Uncovering Synergies in Greenhouse Gas and Air Pollutant Reductions in a Comprehensive Industrial City in Northern China

Coordinated mitigation of greenhouse gases (GHGs) and air pollutants (APs) offers an effective strategy to address climate and air quality challenges, yet systematic evaluations in medium-sized industrial cities remain limited, despite their coal-dependent energy systems and emission-intensive manufacturing that disproportionately shape national emission trajectories. Thus, this study focuses on Weifang, a representative industrial city in Shandong Province, developing a high-resolution, multi-pollutant inventory and applying quantitative synergy indices to characterize emission patterns, sectoral contributions, and hotspot regions. In 2023, Weifang’s total emissions comprised 114.54 million metric tons (Mt) CO2, 121.91 thousand metric tons (kt) CH4, and 27.67 kt N2O, alongside major APs including CO (662.99 kt), TSP (154.44 kt), and NOx (100.83 kt). Industrial sources and electricity-heat production contributed over 80% of CO2 and SO2, while agriculture dominated CH4 (59.5%) and N2O (40.5%). Mobile sources accounted for 66.6% of NOx, over 20% of VOCs, and 61.4% of CO. Spatially, suburban areas produced over 65% of total emissions due to heavy industry and agriculture, whereas the urban core exhibited higher intensities but lower total contributions. Bivariate and integrated synergy indices revealed stronger SO2-NOx-CO2 synergies in the urban core, while suburban emissions were more heterogeneous and spatially dispersed. Synergy analysis indicated strong SO2-CO2 co-variation from shared industrial sources but weak NOx-CO2 correlations due to divergent origins. Hotspot mapping identified industrial parks, power plants, steel zones, and suburban agriculture as priority control areas. These findings demonstrate that source-specific measures are critical to maximizing co-benefits. The proposed methodological framework offers transferable insights for evaluating emission synergies in other industrial cities.