Ozone decomposition on Saharan dust: an experimental investigation

F. Hanisch (1) , J. N. Crowley (1)

1 MPIC - Max-Planck-Institut für Chemie

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 (g₀ 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 (g_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.

Domaines: Océan, Atmosphère

F. Hanisch, J. N. Crowley. Ozone decomposition on Saharan dust: an experimental investigation. Atmospheric Chemistry and Physics Discussions, 2002, 2 (6), pp.1809-1845. ⟨hal-00300954⟩