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Ozone decomposition on Saharan dust: an experimental investigation

by F. Hanisch, J. N. Crowley
Atmospheric Chemistry and Physics Discussions ()

Abstract

The heterogeneous reaction between O-3 and authentic Saharan dust\nsurfaces was investigated in a Knudsen reactor at; approximate to296\nK. O-3 was destroyed on the dust surface and O-2 was formed with\nconversion efficiencies of 1.0 and 1.3 molecules O-2 per O-3 molecule\ndestroyed for unheated and heated samples, respectively. No O-3 desorbed\nfrom exposed dust samples, showing that the uptake was irreversible.\nThe uptake coefficients for the irreversible destruction of O-3 on\n(unheated) Saharan dust surfaces depended on the O-3 concentration\nand varied between 15 X 10(-4) and 5.5 x 10 6 for the initial uptake\ncoefficient (gamma(0) approximate to 3 x 10(-5) at 30 ppbv O-3 {STP)}\nand between 4.8 x 10(-5) and 2.2 x 10(-6) for the steady-state uptake\ncoefficient {(gamma(SS)} approximate to 7 x 10(-6) at 30 ppbv O-3\n{STP).} At very high O-3 concentrations the surface was deactivated,\nand O-3 uptake ceased after a certain exposure period. Sample re-activation\n(i.e. de-passivation) was found to occur over periods of hours, after\nexposure to O-3 had ceased, suggesting that re-activation processes\nplay a role both in the laboratory and in the atmosphere.

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