After switching to EO mode, all surfactant molecules degraded to non-detected after 40 h (i.e., 16 h under EO, Fig. ). In comparison, most targeted PFAS structures showed concentration increases sooner or later (Figs. ), and eventually became non-detected after 44 h (i.e., 20 h under EO). In particular, elevated PFCAs showed the generation-degradation profiles in a wide time window (Fig. versus Fig. ), indicating the oxidative transformation of the abundant FT surfactants. The early generation of n=5 PFHxA, n=4 PFPeA, and n=3 PFBA in high concentrations suggest the oxidative conversion of the dominant n=6 FT precursors, as revealed by F NMR (Fig. ). The oxidation of pure n=6 FTS using HO• radicals yielded similar PFCA product distributions (i.e., "n-2 dominance" rule). The second wave of PFCA generation started after 32 h, with the most significant increase for n=6 PFHpA, followed by n=5 PFHxA and n=7 PFOA, suggesting a slower oxidative conversion of n=8 FT precursors. The increase of n=6 and 8 FTSs during EO treatment (Fig. ) suggested the oxidation of organic moieties. The very short time window for PFSAs (Fig. ) further confirmed that sulfonamide precursors were minor components in the studied AFFF, and all degraded within a few hours. After the EO treatment, all targeted PFAS were below the detection limits shown in Table . The F -ion release reached ~100% of overall defluorination (Fig. ). F NMR analysis of the residual also found no other F resonance beside F -(Fig. ), which is another evidence for the near-quantitative defluorination.