An investigation of the vapor phase concentration is performed using the Infrared Absorption technique on a gas/droplet flow in a heated real-scale environment. Experiments are carried out in a rectangular chamber with optical access. The injection system is composed of a pressure atomizer and an air swirler. The first part of the paper describes the fundamentals of the measurement technique and the experimental procedure. To obtain spatially resolved results, a deconvolution procedure needs to be applied to the raw data. A modified version of the Abel algorithm is proposed. Then, steady measurements performed downstream from the injector provide the radial and longitudinal evolution of the vapor mass fraction. Varoius operating air temperatures are investigated. A spectral analysis of time resolved recordings shows that the liquid droplets are moving with the frequency of the Processing Vortex Core (PVC). Finally, the results are discussed and some future developments of the method are proposed.