analysis was performed to study the plasma excitation process with and without catalyst. The results are shown in Fig. . The overall OES spectrum for ammonia synthesis from different routes are well-detected (Fig. ). Noticeably, the main nitrogen oxide product detected was nitrous oxide (N2O), as shown in (Fig. ). Other nitrogen oxides such as NxOy were possibly generated but within concentrations below detection limits. Compared with the plasma-only experiments, the catalyst-plasma experiment for ammonia synthesis from N2 and sea water vapor exhibited insignificant differences in the intensity of the N2O-related peaks (Fig. ).