• • Ultra-low emission transformation reduced PCDD/Fs emission concentrations by 86.5% (sintering), 95.1% (converter), and 66.9% (electric arc furnace), with emission factors falling to 0.11, 0.009, and 0.014 μg I-TEQ·t−1 product, respectively—demonstrating process-specific co-benefits that enable compliance with Stockholm Convention obligations.
• • National PCDD/Fs emissions from iron and steel in 2022 under transformation were 104 ± 26 g I-TEQ versus 2049 ± 763 g I-TEQ without, a 94.9% reduction—quantifying the substantial environmental gain and informing inventory updates.
• • Post-transformation congener profiles shifted from high-chlorinated to low-chlorinated dominance, yet 2,3,4,7,8-PeCDF remained the primary toxicity contributor (35%–56%), indicating that toxicity-oriented control must target this specific congener despite overall reductions.
• • Field data from representative processes and air pollution control devices underpin the emission factors, but the lack of post-transformation studies elsewhere limits extrapolation; further on-site measurements are essential to refine national estimates.