EGU2020-990, updated on 10 Jan 2023
EGU General Assembly 2020
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Iodine chemistry in the tropical and remote open ocean marine boundary layer

Swaleha Inamdar1,2, Liselotte Tinel3, Rosie Chance3, Lucy Jane Carpenter3, Sabu Prabhakaran4, Racheal Chacko4, Sarat Chandra Tripathy4, Anvita Ulhas Kerkar4, Alok Kumar Sinha4, Bhaskar Parli Venkateswaran4, Amit Sarkar4,5, Rajdeep Roy6, Tomas Sherwen3,7, Carlos Alberto Cuevas8, Alfonso Saiz-Lopez8, Kirpa Ram2, and Anoop Sharad Mahajan1
Swaleha Inamdar et al.
  • 1Indian Institute of Tropical Meteorology, Centre for Climate Change Research, Pune, 411008, 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

Iodine chemistry plays an essential role in controlling the radiation budget by changing various atmospheric parameters. Iodine in the atmosphere is known to cause depletion of ozone via catalytic reaction cycles. It alters the atmospheric oxidation capacity, and lead to ultrafine particle formation that acts as potential cloud condensation nuclei. The ocean is the primary source of iodine; it enters the atmosphere through fluxes of gaseous reactive iodine species. At the ocean surface, seawater iodide reacts with tropospheric ozone (gas) to form inorganic iodine species in gaseous form. These species namely, hypoiodous acid (HOI) and molecular iodine (I2) quickly photolyse to release reactive iodine (I) in the atmosphere. This process acts as a significant sink for tropospheric ozone contributing to ~16% ozone loss throughout the troposphere. Reactive iodine released in the atmosphere undergoes the formation of iodine monoxide (IO) or higher oxides of iodine (IxOx) via self-recombination reactions. It is known that inorganic iodine fluxes (HOI and I2) contribute to 75% of the detected IO over the Atlantic Ocean. However, we did not observe this from ship-based MAX-DOAS studies between 2014-2017. At present, there are no direct observations of inorganic iodine (HOI; few for I2) and are estimated via empirical methods derived from the interfacial kinetic model by Carpenter et al. in 2013. Based on the kinetic model, estimation of HOI and I2 fluxes depends on three parameters, namely, ozone concentration, surface iodide concentration, and the wind speed. This parameterisation for inorganic fluxes assumes a sea surface temperature (SST) of 293 K and has limiting wind speed conditions. Since the parameterisation conditions assumed SST of 293 K higher uncertainties due to errors in activation energy creeps in the estimation of HOI flux compared to I2 as the flux of HOI is ~20 times greater than that of I2. For three consecutive expeditions in the Indian and Southern Ocean, we detected ~1 pptv of IO in the marine boundary layer. These levels are not explained by the calculated inorganic fluxes by using observed and predicted sea surface iodide concentrations. This method of iodine flux estimation is currently used in all global models, along with the MacDonald et al. 2014 iodide estimation method. Model output using these parameterisations have not been able to match the observed IO levels in the Indian and Southern Ocean region. This discrepancy suggests that the process of efflux of iodine to the atmosphere may not be fully understood, and the current parametrisation does not do justice to the observations. It also highlights that the flux of organic iodine may also play a role in observed IO levels, especially in the Indian Ocean region. A correlation of 0.7 was achieved above the 99% confidence limit for chlorophyll-a with observed IO concentration in this region. There is a need to carry more observations to improve the estimation technique of iodine sea-air flux thus improving model predictions of IO in the atmosphere.

How to cite: Inamdar, S., Tinel, L., Chance, R., Jane Carpenter, L., Prabhakaran, S., Chacko, R., Chandra Tripathy, S., Ulhas Kerkar, A., Kumar Sinha, A., Parli Venkateswaran, B., Sarkar, A., Roy, R., Sherwen, T., Alberto Cuevas, C., Saiz-Lopez, A., Ram, K., and Sharad Mahajan, A.: Iodine chemistry in the tropical and remote open ocean marine boundary layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-990,, 2020.

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