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Rapid Formation of Molecular Bromine from Deliquesced NaBr Aerosol in the Presence of Ozone and UV Light
Nissenson, P., L. Wingen, S. Hunt, B. Finlayson-Pitts, AND D. Dabdub. Rapid Formation of Molecular Bromine from Deliquesced NaBr Aerosol in the Presence of Ozone and UV Light. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 89:491-506, (2014).
This paper provides a description of combination of chamber experiments and chemical kinetics modeling to invesigate the most important species and reactions leading to the observed bromine explostion. The paper describes how the chamber experiments are related to what occurs in the marine boundary layer. This work informs what chemical kinetics shoud be included in regional air quality models in areas that are impacted by sea salt aerosol or other sources of aqueous sodium bromide solutions.
The formation of gas-phase bromine from aqueous sodium bromide aerosols is investigated through a combination of chamber experiments and chemical kinetics modeling. Experiments show that Br2(g) is produced rapidly from deliquesced NaBr aerosols in the presence of OH radicals produced by ozone irradiated by UV light. The mechanisms responsible for the “bromine explosion” are examined using a comprehensive chemical kinetics Model of Aqueous, Gaseous, and Interfacial Chemistry (MAGIC). A sensitivity analysis on the model confirms that a complex mechanism involving gas-phase chemistry, aqueous-phase chemistry, and mass transfer is responsible for most of the observed bromine. However, the rate-limiting steps in the bromine explosion pathway vary, depending on the availability of ozone and bromide in the system. Interface reactions, an important source of bromine production under dark conditions, account for only a small fraction of total bromine under irradiation. Simulations performed with gaseous ozone and aerosol bromide concentrations typical of the marine boundary layer also show Br2(g) production, with BrO(g) and HOBr(g) as the dominant Br-containing products through this mechanism. Aerosol bromide is depleted after several hours of daylight, with photolysis of BrO(g) and HOBr(g) becoming major sources of Br atoms that continue generating Br2(g) after aerosol bromide is depleted.