Analysis of spatio-temporal dynamics of short-lived reactive species using unique gas-liquid interfacial plasma system*

Gas-liquid interfacial plasmas (GLIPs), in which atmospheric pressure plasmas are in contact with liquid, have attracted great interest worldwide, and applied researches are being conducted in a wide range of fields such as material synthesis, cell function control, and plant growth control. In order to obtain the desired results in these applied researches, it is necessary to control the reactive species produced by the GLIPs, and it is especially important to understand the behavior of short-lived reactive species. In this study, we have developed a unique GLIP system with a high-speed liquid column flow to measure the spatio-temporal distribution of short-lived reactive species in the order of msec [1]. Using this system, we have succeeded in experimentally measuring the fast decay of OH radicals for the first time and analyzing their decay times using a numerical model that takes surface localization into account. Furthermore, we are trying to measure not only OH radicals but also short-lived reactive nitrogen species (RNS). We have successfully measured the time decay of precursors of RNS by using the p-HPA (p-hydroxyphenylacetic acid) as the nitrite/nitrate precursors scavenger. Based on results such as the fact that only the 700 nM of nitrite precursor decayed with a half-life of 3 ms, it was concluded that the precursor of RNS detected in this study was N₂O₃. In order to characterize the short-lived RNS kinetics, we have also built a zero-dimensional model involving 7 equilibrium and 33 non-equilibrium reactions. The calculated time evolution of nitrite formation for initial NO concentration of 700 nM was an underestimate relative to the experimental results. The experimental trend of nitrite formation could be explained by assuming a highly surface-localized distribution corresponding to an initial NO concentration of 10 µM.

[1] K. Takeda, S. Sasaki, W. C. Luo, K. Takashima, and T. Kaneko: Appl. Phys. Express, 14, 056001 (2021).