Analysis of policy synergy and its influencing factors in the construction of zero-waste city in China

The construction of a zero-waste city(ZWC) is a key strategy to address resource scarcity and achieve synergies in pollution reduction and carbon mitigation, making an accurate assessment of inter-city policy synergy (ICPS) and its drivers urgent. We develop a policy synergy indicator (PSI) using text mining and complex network analysis, applying the quadratic assignment procedure (QAP) model to examine the effects of political, economic, social, infrastructural, and geographic proximity factors on ICPS. We find that (1)ICPS varies substantially, with the strongest synergy observed between Shanghai and Tianjin, Ningbo, and Beijing, reaching values of 0.667, 0.665, and 0.604, respectively. Among the three key regions, the Yangtze River Delta (YRD) exhibits the highest level at 0.299, while the Pan-Pearl River Delta (PPRD) shows the lowest at 0.247. (2) All five dimensions significantly influence ICPS, particularly for mandatory policies and large cities. The administrative hierarchy exerts the strongest effect, whereby a 1% increase raises ICPS by approximately 0.406%. (3)The mechanisms promoting ICPS differ regionally. The Beijing-Tianjin-Hebei region and its periphery (BTH) rely primarily on administrative hierarchy and economic development, whereas the YRD and PPRD benefit from geographic proximity. These findings contribute to improving ICPS in the construction of ZWC.