Spectroscopic measurements were made on a nitrogen nonblown arc in extinction at atmospheric pressure seeded with copper vapor produced by the anode. The experimentally determined axial temperatures and total line intensities were compared to theoretical values obtained from a model based on mass and energy conservation equations. This comparison validated the model and showed that for an initial current of 25 A, the concentration of copper decreases at 0.5 mm from the anode as soon as the electric field is cut but remains more or less constant for about 150 &mgr;s in the region of plasma at around 2.5 mm from the anode. This is mainly due to the copper diffusion mechanisms involved. The model allowed the influence of copper on the evolution of the conductance of a nitrogen arc during extinction to be calculated. In particular it was seen that a proportion of copper as low as 10−4markedly changed the conductance of the arc. Moreover, when the conductance of pure nitrogen has dropped by a factor of 40 compared to the initial value, that of a mixture containing 99.9% nitrogen and 0.1% copper has only decreased by a factor of 4.