The shielding gas composition has a strong influence on the gas metal arc welding (GMAW) process. In particular, CO2 adjunction increases the current needed for the transition from unstable globular to more stable spray transfer. Plasma diagnostic using optical emission spectroscopy was performed using shielding gas composed of argon, argon-CO2 mixtures and argon-N2 mixtures for spray and globular transfer. Radial evolution of the studied parameters was determined thanks to Abel inversion: line broadening was used to get electron temperature and density, and intensity measurement yielded to ratio of neutral and ionized iron over argon. Results showed temperature drop on arc axis in the case of the spray arc transfer. While maximal temperature increases this drop is reduced with nitrogen adjunction and disappears in globular transfer when CO2 rich shielding gas is used. On the contrary, the electron density decreases when CO2 is added to argon. The iron content highest values are observed on the upper part of the column, with overall quantity higher in the case of CO2 containing shielding gas. The obtained data were compared to other recent results dealing with the effect of non homogeneous metal vapour concentration.