Does Metropolitan Integration Reduce Pollution Inequality? Evidence from Urban Agglomerations in China

Urban integration can lower average pollution, yet environmental benefits may be unevenly shared across cities within the same urban agglomeration. Such within-agglomeration disparities can weaken joint prevention and control, sustain unequal health risks, and hinder inclusive urban sustainability even when overall concentrations fall. Using a panel of Chinese metropolitan areas from 2005 to 2023, we examine whether metropolitan integration is associated with a more even distribution of pollution burdens among constituent cities. We measure within-agglomeration inequality using entropy-based indices for total emissions and emissions intensity, and capture integration intensity using cumulative policy attention and the years since integration began. We find that deeper integration is associated with lower pollution inequality, with larger reductions for inequality in total emissions than for inequality in emissions intensity. The decline emerges after integration begins and persists over time, and it remains robust to alternative measures and to an identification strategy that leverages predetermined historical connectivity. The equalizing association is most evident in metropolitan areas featuring high-primacy and high-ranking core cities, is reinforced by greater fiscal capacity and factor market integration, and is moderated by industrial lock-in. These results suggest that metropolitan integration, when supported by credible cross-city coordination and transition support in regions facing industrial lock-in, can promote cleaner and more equitable environmental outcomes within urban agglomerations.