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

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, KlinC, equal to 2.1 × 10−5 exp(3800/T) cm. At 228 K, this expression results in values of KlinC 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 KlinC(T) from thermodynamic properties was established.