A process for the conversion of N.sub.2 O into NO.sub.x (x=1 or 2) thereof, comprising forming a jet of gas to be treated comprising N.sub.2 O and directing the jet into the interstitial space of at least two divergent electrodes placed under an electric voltage, to create at least one electric discharge and/or arc, and is part of a low-temperature plasma generator. The generator works by formation of electric discharges sliding between the electrodes such that the gas circulates along the electrodes from the discharge region where these electrodes are closest to each other. Finally, the NO.sub.x gas formed is recovered. The invention also relates to a device for carrying out the process.