Spatial spillovers, mediating mechanisms and moderating effects of industrial agglomeration in promoting green total factor productivity

Industrial agglomeration (AGG) reshapes industrial green transformation through the dynamic interplay of economies of scale and congestion effects, yet its nonlinear relationship with green total factor productivity (GTFP) is continuously reconfigured by deepening spatial linkages, energy efficiency evolution, and iterative green economic policies. Leveraging panel data from 279 Chinese prefecture-level cities spanning 2011–2023, this study constructs a Spatial Durbin Model (SDM) and employs comprehensive robustness checks and endogeneity treatments to ensure causal validity. Our findings reveal: (1) a significant U-shaped AGG-GTFP nexus, wherein low-level agglomeration suppresses GTFP while high-level agglomeration fosters it; (2) positive spatial spillovers of GTFP, with neighboring AGG exerting inverted U-shaped effects on local GTFP; (3) energy efficiency serving as a partial mediator; and (4) markedly heterogeneous policy moderating effects—National Pilot Program of Low-Carbon Cities and National Big Data Comprehensive Pilot Zone Policy Green Finance Reform and Innovation Pilot Policy flatten the U-shaped curve, Green Finance Reform and Innovation Pilot Policy steepens it, and Emissions Trading Scheme Pilot Policy demonstrate insignificant moderation. These results furnish theoretical and empirical foundations for staged agglomeration regulation, cross-regional coordinated governance, and precision policy design.