Multiphase Halogen Chemistry
in the Tropical Atlantic
Ocean
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Abstract
We used a one-dimensional model to simulate the chemical
evolution
of air masses in the tropical Atlantic Ocean, with a focus on halogen
chemistry. The model results were compared to the observations of
inorganic halogen species made in this region. The model could largely
reproduce the measurements of most chlorine species, especially under
unpolluted conditions, but overestimated sea salt chloride, BrCl,
and bromine species. Agreement with the measurements could be improved
by taking into account the reactivity with aldehydes and the effects
of dimethyl sulfide (DMS) and Saharan dust on aerosol pH; a hypothetical
HOX → X<sup>–</sup> aqueous-phase reaction could also
improve the agreement with measured Cl<sub>2</sub> and HOCl, especially
under semipolluted conditions. The results also showed that halogens
speciation and concentrations are very sensitive to cloud processing.
The model was used to calculate the impact of the observed levels
of halogens: Cl atoms accounted for 5.4–11.6% of total methane
sinks and halogens (mostly bromine and iodine) accounted for 35–40%
of total ozone destruction