How does regional integration policy affect urban energy efficiency? A quasi-natural experiment based on policy of national urban agglomeration

This paper is based on panel data at the city level in China and employs the Meta-frontier and Nonradial Directional Distance Function (MNDDF) method to measure urban energy efficiency. Meanwhile, the multi-period difference in difference (DID) model is used to evaluate the impact and mechanisms of regional integration policy (RIP) on the urban energy efficiency. The study found that: (1) RIP significantly enhance urban energy efficiency, a conclusion that remains robust after placebo tests, endogeneity tests, and the exclusion of other policy interferences. (2) Heterogeneity tests reveal that RIP significantly improve energy efficiency in the central and western regions, non-resource-based cities, and small and medium-sized cities, but have no significant effect on the eastern regions, resource-based cities, and large cities. (3) Nonlinear regression results indicate that the marginal effects of RIP on urban energy efficiency vary dynamically at different levels of efficiency. (4) Spatial effect tests show that while RIP significantly promote energy efficiency within the region, the presence of a "siphon effect" somewhat inhibits energy efficiency improvements in neighboring areas. (5) Mechanism analysis indicates that RIP affect urban energy efficiency through green technological innovation and industrial agglomeration. Furthermore, when comparing different urban locations and city sizes, industrial agglomeration is the primary mechanism by which RIP differently affect urban energy efficiency. In contrast, when comparing different urban attributes, both green technological innovation and industrial agglomeration are the main mechanisms through which RIP exert varying impacts on urban energy efficiency. (6) Extended analysis demonstrates the objective existence of regional convergence in urban energy efficiency and shows that RIP not only promote improvements in urban energy efficiency but also positively influence its convergence. This research contributes nuanced insights that inform policymakers, practitioners, and scholars about the strategic design and scaling of RIP in diverse urban contexts.