The surface of a Pyrex discharge tube was treated by a capacitively coupled RF plasma at low pressure. In cases where the plasma contained oxygen, O atoms deposition on the tube surface could be confirmed via the time-dependent conversion of NO to NO2 in a post-plasma experiment. Inside the discharge tube, the evolution of the concentrations of NO and of NO2 was measured using quantum cascade laser absorption spectroscopy in the mid-infrared spectral range. The surface density of atomic oxygen was estimated to be about 2 × 1014 cm-2 based on NO oxidation in the closed reactor. The production rate of NO2 is in the range of 2 × 1011 molecules cm-3 s-1.