Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 2 6 2002 10.5194/acpd-2-1809-2002 http://www.atmos-chem-phys-discuss.net/2/1809/2002/ http://www.atmos-chem-phys-discuss.net/2/1809/2002/acpd-2-1809-2002.html http://www.atmos-chem-phys-discuss.net/2/1809/2002/acpd-2-1809-2002.pdf 1809 1845 2002-11-05 Ozone decomposition on Saharan dust: an experimental investigation F. Hanisch J. N. Crowley Max-Planck-Institut für Chemie, Division of Atmospheric Chemistry, Postfach 3060, 55020 Mainz, Germany The heterogeneous reaction between O₃ and authentic Saharan dust surfaces was investigated in a Knudsen reactor at approx 296 K. O₃ was destroyed on the dust surface and O₂ was formed with conversion efficiencies of 1.0 and 1.3 molecules O₂ per O₃ molecule destroyed for unheated and heated samples, respectively. No O₃ desorbed from exposed dust samples, showing that the uptake was irreversible. The uptake coefficients for the irreversible destruction of O₃ on (unheated) Saharan dust surfaces depended on the O₃ concentration and varied between 3.5 x10^-4 and 5.5 x10^-6 for the initial uptake coefficient (<font face="Symbol" >g</font>₀ approx 3 x10^-5 at 30 ppbv O₃ STP) and between 4.8 x10^-5 and 2.2 x10^-6 for the steady-state uptake coefficient (<font face="Symbol" >g</font>_ss approx 7 x10^-6 at 30 ppbv O₃ STP). At very high O₃ concentrations the surface was deactivated, and O₃ uptake ceased after a certain exposure period. Sample re-activation (i.e. de-passivation) was found to occur over periods of hours, after exposure to O₃ had ceased, suggesting that re-activation processes play a role both in the laboratory and in the atmosphere.