Importance of nitrite generation route via N<inf>2</inf>O<inf>3,</inf> at plasma-liquid interface

Abstract

Nitrite (NO<inf>2</inf>⁻), 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 NO<inf>2</inf>⁻ precursor(s). Scavenger experiments revealed that the amount of highly-reactive NO<inf>2</inf>⁻ precursor(s) reached at least 40% of the total APP-generated NO<inf>2</inf>⁻, and it decayed with a half-life of approximately 1 ms. This decay of the highly-reactive NO<inf>2</inf>⁻-precursor is in good agreement with the characteristic decay time of cumulative N<inf>2</inf>O<inf>3</inf> signals estimated using a chemical probe DAF-FM. A chemical kinetic model also supports the theory that the primary route to NO<inf>2</inf>⁻ generation is mediated by the hydrolysis of N<inf>2</inf>O<inf>3,</inf> and presents the possibility that the decay of the NO<inf>2</inf>⁻ 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.