Impact Assessment and Mechanism Disentangling of "Zero-Waste City" construction policy on Carbon Emission Efficiency

Against the backdrop of deteriorating global ecological environments and intensifying resource constraints, China, as one of the world's largest emitters of carbon and producer of solid waste, faces increasingly prominent dual pressures from solid waste pollution and carbon emissions. This presents severe challenges that necessitate effective policy tools for synergistic pollution and carbon reduction. This study focuses on the "Zero-Waste City" initiative as such a policy tool, systematically dissecting its complex impact on carbon emission efficiency. Urban carbon emission efficiency was calculated using the non-radial super-efficiency SBM model with undesirable outputs. Leveraging China's "Zero-Waste City" policy as a quasi-natural experiment, a difference-in-differences (DID) model was constructed to assess the policy's net effects and uncover multidimensional driving pathways. The results indicate that: (1) The "Zero-Waste City" initiative significantly improved carbon emission efficiency, increasing it by an average of 0.122 units in pilot cities. (2) Mechanism analysis reveals that the initiative, oriented toward source reduction of solid waste, promotes green industrial transformation by reducing waste disposal volumes and associated energy consumption, thereby achieving synergistic pollution and carbon reduction. Moreover, by prioritizing the resourceful utilization of solid waste, it drives green technological innovation, enhances efficient resource conservation, and improves urban carbon emission efficiency through substituting raw materials and fossil fuels with recycled waste materials. (3) Heterogeneity analysis shows that the policy effects vary significantly, with more pronounced improvements in carbon emission efficiency observed in cities in eastern regions, resource-based cities, and large-sized cities. Based on these findings, recommendations include strengthening top-level design and regionally differentiated coordination; precisely targeting industrial transformation and technological innovation as two core pathways; and promoting city-specific implementation models while enhancing capacity building. This study provides empirical evidence for optimizing and scaling up the "Zero-Waste City" policy, offering valuable insights for advancing synergistic pollution and carbon reduction and achieving the dual-carbon goals.