The interaction of H2O2 with ice surfaces between 203 and 233 K

Abstract

The interaction of H₂O₂ with ice surfaces at temperatures between 203 and 233 K was investigated using a low pressure, coated-wall flow tube equipped with a chemical ionisation/electron impact mass spectrometer. Equilibrium surface coverages of H₂O₂ on ice were measured at various concentrations and temperatures to derive Langmuir-type adsorption isotherms. H₂O₂ was found to be strongly partitioned to the ice surface at low temperatures, with a partition coefficient, K_linC, equal to 2.1 × 10⁻⁵ exp(3800/T) cm. At 228 K, this expression results in values of K_linC which are orders of magnitude larger than the single previous determination and suggests that H₂O₂ may be significantly partitioned to the ice phase in cirrus clouds. The partition coefficient for H₂O₂ was compared to several other trace gases which hydrogen-bond to ice surfaces and a good correlation with the free energy of condensation found. For this class of trace gas a simple parameterisation for calculating K_linC(T) from thermodynamic properties was established.