Preprints
https://doi.org/10.5194/acp-2021-72
https://doi.org/10.5194/acp-2021-72

  26 Apr 2021

26 Apr 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Measurement report: Indirect evidence for the controlling influence of acidity on the speciation of iodine in Atlantic aerosols

Alex R. Baker1 and Chan Yodle1,a Alex R. Baker and Chan Yodle
  • 1Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, U.K.
  • anow at: Department of Environmental Science, Faculty of Science and Technology, Chiang Mai Rajabhat University, Chiang Mai, Thailand 50300

Abstract. The speciation of iodine and major ion composition were determined in size-fractionated aerosols collected during the AMT21 cruise between Avonmouth, UK and Punta Arenas, Chile in September–November 2011. The proportions of iodine species (iodide, iodate and soluble organic iodine (SOI)) varied markedly between size fractions and with the extent to which the samples were influenced by pollutants. In general, fine mode aerosols (< 1 µm) contained higher proportions of both iodide and SOI, while iodate was the dominant component of coarse (< 1 µm) aerosols. The highest proportions of iodate were observed in aerosols that contained (alkaline) unpolluted seaspray or mineral dust. Fine mode samples with high concentrations of acidic species (e.g. non-seasalt sulfate) contained very little iodate and elevated proportions of iodide and SOI. These results are in agreement with modelling studies that indicate that iodate can be reduced under acidic conditions and that the resulting hypoiodous acid (HOI) can react with organic matter to produce SOI and iodide. Further work that investigates the link between iodine speciation and aerosol pH directly, as well as studies on the formation and decay of organo-iodine compounds under aerosol conditions, will be necessary before the importance of this chemistry in regulating aerosol iodine speciation can be confirmed.

Alex R. Baker and Chan Yodle

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-72', Anonymous Referee #1, 02 May 2021
  • RC2: 'Comment on acp-2021-72', Anonymous Referee #2, 15 Jun 2021

Alex R. Baker and Chan Yodle

Alex R. Baker and Chan Yodle

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Short summary
Iodine is emitted from the ocean and helps to destroy ozone in the lower atmosphere before being taken up into aerosol particles. We measured the chemical forms of iodine in aerosols over the Atlantic Ocean because some of these forms can return to the gas phase and destroy more ozone. Our results indicate that aerosol acidity exerts a strong control on iodine speciation and therefore on its recycling behaviour and impact on ozone concentrations.
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