For the oxidation using SO4 -•, a 35 mL heavy-wall glass pressure vessel (Synthware Glass, #P160002D) was loaded with 30 mL of the aqueous solution containing 0.5 mM of individual PFAS and variable concentrations of K2S2O8 (5-100 mM, 10-200 equivalent to PFAS). The initial pH was adjusted by H2SO4 to 2.0. The pressure vessels were covered by a threaded cap, which was not closely tightened to avoid pressure build-up. Multiple vessels were vertically immersed in water inside a 250 mL glass beaker. The beaker was placed in a pressure cooker (Farberware 6 Quart, loaded with 1 L of water), which was heated to 120 ℃ within 20 min and maintained at 120 ℃ for 40 min. The final pH of the reaction mixture went below 2.0. Without the adequate base, the aqueous solution can be further acidified: SO4 -• + H2O → SO4 2-+ HO• + H + For the oxidation using HO•, the reaction settings remained the same except that five molar equivalents of NaOH (relative to K2S2O8) were also added to ensure pH>12.0 throughout the reaction. At alkaline pH, most SO4 -• radicals are converted into hydroxyl radicals (HO•):