Types identification, patterns characterize and pathway optimization of synergistic development between urbanization and pollution control in Chinese urban agglomerations

Against the backdrop of China's carbon peaking and neutrality goals, the way urban agglomerations coordinate rapid urbanization with pollution control has direct implications for energy use and the low-carbon transition. Yet evidence at the urban-agglomeration scale remains limited: synergy is often reduced to an overall score or coarse category, within-agglomeration spatiotemporal patterns are rarely integrated, and policy implications stay generic because outcomes are seldom linked to subsystem-level drivers. To address these gaps, this study examines nineteen major urban agglomerations in China and develops a unified evaluation and diagnostic framework that supports comparable city-level type identification, agglomeration-scale spatiotemporal mapping, and subsystem-based explanation of coupling outcomes. Using a consistent indicator system, we first apply the entropy-TOPSIS method to measure city-level urbanization and pollution control, then construct a coupling-coordination typology and track the spatiotemporal evolution of coordination types within and across agglomerations. We further decompose subsystem influences to identify binding constraints and derive agglomeration-specific optimization directions. The results show that: (1) most cities are concentrated in medium-level development patterns, with clear within-agglomeration heterogeneity and core-periphery gradients; (2) coupling coordination improves over time but remains generally weak, with progress concentrated in core cities and slow diffusion to surrounding cities, so maladjustment persists widely; and (3) coordination outcomes are constrained by asymmetric subsystem influences, meaning that at least one subsystem in most agglomerations persistently acts as a bottleneck. Overall, the study provides a reproducible basis for diagnosing where and why synergy remains weak and for designing differentiated, subsystem-targeted pathways to support greener and lower-carbon development in China's urban agglomerations.