In this study indoor and outdoor air carbonyl compounds concentrations data are processed by means of principal component analysis (PCA). The analysis pointed to the carbonyl compounds sources as well as to their mutual interrelations. A global six sources (components) solution, accounting for the joint variability of the measured variables, was obtained. The existence of a linear function connecting outdoor and indoor components allowed for an exchange model between indoor and outdoor carbonyl compounds to be outlined. The different sources of carbonyl compounds were tentatively identified. Overall, this work demonstrates the presence of a delicate balance between indoor and outdoor carbonyl compounds contamination with the two compartments (indoor and outdoor) engaged in a close relationship.