Importance of nitrite generation route via N₂O₃ at plasma-liquid interface

Nitrite (NO 2 − ), 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 0.13-mm diamter tube enable to magnify liquid phase reaction highly localized near the gas-liquid interface and indicate significant amount of the highly localized reactive NO 2 − precursor(s). Scavenger experiments revealed that the amount of highly-reactive NO 2 − precursor(s) reached at least 40% of the total APP-generated NO 2 − , and it decayed with a half-life of approximately 1 ms. This decay of the highly-reactive NO 2 − -precursor was in good agreement with the characteristic decay time of cumulative N 2 O 3 signals estimated using a chemical probe DAF-FM. A chemical kinetic model also supports that the primary route to NO 2 − generation is mediated by the hydrolysis of N 2 O 3 , and presents the possibility that the decay of the NO 2 − precursor may be accelerated by the surface localization of APP-derived species. The presented experimental deduction on the spatial distribution and temporal decay of the APP-generated reactive species, with an aid of simplified model, can contribute to understanding interfacial transfer and interconnected chemistry of reactive species at plasma-liquid interfaces.