The effect of humidity on the discharge mode transition of air discharge plasma

Cold atmospheric plasma in air commonly operates in the O-3 mode and NOx mode, which easily interconvert through a transition mode, depending on discharge conditions. Given that the humidity varies considerably in different weather, it is important to elucidate the effect of humidity on the discharge mode transition, but few studies have been reported thus far. In this study, air plasmas were generated by a surface dielectric barrier discharge with different discharge powers of 6, 9, and 12 W, and the relative humidity of air was controlled at 1.5% (dry air), 40%, or 80% for a comparative study. It was found that an increase in humidity suppressed the production of O-3 but promoted that of NO2 when the discharge power was 6W, whereas it promoted the production of O-3 but suppressed that of NO2 when the discharge power was 12 W. This implies that air humidity could have a bidirectional effect on the discharge mode transition, which was validated by experiments with a moderate power of 9W. In that case, the discharge in dry air maintained the transition mode at a quasi-stable state, but it transited either into the NOx mode when the humidity was 40% or into the O-3 mode when the humidity was 80%. A competition between reaction pathways dominated by N-2(nu) or water-originated compounds may be the cause, and our findings indicate that the effect of humidity should be taken seriously in the research and development of air discharge plasmas.

Automated summary

This study investigated the effect of humidity on the discharge mode transition in air plasmas generated by surface dielectric barrier discharge. The research found that humidity has a bidirectional effect on the production of O-3 and NO2 in the discharge, indicating its influence on the discharge mode transition. The competition between reaction pathways dominated by N-2(nu) and water-originated compounds may be the cause of this bidirectional effect.