In this work, the effect of electrical discharge on nitrate concentration is considered in aqueous solution. The atmospheric pressure plasma was produced by a high-voltage power supply at 27 kHz using pin-to-pin configuration. Air, argon, and argon/methane mixture were used to study the working gas effect. UV-VIS spectroscopy and ion chromatography were used to analyze the effect of the electrical discharge on nitrate concentration in deionized water. Optical emission spectroscopy (OES) was applied to diagnose active species inside and on the surface of the deionized water solution. The results of the present work showed that the atmospheric pressure electric discharge with air increases nitrate concentration while it remains constant using argon and argon/methane electrical discharges. It was also revealed that in the presence of air, the electrical discharge reduces pH, acidifying the solution and increasing solution conductivity due to production of extra nitrate ions. On the other hand, argon electrical discharge increases pH and conductivity due to production of OH- ion in water.
