As regional integration accelerates globally, green development has emerged as a pivotal imperative for reconciling economic growth with environmental sustainability. This study employs a Difference-in-Differences framework incorporating city and year fixed effects to examine the impact of regional integration on green development efficiency in China’s Yangtze River Delta. The empirical findings reveal that regional integration significantly undermines green development efficiency, a conclusion corroborated by rigorous robustness checks including parallel trends and placebo tests. Mechanism analysis demonstrates that trade openness and digital economy development function as partial mediating channels that modestly attenuate the direct adverse effect of regional integration, whereas the decline in secondary industry agglomeration amplifies the negative impact. Notably, innovation capability has yet to fully unlock its potential for green transformation, it intensifies the negative effects of regional integration across all three mediating mechanisms. Building on these findings, this study proposes policy recommendations including strengthening multi-level green governance frameworks, integrating ecological compensation and carbon trading systems, advancing low-carbon trade structures, promoting the synergistic development of digitalization and green transformation, facilitating the green transition of secondary industries, and reinforcing green technology innovation. These insights provide empirical evidence and policy references for achieving coherence between regional integration and sustainable development objectives.

This study proposes a novel analytical framework that integrates the digital economy, industrial agglomeration, and carbon emissions. It then applies this framework to examine the heterogeneous impacts of secondary and tertiary sector agglomeration on carbon emissions and the moderating role of the digital economy across different city types within the Yangtze River Delta (YRD). The results suggest that secondary sector agglomeration generally increases carbon emissions, while tertiary sector agglomeration reduces them, with variations across city types. In developing cities, secondary sector agglomeration raised carbon emissions between 2010 and 2017, tertiary sector agglomeration reduced carbon emissions until 2019. Super-hub cities exhibited an opposite trend during the 2012 to 2017 period. The digital economy and each of its dimensions positively affect carbon emissions from secondary sector agglomeration but negatively impact carbon emissions from tertiary sector agglomeration to varying degrees. The study thus proposes tailored policy recommendations to promote the synergy of digitalization and green development, as well as the advancement of low-carbon industries.