Multi-objective analysis of the co-mitigation of CO₂ and PM_2.5 pollution by China's iron and steel industry

China has experienced serious fine particulate matter (PM_2.5) pollution in recent years, and carbon dioxide (CO₂) emissions must be controlled so that China can keep its pledge to reduce CO₂ emissions by 2030. The iron and steel industry is energy intensive and contributes significantly to PM_2.5 pollution in China. The simultaneous reduction of CO₂ emissions and PM_2.5 pollution while minimizing the total mitigation costs remains a crucial issue that must be resolved. Using a multi-objective analysis, we compared potential technology combinations based on various policy preferences and targets. Our results showed that policies designed to mitigate PM_2.5 pollution have substantial co-benefits for CO₂ emissions reductions. However, policies focused solely on reducing CO₂ emissions fail to effectively reduce PM_2.5. Furthermore, CO₂ emissions reductions correspond to large financial costs, whereas PM_2.5 pollution reductions are less expensive. Our results suggest that under limited budgets, decision makers should prioritize PM_2.5 reductions because CO₂ reductions may be simultaneously achieved. Achieving large decreases in CO₂ emissions will require further technological innovations to reduce the cost threshold. Thus, China should focus on reducing PM pollution in the short term and prepare for the expected challenges associated with CO₂ reductions in the future.