“…According to the "polarization-trickle-down" theory [54,55], the high demand for labor, capital, and other resources in the NU pilot cities will create a "siphon effect", which will deprive the surrounding areas of resources for urban development [56,57]. At the same time, however, the management experience, advanced technology, and important policy implementation knowledge of the NU pilot cities will be transferred to the peripheral regions through the "trickle-down effect", which will reduce the cost of trial and error in the surrounding areas [58,59]. According to the theory of externalities, on the one hand [60,61], the NU pilot cities may eliminate a large number of heavily polluting industries through industrial upgrading in the process of enhancing their own UME, thus reducing the UME of the surrounding areas through pollution transfer [62][63][64]; on the other hand, the improvement of public infrastructure and transport infrastructure in the NU pilot cities will reduce the cost of knowledge flow, thereby better serving as exemplary models and catalyzing agents, and thus enhancing the UME of the surrounding areas [65][66][67].…”