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The chemical properties of the gaseous species generated in a humid air gliding arc discharge are investigated. Aqueous solutions are used as the targets exposed to the plasma, and this allows to evidence strong acid and oxidizing effects on various solutes by means of spectrometric or potentiometric methods. The influence of some working parameters such as the input gas flow, the distance from the electrodes to the target or the electrode gap is examined on the chemical transform and simple experimental laws are derived. A general feature is observed for oxidation and suggests the occurrence of an auto-catalytic step in the relevant kinetic mechanism.

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Electric discharges burning in humid air at atmospheric pressure over aqueous solutions induce acid effects in the liquid phase resulting from the formation of nitric acid and peroxynitrous acid as transient precursor. These acid effects affect the degradation mechanisms of organic wastes and the relevant kinetic rates; therefore they thus must be controlled (e.g. using buffers). Nitrogen reactive species such as peroxynitrous acid or its salt are directly concerned with both acid effects as precursor to nitric acid, and strong oxidizing properties E • (ONO 2 H/NO 2 ) = 2.02 V/SHE. Illustrating examples are given in the case of an organic dye (Alizarin S) removal and the gliding discharge treatment of urban wastewaters. Additional arguments are presented to explain the biocidal effect of humid air discharges.

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