A modeling study of iodine chemistry in the marine boundary layer

Abstract

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 x 10 4 iodine atoms cm '3 s -• 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.

Injection of iodine to the stratosphere

“…However, the heterogeneous recycling of iodine species on ice particles remains unexplored [Saiz-Lopez et al, 2012a], and therefore, two different sets of simulations have been performed to account for the impact of heterogeneous uptake: the ice-recycling and non-recycling schemes of the main iodine reservoir species, hypoiodous acid (HOI), and iodine nitrate (IONO 2 ). The recycling reactions rates were computed by means of the free regime approximation [McFiggans et al, 2000], which considers that the Figure 1. Atmospheric chemistry of iodine.…”

Marine aerosol production: a review of the current knowledge

“…Sea spray not only affects climate by scattering of solar radiation, but also the spray particles act as cloud condensation nuclei and thus contribute to the indirect aerosol effect (O'Dowd et al 1999b). Sea salt has also been linked to the MBL cycle through the activation of halogens, leading to ozone depletion (Vogt et al 1996;McFiggens et al 2000). For primary marine aerosol (PMA), a historical and detailed review of sea-salt production and resulting concentrations is discussed in Lewis & Schwartz (2005).…”

Marine organohalogens in the atmosphere over the Atlantic and Southern Oceans

“…Active RHS chemistry has so far been demonstrated in regions including the Arctic and Antarctica, where abrupt bromine oxide (BrO) ''episodes'' completely destroy surface ozone on timescales of hours to days [Barrie et al, 1988;Bottenheim et al, 1990;Tuckermann et al, 1997]; coastal areas, where concentrations of the IO radical can be sufficiently high to double the marine boundary layer (MBL) depletion rate of O 3 McFiggans et al, 2000]; and the Dead Sea valley, where the highest tropospheric BrO concentrations to date have been observed . Recently, another important role for RHS has been proposed.…”