Evaluating the Sustainability of Urban Energy Systems: A Policy-Economic-Environmental Analysis of the APPA in China’s ‘2+26’ Cities

In the context of global energy system transformation and the pursuit of regional sustainability, China’s Air Pollution Control and Prevention Action Plan (APPA) targets both pollution reduction and carbon mitigation, serving as a critical policy instrument for coordinating the energy-economy-environment nexus in the “2+26” cities. This study employs a quasi-natural experiment with a difference-in-difference (DID) method to assess the synergistic impact of this energy-related policy on these cities. Results show that APPA significantly reduces PM2.5 and carbon emissions by 5.56% and 9.89%, respectively, demonstrating a successful alignment of short-term environmental targets with long-term decarbonization goals. Heterogeneity analysis reveals that large cities with higher institutional capacity are more effective in reducing both pollutants, while resource-based cities achieve more PM2.5 reduction, and non-resource-based cities excel in low-carbon energy transition. Mechanism analysis indicates that APPA promotes these outcomes by optimizing the energy-intensive industrial structure and fostering green technological innovation. This study highlights the effectiveness of integrated governance frameworks in enhancing air quality and reducing carbon emissions, providing crucial insights for redesigning sustainable energy policies and managing the socio-economic disruptions of just transitions in rapidly developing regions.