Atmos. Chem. Phys. Discuss., 11, 27861-27885, 2011
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Interaction of NO2 with TiO2 surface under UV irradiation: measurements of the uptake coefficient
A. El Zein and Y. Bedjanian
Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS, 45071 Orléans Cedex 2, France

Abstract. The interaction of NO2 with TiO2 solid films was studied under UV irradiation using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The NO2 to TiO2 reactive uptake coefficient was measured from the kinetics of NO2 loss on TiO2 coated Pyrex rods as a function of NO2 concentration, irradiance intensity (JNO2 = 0.002–0.012 s−1), relative humidity (RH = 0.06–69%), temperature (T = 275–320 K) and partial pressure of oxygen (0.001–3 Torr). TiO2 surface deactivation upon exposure to NO2 was observed. The initial uptake coefficient of NO2 on illuminated TiO2 surface (with 90 ppb of NO2 and JNO2 ≅ 0.006 s−1) was found to be γ0 = (1.2 ± 0.4) × 10−4 (calculated using BET surface area) under dry conditions at T = 300 K. The steady state uptake, γ, was several tens of times lower than the initial one, independent of relative humidity, and was found to decrease in the presence of molecular oxygen. In addition, it was shown that γ is not linearly dependent on the photon flux and seems to level off under atmospheric conditions. Finally, the following expression for γ was derived, γ = 2.3 × 10−3 exp(−1910/T)/(1 + P0.36) (where P is O2 pressure in Torr), and recommended for atmospheric applications (for any RH, near 90 ppb of NO2 and JNO2 = 0.006 s−1). In addition, HONO, NO and N2O were found to be released into the gas phase as a result of the heterogeneous photoreaction of NO2 with TiO2 surface. Detailed study of the yield of these products is the subject of our current work.

Citation: El Zein, A. and Bedjanian, Y.: Interaction of NO2 with TiO2 surface under UV irradiation: measurements of the uptake coefficient, Atmos. Chem. Phys. Discuss., 11, 27861-27885, doi:10.5194/acpd-11-27861-2011, 2011.
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