Coupled Energy-Industrial Transitions Shape Heterogeneous Carbon-Air Pollution Cobenefits and Spatial Emission Leakage in China’s Steel Industry

The iron and steel industry is central to industrial decarbonization and air-quality improvement, yet the energy-industrial conditions shaping these outcomes remain insufficiently understood. We develop a unit-level emission database for China's steel industry, covering 2866 enterprises and ∼4030 units, to relate regional energy-industrial configurations to historical driving mechanisms and future mitigation priorities. The sector's CO2 emissions peaked at 1.99 gigatonnes in 2019, while SO2 and PM declined by more than 80% during 2011-2022. Over 2023-2050, production restraint provides the largest projected cumulative CO2 reductions (22.1%), whereas obsolete capacity retirement dominates air pollutant (AP) reductions (22.3%). These priorities vary across regional configurations, exemplified by the greater relevance of process upgrading and capacity restructuring in high-intensity regions. Combined mitigation could lower CO2 intensity to below 1.5 t/t by 2030 and ∼0.6 t/t by 2050. Regionally differentiated pathways may also induce spatial emission leakage, more strongly for CO2 than for APs, although the CO2 leakage ratio declines from 17.39% in 2030 to 2.38% in 2050. Air-quality responses are similarly uneven, with national mean AP concentrations in 2030 decreasing by 5.4-12.3% relative to 2022. The findings suggest that long-process-dependent steel economies require sequenced, regionally differentiated transitions beyond uniform short-process substitution.