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Using panel data from 30 provinces in China from 2005 to 2020, this paper uses a spatial double difference model to evaluate the policy impact of the “grain-to-feed” policy on feed grain production in pilot areas and adjacent spatial areas. Research has found that the “grain-to-feed” policy has a significant impact on the feed grain production in pilot areas and can significantly increase the feed grain production in pilot areas by about 2.71 million tons. The “grain-to-feed” policy has strengthened the positive connection between pilot areas and adjacent pilot areas, increased feed grain production, and has a significant spatial spillover effect. Robustness analysis shows that whether using different methods to measure spatial adjacency or using different standards to distribute subsidies, the “grain-to-feed” policy can significantly increase feed grain production, narrow the supply and demand gap of feed grain, and ensure feed grain security. Further analysis shows that the “grain-to-feed” policy can not only ensure the security of feed grain for the current and next periods but also promote the increase in farmers’ income, which is long-term and sustainable. Compared with non-pilot areas, the “grain-to-feed” policy can mitigate the negative impact of wage–price signals on feed grain production in pilot areas. It is recommended that government departments accelerate the transformation of food security concepts, establish a “Big Food Perspective”, gradually promote the pilot of the “grain-to-feed” policy nationwide, increase the subsidy amount of the “grain-to-feed” policy, increase financial support for scientific and technological research and achievement transformation in the field of feed grain, prevent the impact of economic price signal fluctuations on feed grain production, and effectively ensure the security of feed grain in China.

The construction of China’s Free Trade Zone (FTZ) is an important strategy for China’s thorough deepening of opening up and achievement of long-term high-quality development. Based on the panel data of 283 prefecture-level and above cities in China from 2008–2019, this paper adopts the methods of Spatial Differences-in-Differences (SDID), Spatial Differences-in-Differences-in-Differences (SDDD), and spatial intermediary effect test to empirically examine the impact and the spatial spillover of China’s free trade zone on the environmental pollution of the pilot areas and its influencing mechanism. According to the findings of the study, the establishment of pilot free trade zones may suppress urban PM2.5 emissions by around 2.9 percent, and FTZs can also greatly enhance the air quality of neighboring cities. Further examination of the influencing mechanism reveals that the establishment of a FTZ inhibits PM2.5 pollution and has a significant positive spillover on PM2.5 reduction in surrounding cities by the following means: attracting more foreign direct investment; improving the industrial structure through increasing the proportion of tertiary industry; prompting the local government to strengthen environmental regulation as part of the FTZ’s supporting policies; increasing the investment in science and technology innovation, developing scientific and technological level to achieve green production. The empirical results of this paper are still robust after a series of robustness tests when the explained variable is replaced by the traditional air pollution indicator industrial nitrogen oxide emissions, another sort of spatial matrix is introduced, the propensity score matching SDID (PSM-SDID) and placebo tests as well as winsorize method are carried out. Furthermore, the inhibitory effect of FTZs on air pollution is modified by changes in city size, geographic location and city type, according to heterogeneity analysis. Finally, this paper proposes feasible policy recommendations.

Green transformation has become a central goal of China’s development strategy in response to mounting environmental pressure and long-term growth needs. Improving green innovation efficiency (GIE) is essential to achieving this transformation while sustaining economic momentum. This study evaluates the impact of the Pilot Policy for Innovative Industrial Clusters on GIE across Chinese cities. Using panel data from 280 prefecture-level cities between 2007 and 2021, we apply difference-in-differences and spatial difference-in-differences (SDID) models to estimate policy effects, spatial spillovers, and transmission mechanisms. The results are as follows: (1) The pilot policy significantly improves GIE in the pilot cities, with robust results after various tests. (2) The policy enhances urban green innovation through four main channels: reducing energy consumption intensity, upgrading industrial structure, fostering green technological innovation, and accelerating digital infrastructure development. (3) In addition to its direct impact on pilot cities, the policy also boosts the GIE of neighboring cities via spatial spillover effects. (4) Heterogeneity analysis reveals that the policy’s effect is more pronounced in central cities, non-resource cities, and cities with a strong environmental protection focus. This study contributes to the understanding of innovative industrial cluster policies in enhancing GIE and offers valuable policy insights for promoting urban green development.

Utilizing National High-tech Industrial Development Zones (NHIDZs) as a quasi-natural experiment, this study has adopted 285 prefecture and above cities from 2003 to 2018 in China as the research samples and constructed the difference-in-differences (DID) and spatial difference-in-differences (SDID) models to investigate the effects of NHIDZs on economic development and environmental pollution at national, regional, and administrative levels. The results show that NHIDZs have basically achieved a win-win situation in promoting economic development and reducing environmental pollution at the national level. However, spatial heterogeneity is supported at regional and administrative levels. Specifically, “the law of diminishing marginal effect” of NHIDZs is proved in the eastern cities and key cities, which reveals the uneven development pattern of government leading in China, and highlights the importance and necessary of making policy according to local conditions and governing environmental pollution by classification.

The improvement of green innovation efficiency (GIE) in the Yangtze river economic belt (YREB) is beneficial to China’s green transformation and upgrading because of its economic and ecological position. Therefore, based on the slacks-based measure of super-efficiency (Super-SBM) model, the paper studies the GIE and its spatial-temporal variation characteristics in the YREB during the period 2003–2015, and analyzes the spatial correlation and spatial-temporal convergence of GIE with the exploratory spatial data analysis (ESDA) method and convergence analysis method. The results show that the GIE in the YREB shows an “U-shaped” change pattern in time and an extremely unbalanced development pattern in space. The areas with high GIE contribute to the improvement of overall GIE, whereas they do not exert a radiation and driving effect on areas with low GIE. Accordingly, because of the short board effect, the convergent speed of the GIE is decreasing. To be specific, the GIE keeps converging in the upper and lower reaches, except for the year 2010 when GIE in the middle reaches changed from being convergent to being non-convergent. Even though environmental policy exerts great impacts on the improvement of GIE, the lack of collaborative environmental governance leads to the non-convergent and unbalanced development of the GIE. Therefore, green coordinated development of the YREB is necessary.

How to effectively identify the spatial effect of the emissions trading system(ETS) on urban green total factor productivity(GTFP) generated through the linkage of economic factors between cities is a necessary part of scientifically evaluating the effect of ETS policy in emerging- market countries. This study aims to examine the spatial effect, mechanism, and heterogeneity of the ETS on urban GTFP based on the panel data of 281 cities from 2004 to 2017 in China, applying spatial difference-in-differences(DID) Durbin model (SDID-SDM) with multidimensional fixed effect (FE). The results show that ETS significantly improves the GTFP of the pilot cities, produces a spatial spillover effect and the results are robust to the placebo test, propensity score matching SDID (PSM-SDID) test, and Carbon-ETS interference test. Further analysis shows that the policy effect is mainly driven by improving energy efficiency, promoting green innovation, and optimizing the industrial structure. In addition, we found that ETS performs better in regions with a high degree of marketization, strong environmental law enforcement, and a low proportion of coal consumption. In general, the identification method of this study can be used as a scientific reference for conducting similar research in other emerging countries.

We delve into the temporal dynamics of public transportation (PT) ridership in Seoul, South Korea, navigating the periods before, during, and after the COVID-19 pandemic through a spatial difference-in-difference model (SDID). Rooted in urban resilience theory, the study employs micro-level public transportation card data spanning January 2019 to December 2023. Major findings indicate a substantial ridership decline during the severe COVID impact phase, followed by a period in the stable and post-COVID phases. Specifically, compared to the pre-COVID phase, PT ridership experienced a 32.1% decrease in Severe, followed by a reduced magnitude of 21.8% in Stable and 13.5% in post-COVID phase. Interestingly, the observed decrease implies a certain level of adaptability, preventing a complete collapse. Also, contrasting with findings in previous literature, our study reveals a less severe impact, with reductions ranging from 27.0 to 34.9%. Moreover, while the ridership in the post-COVID phase exhibits recovery, the ratio (Post/Pre) staying below 1.0 suggests that the system has not fully returned to its pre-pandemic state. This study contributes to the urban resilience discourse, illustrating how PT system adjusts to COVID, offering insights for transportation planning.

The role of government support in sustainable urban development has always been a research topic of scholars, but research focusing on the relationship between government innovation support and urban green sustainable development is still relatively rare. This article uses China’s innovative city pilot policy (ICPP) to represent the innovation support provided by the government and address the interaction mechanism and the spatial spillover effect of China’s innovative city pilot policy (ICPP), green technology innovation (GTI), and green sustainable development performance (GSDP) with the support of the mediating effect model and the spatial econometric model. Based on panel data of 24 cities in the Yangtze River Delta urban agglomeration from 2001 to 2020, this paper establishes an evaluation index system of green sustainable development performance (GSDP), measuring with the SBM directional distance function based on the undesired output. This paper adopts the spatial difference-in-difference model (SDID) to study the impact mechanism of the ICPP on the GSDP in the Yangtze River Delta. The results show that (i) there is a positive spatial spillover effect of GSDP in the urban agglomeration of the Yangtze River Delta urban agglomeration; (ii) ICPP has a significantly positive effect on GSDP, as verified by several robustness checks; (iii) green technology innovation plays a partial mediating effect in the relationship of the ICPP and GSDP.

Environmental protection and economic development seem to be controversial, and there have been opposite views for a long time. Hence, in this article, representative indicators of economy and environment are selected to analyze the external correlation and the internal relationship between environment and economy from the perspective of coupling coordination. The results show that environmental protection may slow down economic growth in the short term. However, their correlation becomes increasingly stronger with higher degree of coupling, and as the result in the long run, environmental protection can gradually improve the infrastructure of economic development, and environmental and economic development will become more closely coordinated in promoting green economic development. It is demonstrated that an effective way to promoting economic development is to promote scientific and technological innovation and cultivate high-end talents and improve regional cooperation, which can reduce the negative effect of environmental protection on economic development. It is also necessary to enhance the positive impact of environmental protection on economic development by transforming the mode of economic development, developing the environmental protection industry, and raising people’s awareness of environmental protection. Thus, the coupling coordination between environment and economy can sustain, with both continuously bolstered.

Air pollution is a serious environmental problem China has faced in recent years, with winter coal combustion being one of the main sources of air pollution in the northern region. Based on meteorological and economic statistical data from 285 Chinese cities, this study uses the spatial Durbin Difference-in-Difference model to evaluate the actual effect on air quality of the winter clean heating pilot implemented in the northern region since 2017. Our research found that: (1) Pilot policy significantly reduced the level of pollutants in cities, and the air quality index (AQI) score decreased by 3.798. Six air pollutants that make up AQI, including PM 2.5 , PM 10 , SO 2 , CO, and NO 2 , reduced by 5.637 μg/m 3 , 9.724 μg/m 3 , 7.386 μg/m 3 , 0.219 mg/m 3 , and 1.34 μg/m 3 respectively. But O 3 concentration increased instead. (2) The pilot policy has a spatial spillover effect on the emission reduction of several pollutants, but it has not significantly affected the AQI of other cities. (3) By comparing the effect between heating and non-heating periods, the clean heating pilot policy mainly improved the AQI in winter, due to the increased usage of clean energy such as electricity and natural gas. The above results indicate that, as an energy transition project, the clean heating policy in China had a significant effect on relieving air pollution. Developing countries are recommended to accelerate the promotion of clean energy substitution and update facilities to improve energy efficiency, in order to improve local environmental quality and protect the residents’ health.