Nitric acid-induced surface disordering on ice

Abstract

We examined the interaction of HNO₃ with water ice for partial pressures 2 × 10⁻⁸ Torr to 1 × 10⁻⁵ Torr and at temperatures from 216 to 256 K using (i) the surface-specific technique ellipsometry and (ii) a coated wall flow tube reactor, both coupled with chemical ionization mass spectrometry detection of HNO₃ in the gas phase. Our ellipsometry results show that exposure to HNO₃ induces surface disordering on ice at a range of environmentally relevant temperatures and HNO₃ partial pressures, particularly in the vicinity of the boundary between the ice and the HNO₃·3H₂O phases. The coated wall flow tube studies indicate that the nature of HNO₃ uptake changes from reversible adsorption to a continuous flux of HNO₃ into the bulk in the presence of a disordered interfacial layer. These results have implications for atmospheric chemistry in the upper troposphere and in polar regions.