An atmospheric pressure CO2/Ar plasma is produced using an ICP torch. This plasma is passed at high velocity through a water-cooled test-section that forces rapid cooling and recombination. At the water-cooled test-section inlet, the plasma is close to Local Thermodynamic Equilibrium at about 6750 K. The subsequent thermochemical evolution of the plasma at it traverses the water-cooled tube is studied using Optical Emission Spectroscopy from the UV to NIR. The measured spectra, calibrated in absolute intensity, are compared with calculations done using the SPECAIR line-by-line radiation code. At the exit of the 15-cm water-cooled tube, the centerline temperature is found to have dropped to 6100 K. Indications of thermochemical non-equilibrium are found in the emission spectrum at the exit of the tube. The measurements presented here are meant to provide a test case for comparison with theoretical predictions made by kinetic models and/or CFD predictions.