New experimental evidence on the formation of spatio-temporal concentration patterns as imaged by photoemission electron microscopy (PEEM) supports our earlier kinetic model for subsurface oxygen formation in the CO oxidation reaction on Pt(110). Extensive experimental data on oxygen island growth and conversion is used to derive the activation energy and the preexponential factor for the process of subsurface oxygen formation. We find that under reaction conditions formation of subsurface oxygen may significantly influence properties of traveling concentration waves. Instead of annihilation of two colliding waves, their reflection and two-into-one collision events are observed in the experiments. This behavior is correctly reproduced by the model.