Economic Belt, 647 regional differential and coordinated development promoted 648 pollution reduction and improved the ecological 649 environment of the Yangtze River Economic Belt. The 650 effects of regional coordinated development and differential 651 development on pollution emissions are complementary. 652 Regional coordinated and differential development also has 653 a spatial spillover effect on pollution reduction. This effect 654 shows an obvious inverted U shaped trend, with 500 655 kilometers representing the turning point, and the distance 656 range will reduce pollution in the surrounding area before 657 reaching the turning point. The impact continues to rise, 658 although after reaching the turning point, the impact 659 continues to decline and its effect is no longer significant. 660 The heterogeneity test shows that the differential and 661 coordinated development of the middle reaches of the 662 Yangtze River at the three major regional levels of the 663 Yangtze First, the government should acknowledge the synergy 678 among regional cities and strengthen cooperation in regional 679 pollution control. Environmental pollution emissions among 680 urban agglomerations need to be jointly managed, accelerate 681 the process of regional integration, break "local segregation", 682 reduce the mismatch of resource elements caused by market 683 segmentation, establish a pollution emission trading market, 684 and make all regions pay more attention to the overall 685 benefits of the region. Formulate unified environmental 686 governance standards and mutual supervision of the 687 implementation of environmental laws and regulations 688 between governments. 689 Second, the government should focus on regional 690 advantages to promote differentiated division of labor within 691 the region and develop characteristic industries based on 692 local conditions. The government actively guides healthy 693 competition in the market, promotes the appropriate 694 development of industries in various regions of the Yangtze 695 River Economic Belt, and improves overall resource 696 utilization efficiency to achieve emission reduction. The 697 regional industrial gradient transfer should be improved and 698 the upper, middle, and lower reaches of the Yangtze River 699 Economic Belt should be optimized to save the public cost 700 of products and reduce the waste of resources. Products from 701 various regions have achieved complementary advantages 702 via mutual competition and accelerated the upgrading of the 703 industrial structure. The leading role of the regional center 704 should be acknowledged and the transformation of the 705 regional industrial structure to a clean and green industry 706 should be promoted. 707 Finally, the government should fully exploit the role of 708 technological innovation, industrial structure optimization 709 and economic agglomeration in the coordinated and 710 differential development of the Yangtze River Basin. 711 Moreover, low energy consumption and clean industries 712 should be encouraged and promoted to form linkages in 713 different provinces and cities and realize the effect of 714 economic agglomeration to promote cross regional technical 715 cooperation. 716 Author contributions This article was planned and designed by Li-      Spillover coe cient of differentiated coordinated development space in different urban areas