Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles

Abstract

Abstract. The room temperature kinetics of gas-phase ozone loss via heterogeneous interactions with thin alumina films has been studied in real-time using 254 nm absorption spectroscopy to monitor ozone concentrations. The films were prepared from dispersions of fine alumina powder in methanol and their surface areas were determined by an in situ procedure using adsorption of krypton at 77 K. The alumina was found to lose reactivity with increasing ozone exposure. However, some of the lost reactivity could be recovered over timescales of days in an environment free of water, ozone and carbon dioxide. From multiple exposures of ozone to the same film, it was found that the number of active sites is large, greater than 1.4×10 14 active sites per cm 2 of surface area or comparable to the total number of surface sites. The films maintain some reactivity at this point, which is consistent with there being some degree of active site regeneration during the experiment and with ozone loss being catalytic to some degree. The initial uptake coefficients on fresh films were found to be inversely dependent on the ozone concentration, varying from roughly 10 −6 for ozone concentrations of 10 14 molecules/cm 3 to 10 −5 at 10 13 molecules/cm 3 . The initial uptake coefficients were not dependent on the relative humidity, up to 75%, within the precision of the experiment. The reaction mechanism is discussed, as well as the implications these results have for assessing the effect of mineral dust on atmospheric oxidant levels.

Geocatalytic Uptake of Ozone onto Natural Mineral Dust

“…The profile can be modeled using a power function, as reported in Equation (6), revealing a fractional reaction order of 0.5 regarding the catalytic decomposition process of ozone onto Gobi dust. The dependence of uptake coefficients on ozone initial concentration can be described by an analytical fit of power functions reported by solid lines in Figure 2 and is given by Equation (3) Similar dependence patterns for γ0 and γss on O have been reported for other materials, such as Al2O3 [11,34]. Since uptake coefficients depict the probability for a molecule to be taken up by a surface when striking it, the decreasing trends in Figure 2 suggest a finite ability of the sample surface to decompose ozone in terms of molecules processed per time and surface unit.…”

“…The dependence of uptake coefficients on ozone initial concentration can be described by an analytical fit of power functions reported by solid lines in Figure 2 and is given by Equation (3) and Equation (4 [11,34]. Since uptake coefficients depict the probability for a molecule to be taken up by a surface when striking it, the decreasing trends in Figure 2 suggest a finite ability of the sample surface to decompose ozone in terms of molecules processed per time and surface unit.…”

“…These massive emissions are mostly related to sandstorms in desert areas and volcanic eruptions. Interestingly, natural mineral dust participates directly in atmospheric activities and significantly interacts with ozone [11,[24][25][26]. In spite of the fact that geochemists introduced the concept of geocatalysis in the 1990s, referring to possible catalytic properties of Earth crustal materials, such catalytic potential has not been experimentally evidenced so far [27].…”

“…Due to environmental concerns and the widespread applications of ozone-based remediation techniques, over the last two decades, the interactions of ozone with metal oxides, such as Al 2 O 3 [7][8][9][10][11], MnO 2 [12,13], Fe 2 O 3 [7,14], SiO 2 [15,16], CaO [17], TiO 2 [18], and MgO [19], have been extensively studied. Most of the investigated synthetic oxides exhibit decomposition properties towards ozone.…”

Chemical Kinetics and Reaction Mechanisms in Solvent Extraction: New Trends and Applications

“…99 Modeling the kinetics of the processes that represent a biophysical system has long been pursued with the aim of improving our understanding of the studied system. Due to the unique properties of biological systems, in addition to the usual difficulties faced in modeling the dynamics of physical or chemical systems, biological simulations encounter difficulties that result from intrinsic multiscale and stochastic nature of the biological processes.…”