Pure and Pd, Pt and Os activated tin oxide thin films have been prepared by the sol-gel process. The physical properties have been investigated by various techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to obtain information on chemical, structural and morphological composition of the layers. In particular microstructure and morphology has been shown to be dependent on the presence of the doping element. Integrated gas micro-sensors were obtained that showed the different sensing characteristics depending also on doping elements. PCA analysis was performed on an array consisting of the prepared sensors and the results have shown the capability to discriminate different air pollutants.