City-Level Decision Model and Technology Pathways for Benefit-Oriented Synergistic Control of Air Pollutants and Carbon Dioxide.

Climate change and air pollution control are two urgent global challenges that demand effective solutions. Cities are the fundamental units for implementing control policies of air pollutants and carbon dioxide emissions. However, research on optimized city-level pathways that maximize integrated benefits and synergies of air pollution and carbon reduction remains limited. Here, we develop a decision-making model for coordinated control of air pollutants and carbon dioxide at the city level. The model systematically evaluates the air quality-related benefits, carbon reduction benefits, and their synergies across various emission reduction measures, and uses these evaluations to construct optimized emission reduction scenario under joint air quality and carbon targets. The model is applied to Beijing, Shanghai, and Chengdu: three megacities with populations above 10 million but distinct differences in city functions, industrial structure, and resource endowments. Results show that under enhanced policy regulation, all three cities can achieve national strategy-compliant air quality improvement and carbon reduction. Structural adjustments in energy, industry, and transportation are central to all cities, but priorities vary. Beijing relies on electric vehicles and imported green power; Shanghai focuses on local green power and transportation electrification; Chengdu emphasizes dust control and promoting clean power. Across all cases, monetized benefits exceed costs, though the benefit-to-cost ratio decreases with tightened environmental targets. This research provides methodological tools for improving environmental quality and promoting low-carbon development at the city level, and offers practical references for formulating region-specific policies tailored to local conditions.