Formation of Bromine From Deliquesced NaBr Aerosol in the Presence of

Ozone and UV Light

Bromine plays an important role in ozone destruction in both the upper and lower atmosphere. The formation of gas-phase bromine from aqueous sodium bromide particles under different conditions is investigated using a combination of chamber experiments and chemical kinetics modeling. In all experiments bromine is produced rapidly from deliquesced NaBr particles in the presence of ozone upon illumination by UV light. The mechanisms responsible for the "bromine explosion" are examined using a comprehensive chemical kinetics model. A sensitivity analysis on the model reveals that a complex mechanism involving gas-phase chemistry, aqueous-phase chemistry, and mass transfer are responsible for most of the observed bromine. However, the rate-limiting steps in the bromine explosion pathway vary depending on the system parameters, such as particle size. Interface reactions, an important source of bromine production under dark conditions, account for a small fraction of total bromine produced.