“…However, it is difficult to detect the emission of OH(A-X) at 308 nm, which has been also reported in other work (Ye et al, 2017). It was probably due to the fact that the quenching of excited OH radicals by oxygen, nitrogen and water molecules is much faster than the de-excitation processes to the ground state (Sun et al, 2005;Yao et al, 2016), making it very difficult to observe OH in the spectra, although it is certainly that OH radicals are present in air/H 2 O plasma discharge. On the other hand, the excited oxygen atoms at transition 5 S 0 / 5 P, 777 nm can be observed in Fig.…”