The photoemission yield spectroscopy (PYS) study of the 1-year air-exposed thin 16-nm copper phthalocyanine (CuPc) layers deposited on n- and p-type Si (111) native substrates was presented. The occupied electronic states in the band gap and in the upper part of the valence band have been identified from PYS spectra and their possible origin was discussed. Furthermore, space charge layer electronic parameters of organic thin films and their variations upon the exposure were determined. Different values of work function were received as equal 4.64 eV and 4.80 eV for copper phthalocyanine on n-Si substrate and on p-Si one respectively while ionization energies were estimated accordingly as 5.18 eV and 5.21 eV. It was found that after the long term air exposure the work function and surface band bending of CuPc increased by 0.94 eV and 0.56 eV respectively for the layers on n-Si and by 1.05 eV and 0.59 eV for those on p-Si indicated their higher gas sensitivity. Additionally, we detected the significant surface dipole effect on both phthalocyanine samples manifested by strong shift in electron affinity of 0.38 eV and 0.46 eV for layers on n-Si and p-Si substrate respectively. To explain these changes we developed the model of CuPc surface-ambient gas electronic interaction. (C) 2013 Elsevier B. V. All rights reserved.