Spatiotemporal Evolution, Regional Disparities, and Driving Factors of Synergistic Pollution and Carbon Reduction in Shandong Province Under China’s Dual-Carbon Targets

Synergistic pollution and carbon reduction is central to China’s Dual-Carbon strategy, yet the structural constraints on its regional evolution remain insufficiently examined. Using panel data from 16 prefecture-level cities in Shandong Province over 2010–2023, this study combines a coupling coordination degree model, Dagum Gini coefficient decomposition, and a panel fixed-effects model. Three findings emerge. First, the coupling coordination degree rose from 0.760 to 0.847, but this improvement was driven almost entirely by pollution reduction. The pollution reduction composite index increased by 31.7%, whereas the carbon reduction composite index declined by 6.6%, producing a pronounced “rapid pollution reduction, stagnant carbon reduction” asymmetry. Second, the spatial pattern was characterized by city-level differentiation rather than an east–west gradient, with Binzhou and Rizhao lagging persistently. Third, the Dagum Gini coefficient declined from 0.088 to 0.068, with transvariation intensity remaining the dominant source of disparity throughout the period (contributing 40.6–63.6%), indicating the limited explanatory power of the circle-based classification. Energy intensity and secondary industry share were the most robust drivers, whereas R&D intensity was statistically indistinguishable from zero. Policy should therefore prioritize energy efficiency improvement and city-specific targeting of persistently lagging cities.