A combined atomic nitrogen‑oxygen OES line-ratios method to determine the low-energy and high-energy electron temperature in non-equilibrium atmospheric pressure air glide arc plasmas

Atmospheric pressure air plasma is widely used in material processing, plasma-assisted combustion, life science and agriculture. The active-particle density is considered a key factor in monitoring the plasma states, and it is related to the electron temperature. However, there is a lack of an efficient optical emission spectroscopy (OES) method to obtain the electron temperature in atmospheric pressure non-equilibrium air plasma, especially when the electron energy distribution deviates from the Maxwellian distribution. So, in this work, we propose a novel combined OES line-ratios method to determine the high/low-energy electron temperature. This method is based on two summarized excited-state systems, the “N(2p^{3 4}S^o) excited-state system” and “O(2p³(⁴S^o)3s ⁵S^o) excited-state system”, which are presented to find key excited-states sensitive to the high/low-energy electron temperature, respectively. Besides, a collisional-radiative model, considering the atomic nitrogen and oxygen including their excited states, is built to provide the mapping relation and verify the kinetic properties from the above excited-state systems. Our combined line-ratio method has been applied in an air glide arc plasma igniter.