FTIR spectroscopic studies of the simultaneous condensation of HCl and H₂O at 190 K – atmospheric applications

I. Xueref (1) , F. Dominé (1)

1 LGGE - Laboratoire de glaciologie et géophysique de l'environnement

Type II polar stratospheric cloud particles are made up of ice that forms by water vapor condensation in the presence of numerous trace gases, including HCl. These gaseous species can co-condense with water molecules and perturb ice structure and reactivity. In order to investigate the effect of co-condensing dopants on the structure of ice, we have designed an experimental system where ice films can be stabilized at 190 K, a temperature relevant to the polar stratosphere. We have co-condensed different HCl:H₂O gaseous mixtures, with ratios 5:1, 1:10, 1:50 and 1:200 and studied the solids formed by infrared spectroscopy. The IR spectra obtained show that: (1) HCl undergoes ionic dissociation when it is incorporated by co-condensation into the ice at 190 K; (2) this dissociation is done by several water molecules per HCl molecule; and (3) furthermore, HCl and H₂O do not form crystalline HCl hydrates, but rather form non-crystalline solids, that appear homogeneous, and in which HCl is solvated by several water molecules. Considering the major impact of HCl on ice structure observed here, and the well known impact of the structure of solids on their reactivity, we conclude that the actual reactivity of stratospheric ice particles, that catalyze reactions involved in ozone depletion, may be different from what has been measured in laboratory experiments that used pure ice.

Domaines: Océan, Atmosphère

I. Xueref, F. Dominé. FTIR spectroscopic studies of the simultaneous condensation of HCl and H₂O at 190 K – atmospheric applications. Atmospheric Chemistry and Physics Discussions, 2003, 3 (4), pp.4037-4067. ⟨hal-00327869⟩