Nitrite (NO2−), a source of peroxynitrous acid and peroxynitric acid, in plasma-exposed solutions is an important reactant useful for various applications, while its interfacial transfer and generation pathways from plasma to liquids are not fully understood. Experiments using a high-speed pure water jet injected into helium atmospheric-pressure plasma (APP) through a 0.13 mm diameter tube enables the magnication of liquid phase reactions highly localized near the gas-liquid interface and indicates a significant amount of the highly localized reactive NO2− precursor(s). Scavenger experiments revealed that the amount of highly-reactive NO2− precursor(s) reached at least 40% of the total APP-generated NO2−, and it decayed with a half-life of approximately 1 ms. This decay of the highly-reactive NO2−-precursor is in good agreement with the characteristic decay time of cumulative N2O3 signals estimated using a chemical probe DAF-FM. A chemical kinetic model also supports the theory that the primary route to NO2− generation is mediated by the hydrolysis of N2O3, and presents the possibility that the decay of the NO2− precursor may be accelerated by the surface localization of APP-derived species. The presented experimental deduction of the spatial distribution and temporal decay of the APP-generated reactive species, with the aid of a simplified model, can contribute to understanding the interfacial transfer and interconnected chemistry of reactive species at plasma-liquid interfaces.
Takeda et al. (Wed,) studied this question.