ln field kinetic experiments to better understand chemical mechanisms involved during mercury depletion events (MDE): Preliminary results

In order to better understand MDE chemistry, which are thought to happen in the presence of halogenated (chloride and bromide) species, we have led several kinetic experiments with gaseous mercury, ozone and chlorine in Teflon bags under polar atmospheric conditions. The chlorine was expected to produce, with natural solar radiation, the reactive chloride species assumed to play a role in the MDE mechanism. The aim of the first experiment was to study the reactivity between ozone and gaseous mercury: we obtained a rate constant of (13±6)x10 -20 cm 3 /molec/s, which is roughly comparable to constants given in the literature. Concerning the second experiment, for which chlorine has been introduced, a rate constant of (6.2 ±2.2))x10 -17 cm 3 /molec/s for the reactivity of gaseous mercury was obtained. This constant is too weak to recover the atmospheric lifetime of gaseous mercury during MDE. This difference is in discussion in this paper.