Effect of oxygen concentration on the postdischarge decay of hydroxyl density in humid nitrogen-oxygen pulsed streamer discharge

In this study, the effect of oxygen (O₂) concentration in the range of 0.000 1% (= 1 ppm) to 20% on the decay of hydroxyl (OH) density after pulsed streamer discharge is examined in a humid nitrogen-oxygen mixture under atmospheric pressure. The decay of OH density was measured using laser-induced fluorescence and compared with one-dimensional postdischarge simulations. The simulation results are consistent with the measured decay of OH density for all O₂ concentrations. Essentially, the OH decay was double exponential, consisting of initial rapid decay for t < 0.1 ms and subsequent slow decay for t > 1 ms, where t represents the postdischarge time. In the slow decay phase, O₂ change in the order of 10 ppm markedly affected the OH decay rate when O₂ < 100 ppm. The sensitive effect of the small amount of O₂ can be attributed to the reaction, $H+O_2+M\to {HO}_2+M$, which converts H atoms to HO₂, and the subsequent OH production via H+HO₂→ OH+OH. Other production and loss processes of OH in the postdischarge phase were also examined. (paper)