A modeling study of iodine chemistry in the marine boundary layer

Gordon McFiggans, John M C Plane, Beverley J. Allan, Lucy J. Carpenter, Hugh Coe, Colin O'Dowd

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    Abstract

    An observationally constrained photochemical box model has been developed to investigate the atmospheric chemistry of iodine in the marine boundary layer, motivated by recent measurements of the iodine monoxide (IO) radical (Allan et al., this issue). Good agreement with the time series of IO measured at a midlatitude coastal station was achieved by using a reaction scheme that included recycling of iodine through marine aerosol. The strong diurnal variation in IO observed in the subtropical Atlantic was satisfactorily modeled by assuming a constant concentration of iodocarbons that photolyzed to produce roughly 1 × 104 iodine atoms cm-3 s-1 at midday. The significance of the occurrence of IO at concentrations of up to 4 parts per trillion in the marine boundary layer was then considered from three angles. First, the iodine-catalyzed destruction of ozone was shown to be of a magnitude similar to that caused by odd-hydrogen photochemistry, with up to 13% of the available ozone destroyed per day in a marine air mass. Second, the enrichment factor of iodine in marine aerosol compared with surface seawater was predicted to increase to values of several thousand, in sensible accord with observations. Most of the enrichment should be due to the accumulation of iodate, although other iodine species may also be present, depending on the rate of aerosol recycling. Third, the denoxification of the marine boundary layer was found to be significantly enhanced as a result of aerosol uptake of IONO2, formed from the recombination of IO with NO2. Copyright 2000 by the American Geophysical Union.
    Original languageEnglish
    Article number1999JD901187
    Pages (from-to)14371-14385
    Number of pages14
    JournalJournal of Geophysical Research: Atmospheres
    Volume105
    Issue number11
    DOIs
    Publication statusPublished - 16 Jun 2000

    Keywords

    • absorption cross-sections
    • dimethyl sulfide
    • methyl-iodide
    • mace head
    • sea-salt
    • nitrate
    • aerosol
    • ozone
    • hydrolysis
    • mechanism

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