INTRODUCTION

The understanding of the chlorine chemistry of the lower stratosphere has strongly increased since the discovery of the so called ozone hole of the Antarctic. The actual picture of the chemistry in this region involves two phases and steps1:

a) During the polar night reactions on the surface of polar stratospheric clouds (PSCs) lead to chlorine activation:

ClONO2(g) + HCl(s) ¾® Cl2(g) + HNO3(s)

ClONO2(g) + H2O(s) ¾® HOCl(g) + HNO3(s)

HOCl(g) + HCl(s) ¾® Cl2(g) + H2O(s)

b) In currently accepted homogenous chemistry, chlorine destroys polar ozone primarily through the ClO dimer catalytic cycle which requires sunlight to proceed. The rate of dimer formation limits the destruction rate of ozone under typical conditions found in the Antarctica springtime lower stratosphere. In spite of the intensive research carried out on the steps (a) and (b) there are few studies which take into account processes involving heterogeneous photochemistry2. Chlorine nitrate plays an important role in both the activation and deactivation of chlorine. In addition, the kinetic of the uptake of ClONO2 on ice dramatically depends on the surface compositions.

We started and present here the heterogeneous photochemistry of this reservoir species, ClONO2, adsorbed on ice at stratospheric temperatures, to examine the implications of this kind of processes in the chemistry of the lower polar stratosphere.

INTRODUCTION EXPERIMENTAL RESULTS DISCUSSION ATMOSPHERIC IMPLICATIONS REFERENCES