The impact of heterogeneous environmental regulation on the energy eco-efficiency of China's energy-mineral cities

The improvement of energy eco-efficiency (EEE) is the key to achieving coordinated and sustainable develop-ment of China's energy economy and environmental protection. Under ecological constraints, effective envi-ronmental regulations have become an important method to promote Pareto optimization of energy resources. Based on the panel data of China's 31 energy-mineral cities in 2007-2018, the energy eco-efficiency is evaluated, Tobit regression and threshold regression models are constructed to test the effects of heterogeneous environ-mental regulations on energy eco-efficiency. The results show that: Energy eco-efficiency increased from 0.333 to 0.678 in 2007-2008, and the growth of energy eco-efficiency is the most significant in eastern China; compulsory environmental regulations (CER) and market-incentive environmental regulations (MER) will inhibit energy eco-efficiency, and the inhibitory effect is more obvious in central and northeastern regions; voluntary environmental regulations (VER) have a time lag in inhibiting energy eco-efficiency. There is a single threshold for the impact of compulsory and market-incentive environmental regulations on energy eco-efficiency. Voluntary environmental regulations have the double threshold, and they can promote energy eco-efficiency only within the threshold range. These findings indicate that the effects of different environmental regulations on EEE differ by region and have different thresholds. Therefore, the environmental regulation tools are improved by enhancing the envi-ronmental information disclosure mechanism, the eco-welfare-oriented appraisal mechanism and the system of rewards and punishments for technological innovation. Furthermore, multiple environmental regulation tools can be flexibly adjusted to effectively improve EEE based on the characteristics and realities of different regions.