The impact of the zero-waste city pilot policy on the synergistic reduction of CO₂ and air pollutant emissions: evidence from China.

Against the backdrop of China's carbon peaking and carbon neutrality agenda and intensified pollution control efforts, advancing the synergistic control of CO₂ and air pollutant emissions has become an important pathway toward green transformation and the reduction of environmental health risks. Using panel data for 286 prefecture-level cities in China from 2011 to 2022, this study treats the zero-waste city pilot policy as a quasi-natural experiment and applies a double machine learning framework to identify its impact on urban synergistic outcomes in CO₂ and air pollutant emission control. The results show that: (1) the zero-waste city pilot significantly improves the synergistic control of CO₂ and air pollutant emissions, and this finding remains robust across multiple checks; (2) the policy effect operates mainly through source reduction, resource recycling, and high-standard harmless treatment; and (3) the effects are more pronounced in central and western regions, in small- and medium-sized cities, and in non-resource-based cities. Overall, this study provides new evidence that integrated environmental governance can simultaneously promote environmental sustainability and public health improvement.