Effect of gas components on the post-discharge temporal behavior of OH and O of a non-equilibrium atmospheric pressure plasma driven by nanosecond voltage pulses

OH radicals and O atoms are two of the most important reactive species of non-equilibrium atmospheric pressure plasma (NAPP), which plays important role in applications such as plasma medicine. However, the experimental studies on how the gas content affects the post-discharge temporal evolution of OH and O in the noble gas ns-NAPP are very limit. In this paper, the effect of the percentage of O2, N2, and H2O on the amount of OH and O production and their post-discharge temporal behavior in ns-NAPP is investigated by Laser-induced fluorescence (LIF) method. The results show that the production of OH and O increases and then decreases with the increase of O2 percentage. Both OH and O densities reach their maximum when about 0.8% O2 is added. Further increase the O2 concentration results in the decrease of the initial densities of both OH and O, and leads to their faster decay. With the increase of N2 percentage, it also results in the increase and then decrease of the OH and O densities, but the change is smaller. Furthermore, when the H2O concentration is increased from 100 ppm to 3000 ppm, the initial OH density increases slightly, but the OH density decays much faster. While the initial density of O decreases with the increase of the H2O concentration. After analysis, it is found that OH and O are mainly produced through electron collisional dissociation. O (1D) is critical for OH generation. O3 accelerates the consumption process of OH and O at high O2 percentage. The addition of H2O in the NAPP considerably enhances the electronegativity, while it decreases the overall plasma reactivity, accelerates the decay of OH and reduces the O atom density.