Interaction of NO<sub>2</sub> with TiO<sub>2</sub> surface under UV irradiation: measurements of the uptake coefficient

Abstract

Abstract. The interaction of NO 2 with TiO 2 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 NO 2 to TiO 2 reactive uptake coefficient was measured from the kinetics of NO 2 loss on TiO 2 coated Pyrex rods as a function of NO 2 concentration, irradiance intensity (J NO 2 = 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). TiO 2 surface deactivation upon exposure to NO 2 was observed. The initial uptake coefficient of NO 2 on illuminated TiO 2 surface (with 90 ppb of NO 2 and J NO 2 ∼ =0.006 s −1 ) was found to be γ 0 = (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 + P 0.36 ) (where P is O 2 pressure in Torr), and recommended for atmospheric applications (for any RH, near 90 ppb of NO 2 and J NO 2 = 0.006 s −1 ).

Temperature dependencies of the degradation of NO, NO2 and HONO on a photocatalytic dispersion paint

“…25 In contrast, for the same catalyst (P25) an increasing uptake of NO 2 and decreasing HONO yields were observed with increasing temperature in a low pressure flow tube under dry conditions (buffer gas He). 28,29 A qualitatively similar temperature dependence of the NO 2 uptake was observed on an indoor photocatalytic paint, while the HONO yields were found to increase with temperature in this environmentally more realistic study. 30 However, the absolute water vapor pressure was kept constant, leading to decreasing relative humidity on the surface with increasing surface temperature.…”

Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with airborne TiO<sub>2</sub> particles and its implication for stratospheric particle injection

“…Additionally, the potential photocatalytic activity of TiO 2 is likely to play a role. For example, the uptake of NO 2 on TiO 2 particles is enhanced under irradiation (Gustafsson et al, 2006;Ndour et al, 2008;El Zein and Bedjanian, 2012), leading to the formation of HONO, the photolysis of which produces NO and OH and may perturb the stratospheric NO x and HO x cycles. Heterogeneous chemical oxidation of SO 2 could enhance the formation of sulfate coating on mineral particles (Shang et al, 2010).…”

Uptake of HO<sub>2</sub> radicals on Arizona Test Dust

“…The experimental equipment and approach used for the kinetic measurements have been described in previous papers from this group (Bedjanian et al, 2005;Loukhovitskaya et al, 2009;El Zein and Bedjanian, 2012). The main reactor (Fig.…”