Inorganic iodine speciation in tropical Atlantic aerosol

The inorganic speciation of soluble iodine has been determined in size-fractionated aerosol samples collected from the tropical Atlantic Ocean in October/November 2002 during Meteor cruise 55, a pilot study of the German SOLAS programme. Iodide concentrations were appreciable (>0.4 pmol m−3) in the fine and coarse modes of all samples whereas iodate was occasionally below detection limit (∼0.7 pmol m−3) in samples from northern hemisphere air and was undetectable in all samples from the southern hemisphere. Iodine was enriched, and chlorine and bromine depleted, relative to seasalt concentrations. The majority of Cl− loss was due to the seasalt displacement reaction. Halogen activation (I− + HOX + H+ = IX + H2O) may also have occurred, but did not result in net I− depletion in any aerosol fraction. The observed variations of iodine speciation cannot be reproduced by current models of aerosol iodine chemistry.