SEGH Articles

Modeling global Iodine in Global Atmosphere and its Deposition

08 September 2014
Tomas Sherwen is an Atmospheric Chemistry PhD Student and won the SEGH 2014 student prize for best poster.


Iodine is a crucial element for human health. Iodine deficiency in both developing and developed nations is implicated in multiple developmental conditions. The iodine in the food chain originates from the ocean where it is emitted into the atmosphere as either organic (e.g. CH3I, CH2IX) or inorganic (e.g. I2, HOI) compounds. To understand the global environmental distribution of we need to bring together knowledge of the emissions and interactions in the atmosphere that transform and transport iodine and lead to eventual deposition. There are significant uncertainties of atmospheric processing and uptake into the biosphere, but recent and continuing work has providing new insight into the sources iodine and their processing within the global atmosphere. Our work aims to bring together this understanding of atmospheric iodine within a global atmospheric chemistry – transport model, enabling evaluation including spatial understanding that can enable estimation of iodine deposition.

As a PhD student in atmospheric chemistry I am interested in understanding the impacts and interactions of the chemistry of iodine on our atmosphere from its sources in the ocean to its deposition to either the ocean or land surface, and everything in between. The emitted iodine containing compounds are quickly broken down by sunlight to form reaction iodine compounds (I, IO) which undergo further reactions with chemicals compounds in the air. Some of these reactions catalytically destroy ozone, which is key atmospheric oxidant and climate gas, whilst others can impact the concentration of methane (another climate gas). By combining our knowledge of these emissions with our understanding of the atmospheric chemistry and physics that process these species in the atmosphere we can model the resultant transport of iodine and it deposition to the land.

Our iodine simulations are implemented into a community chemical transport model (GEOS-Chem, This approach splits the world in boxes, vertically and horizontally, integrating the changes due to chemical reaction and physical processes (dry & wet deposition, photolysis, heterogeneous reactions, etc ) over time. The chemical species are then transported between the boxes via metrology derived from observations. Thus we can compare observation of iodine compounds with predictions from our model. We can then answer quantitative questions about the global iodine system, pulling together experimental knowledge together with our theoretical understanding of chemistry and physics. Through simulations, uncertainties and their impacts can be explored, helping to highlight future research directions.

The ability to understand Iodine from oceanic emission through to photochemical transformations and atmospheric deposition, allows for an estimation of depositional iodine fluxes and comparison with previous approaches. To develop this understanding to estimate resultant bioavailable iodine from these depositional fluxes will require further work considering terrestrial and ecological processing.

by Tomas Sherwen, PhD student

Wolfson Atmospheric Chemistry Laboratories (WACL)

Department of Chemistry

University of York


Further information can be found:

Saiz-Lopez, A., et al., Atmospheric Chemistry of Iodine. Chemical Reviews, 2012. 112(3): p. 1773-1804.

Carpenter, L.J., et al., Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine. Nature Geosci, 2013. 6(2): p. 108-111. 

Chance, R., et al., The distribution of iodide at the sea surface. Environmental Science: Processes & Impacts, 2014. 16(8): p. 1841-1859.

The International Council for the Control of Iodine Deficiency Disorders (ICCIDD) -

GEOS-Chem -