*Limitations and Outlook*

This paper mainly explores the impact of environmental regulation on China's regional green development from the governance transformation perspective. Although this study provides valuable insights, it still has certain limitations, which could also be directions for future research. First, owing to the difficulty in collecting relevant data, the sample period of this paper spanned from 2003 to 2017. Specifically, when calculating the GTFP growth of China's 30 provinces, the data of these variables, such as gross industrial output, industrial sulfur dioxide, and industrial sewage emissions, were only updated to 2017. The index of environmental regulation, namely, the amount of industrial pollution control investment, lacks the data for 2018 in all provinces. If additional data had been available, the conclusions would be richer and more reliable. Future research can make progress on data expansion. Second, while this study investigates the nonlinear relationship between environmental regulation and GTFP in an empirical analysis, its driving mechanism and dynamic evolutionary paths have not been clearly explored, which is limited by sample data acquisition. Therefore, the follow-up studies can attempt to establish theoretical models (e.g., the dynamic stochastic general equilibrium model), which could be used to describe the dynamic transmission mechanisms of environmental regulation and governance transformation on GTFP, as well as providing a sound theoretical basis for the empirical results of this paper. Third, the dynamic panel GMM model used in this paper ignores the spatial effects of environmental regulation. However, due to the externality

of environmental pollution, there are obvious imitation behaviors and strategic games in inter-regional environmental regulation, which inevitably engenders spatial spillover effects. In the future, we plan to divide environmental regulation into administrative environmental regulation and market-based environmental regulation. This will enable the construction of a dynamic spatial panel GMM model to investigate the direct and indirect effects of different types of environmental regulation on GTFP. Finally, this study uses provincial-level data, and its availability is limited. To be specific, due to the remarkable differences in economic development levels across different cities within a province, it is meaningful and reasonable to explore the relationship among environmental regulation, governance transformation, and the GTFP for different regions when city-level data are available in the future. Specifically, the use of city-level data can not only control the potential heterogeneity across cities within a province, but it can also enhance the credibility due to the significant expansion of the sample size.

**Author Contributions:** Article research framework design, X.X.; empirical model construction, X.X., X.L. and L.Z.; raw data collection and data processing, X.L. and L.Z.; writing and translating, X.X. and L.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is sponsored by the National Social Science Foundation of China (No. 19BRK036), the Humanities and Social Science Youth Foundation of the Ministry of Education in China (No. 18YJC840047), and the Social Science Foundation of Hunan Province (No. 17YBQ104).

**Institutional Review Board Statement:** This study did not involve humans. No statement from the institutional review board is required.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The datasets and computer programs used in this study are available from the corresponding author upon reasonable requests.

**Acknowledgments:** We are sincerely grateful to the editor and anonymous referees for their insightful remarks and suggestions. They make some pertinent comments on the previous version of this paper, and also give us some suggestions and hints. We also would like to thank Junqi He, Yan Qu, Jia Song and Cui Yuan for their research assistance. Nevertheless, any errors that remain in this paper are solely our responsibility.

**Conflicts of Interest:** The authors declare no conflict of interest.
