Generation of nitric acid and nitrous acid in distilled water irradiated with atmospheric-pressure plasma jet

Abstract

An atmospheric-pressure argon (Ar) plasma jet was directly irradiated onto distilled water. Semiquantitative determination using test strips and flow injection analysis (FIA) revealed that nitric acid (HNO3 ) and nitrous acid (HNO2 ) were generated in distilled water by plasma jet irradiation for 1 min. The nitrate ion (NO3-) and nitrite ion (NO2-) concentrations in distilled water irradiated with a plasma jet, determined from the test strips, were in good agreement with those determined by FIA. The NO3-concentration in distilled water proportionally increased with the plasma irradiation time, whereas the NO2-concentration was almost unchanged. It is considered that high-energy electrons in the plasma jet collided with nitrogen molecules (N2 ) and oxygen molecules (O2 ) to generate nitrogen (N) and oxygen (O) radicals. Nitrogen oxide (NxOy ) generated upon the reaction of the radicals is considered to react with water molecules (H 2O) in air and at the surface of distilled water to generate HNO3 and HNO2 .