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Preprints
https://doi.org/10.5194/acp-2019-1052
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1052
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  04 Feb 2020

04 Feb 2020

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A revised version of this preprint is currently under review for the journal ACP.

Estimation of Reactive Inorganic Iodine Fluxes in the Indian and Southern Ocean Marine Boundary Layer

Swaleha Inamdar1,2, Liselotte Tinel3, Rosie Chance3, Lucy J. Carpenter3, Prabhakaran Sabu4, Racheal Chacko4, Sarat C. Tripathy4, Anvita U. Kerkar4, Alok K. Sinha4, Parli Venkateswaran Bhaskar4, Amit Sarkar4,5, Rajdeep Roy6, Tomas Sherwen3,7, Carlos Cuevas8, Alfonso Saiz-Lopez8, Kirpa Ram2, and Anoop S. Mahajan1 Swaleha Inamdar et al.
  • 1Centre for Climate Change Research, Indian Institute of Tropical Meteorology, Dr Homi Bhabha Road, Pashan, Pune, 411 008, India
  • 2Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, 221 005, India
  • 3Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, YO10 5DD, UK
  • 4National Centre for Polar and Ocean Research, Goa, 403 804, India
  • 5Environment and Life Sciences Research Centre, Kuwait Institute for Scientific Research Centre, Al-Jaheth Street, Shuwaikh, 13109, Kuwait
  • 6National Remote Sensing Centre, Department of Space Government of India Balanagar, Hyderabad, 500 037, India
  • 7National Centre for Atmospheric Science, University of York, York YO10 5DD, UK
  • 8Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, CSIC, Madrid, Spain

Abstract. Iodine chemistry has noteworthysignificant impacts on the oxidising capacity of the marine boundary layer (MBL) through the depletion of ozone (O3) and changes to HOx (OH/HO2) and NOx (NO/NO2) ratios. Hitherto, studies have shown that the reaction of atmospheric O3 with surface seawater iodide (I) contributes to the flux of iodine species into the MBL mainly as hypoiodous acid (HOI) and molecular iodine (I2). Here, we present the first concomitant observations of iodine oxide (IO), O3 in the gas phase, and sea surface iodide concentrations. The results from three field campaigns in the Indian Ocean and the Southern Ocean during 2014–2017 are used to compute reactive iodine fluxes to the MBL. Observations of atmospheric IO by MAX-DOAS show active iodine chemistry in this environment, with IO values up to 1 pptv (parts per trillion by volume) below latitudes of 40° S. In order to compute the sea-to-air iodine flux supporting this chemistry, we compare previously established global sea surface iodide parameterisations with new, region-specific parameterisations based on the new iodide observations. This study shows that regional changes in salinity and sea surface temperature play a role in surface seawater iodide estimation. Sea-air fluxes of HOI and I2, calculated from the atmospheric ozone and seawater iodide concentrations (observed and predicted), failed to adequately explain the detected IO in this region. This discrepancy highlights the need to measure direct fluxes of inorganic and organic iodine species in the marine environment. Amongst other potential drivers of reactive iodine chemistry investigated, chlorophyll-a showed a significant correlation with atmospheric IO (R = 0.7 above the 99 % significance level) to the north of the polar front. This correlation might be indicative of a biogenic control on iodine sources in this region.

Swaleha Inamdar et al.

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Swaleha Inamdar et al.

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Short summary
Iodine chemistry is generating a lot of interest because of its impacts on the oxidising capacity of the marine boundary and depletion of ozone. However one of the challenges has been predicting the right levels of iodine in the models, which depend on parameterisations for the emissions from the sea surface. This paper discusses the different parameterisations available and compares it with observations, showing that our current knowledge is still insufficient, especially on a regional scale.
Iodine chemistry is generating a lot of interest because of its impacts on the oxidising...
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