[摘要] The heterogeneous reactionSO
2 + H
2O
2 
H
2SO
4 on ice at228 K has been studied in a low temperature coated-wall flow tube.With H
2O
2 in excess ofSO
2, the loss of SO
2 on an ice surface is time dependent with the reaction most efficient on a freshly exposed surface. The deactivation of thesurface arises because the protons formed in the reaction inhibit the dissociation of adsorbedSO
2.This lowers the surface concentrations of HSO
3-, a participant in the rate-determining step of the oxidationmechanism. For a fixed SO
2 partial pressure of 1.4 x 10
-4Pa, the reaction probabilities for SO
2 loss on a freshly exposed surface scale linearly withH
2O
2 partial pressures between 2.7 x 10
-3 and 2.7x 10
-2 Pa because the H
2O
2 surface coverage is unsaturated in this regime. Conversely, the reaction probabilitiesdecrease as the partial pressure of SO
2 is raised from 2.7 x 10
-5 to 1.3x 10
-3 Pa, for a fixed H
2O
2 partial pressure of 8.7x 10
-3 Pa. This is expected if the rate determining step for the mechanism involvesHSO
3- rather than SO
2.It may also arise to some degree if there is competition between gas phaseSO
2 and H
2O
2 for adsorption sites. The reaction is sufficiently fast that the lifetime ofSO
2 within ice clouds could be controlled by this heterogeneous reaction and not by the gas-phase reaction with OH.
