The features of haloacetic acid oxidation that contribute to stratospheric ozone depletion

Abstract

Environmental context Due to The Montreal Protocol, stratospheric ozone concentration is slowly regenerating, however, the recovery rate is slower than predicted by photochemical models. FTIR spectroscopy together with quantum chemical calculations confirmed that ozone reacts with halogenated acids adsorbed at a model aerosol surface. Reactions occur at low temperatures without photochemical activation with formation of halogen oxides that are known to promote catalytic cycles of ozone depletion. Abstract The present work addresses the problem of stratospheric ozone depletion. While gas phase and photochemically induced reactions of ozone are well studied, the mechanisms of heterogeneous O3 interactions with different halogenated species still remain uncertain. An in situ FTIR investigation of low-temperature heterogeneous reactions of ozone and haloacetic acids in conditions close to stratospheric was performed and supported by ab initio quantum chemical calculations. Products of ozone reaction with differently chlorine and bromine-substituted acetic acids were identified and possible reactions pathways were suggested. Ozone can attach to a carbon atom to release a halogen atom that forms a halogen oxide. Halogen oxide in its turn can take part in the catalytic cycles of ozone depletion. Suggested reaction pathways leading to the additional release of the chlorine oxides can enhance the atmospheric models that calculate ozone concentration.