ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-1301-2004 Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles Sullivan R. C. 1 2 Thornberry T. 1 3 Abbatt J. P. D. 1 Department of Chemistry, University of Toronto, 80 St. George St., Toronto, ON, Canada present address: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA present address: Aeronomy Lab, NOAA, Boulder, CO, USA 23 08 2004 4 5 1301 1310 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/1301/2004/acp-4-1301-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/1301/2004/acp-4-1301-2004.pdf

The room temperature kinetics of gas-phase ozone loss via heterogeneous interactions with thin alumina films has been studied in real-time using 254nm 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 77K. 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 1.4x10<sup>14</sup> active sites per cm<sup>2</sup> 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<sup>-6</sup> for ozone concentrations of 10<sup>14</sup> molecules/cm<sup>3</sup> to 10<sup>-5</sup> at 10<sup>13</sup> molecules/cm<sup>3</sup>. 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.