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Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine


Naturally occurring bromine- and iodine-containing compounds substantially reduce regional, and possibly even global, tropospheric ozone levels1,2,3,4. As such, these halogen gases reduce the global warming effects of ozone in the troposphere5, and its capacity to initiate the chemical removal of hydrocarbons such as methane. The majority of halogen-related surface ozone destruction is attributable to iodine chemistry2. So far, organic iodine compounds have been assumed to serve as the main source of oceanic iodine emissions1,6,7,8,9. However, known organic sources of atmospheric iodine cannot account for gas-phase iodine oxide concentrations in the lower troposphere over the tropical oceans3,4. Here, we quantify gaseous emissions of inorganic iodine following the reaction of iodide with ozone in a series of laboratory experiments. We show that the reaction of iodide with ozone leads to the formation of both molecular iodine and hypoiodous acid. Using a kinetic box model of the sea surface layer and a one-dimensional model of the marine boundary layer, we show that the reaction of ozone with iodide on the sea surface could account for around 75% of observed iodine oxide levels over the tropical Atlantic Ocean. According to the sea surface model, hypoiodous acid—not previously considered as an oceanic source of iodine—is emitted at a rate ten-fold higher than that of molecular iodine under ambient conditions.

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Figure 1: Gaseous I2 and HOI emissions from ozonized iodide solutions and sea water as a function of [O3(g)] and [I(aq)].
Figure 2: Schematic of HOI and I2 production following the reaction of O3 with I at the air–sea interface.
Figure 3: Modelled iodine chemistry at Cape Verde using the 1D model THAMO.


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We acknowledge the UK NERC SOLAS (Surface Ocean Lower Atmosphere) programme for funding and would like to thank J. Lee, University of York, for loan of the O3 generator and monitor. M.D.S. and S.M.M. thank the NERC for the award of PhD studentships. S.M.M. would also like to thank Vanessa Cox for assistance with the University of Leeds experiments.

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L.J.C. and J.M.C.P. designed the experiments and S.M.M., M.D.S., R.K. and R.W.S. carried them out. L.J.C. designed and implemented the interfacial model and interpreted the data. R.P. developed some of the aqueous iodine mechanism used in the interfacial model and performed aqueous iodine experiments to validate it. J.M.C.P. carried out the atmospheric modelling. J.W. performed the linear regression modelling. L.J.C. prepared the manuscript, with contributions from all authors.

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Correspondence to Lucy J. Carpenter or John M. C. Plane.

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The authors declare no competing financial interests.

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Carpenter, L., MacDonald, S., Shaw, M. et al. Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine. Nature Geosci 6, 108–111 (2013).

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