Reactive uptake of ozone on mineral oxides and mineral dusts

A Knudsen cell apparatus was used to measure the heterogeneous reactive uptake of ozone on mineral oxide powders at 296 K. Commercially available powders including alpha-Al(2)O(3), alpha-Fe(2)O(3), SiO(2) and kaolinite were investigated as well as two different authentic mineral dusts, China loess and Saharan sand. Initial reactive uptake coefficients, gamma(o.BET), for the purchased powders were measured as 1.2+/-0.4 x 10(-4) for alpha-Al(2)O(3), 2.0+/-0.3 x 10(-4) for alpha-Fe(2)O(3), 6.3+/-0.9 x 10(-5) for SiO(2) and 3+/-1 X 10(-5) for kaolinite. Authentic dust samples were found to have gamma(oBET) values of 2.7+/-0.8 x 10(-5) for China loess and 6+/-2 x 10(-5) for ground Saharan sand. Pressure dependence studies of this reaction on alpha-Al(2)O(3) and alpha-Fe(2)O(3) suggest that the initial uptake of ozone on these mineral oxides is a first-order process. Furthermore, under conditions of this study, these powders exhibit catalytic behavior toward the decomposition of ozone, and have turnover rates greater than one. Additionally, the reactive uptake of ozone on alpha-Al(2)O(3) showed a small temperature dependence over a range of temperatures from 250 to 330 K, consistent with reports of low energies of activation (similar to5-10 kJ mol(-1)) for ozone destruction on oxide powders. (C) 2003 Elsevier Science Ltd. All rights reserved.