17 Nov 2023
 | 17 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

An improved estimate of inorganic iodine emissions from the ocean using a coupled surface microlayer box model

Ryan J. Pound, Lucy V. Brown, Mat J. Evans, and Lucy J. Carpenter

Abstract. Iodine at the ocean’s surface impacts climate and health by removing ozone (O3) from the troposphere both directly, via ozone deposition to seawater, and indirectly via the formation of iodine gases which are released into the atmosphere. Here we present a new box model of the ocean surface microlayer that couples oceanic O3 dry deposition to inorganic chemistry to predict inorganic iodine emissions. This model builds on the previous work of Carpenter et al. (2013), improving both chemical and physical processes. This new box model predicts iodide depletion in the top few micrometres of the ocean surface, due to rapid chemical loss to ozone competing with replenishment from underlying water. From this box model, we produce parameterised equations for HOI and I2 emissions which are implemented into the global chemical transport model GEOS-Chem. Compared to the previous model, inorganic iodine emissions from tropical waters decrease by as much as half, while higher latitude emissions increase by a factor of ∼10. Despite these large local changes, global total inorganic iodine emissions increased by only ∼ 4 % (2.83 Tg to 2.95 Tg) compared to the previous parameterization. This results in a negligible change in average tropospheric OH (<0.1 %) and tropospheric methane lifetime (<0.1 %). The annual mean tropospheric O3 burden changes negligibly (an increase of 0.2 % to 330 Tg), however, higher latitude surface O3 concentrations decrease by as much as 15 % with equatorial O3 concentrations increasing by up to 10 %.

Ryan J. Pound et al.

Status: open (until 29 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Ryan J. Pound et al.

Ryan J. Pound et al.


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Short summary
Iodine-mediated loss of ozone to the ocean surface and the subsequent emission of iodine species has a large effect on the troposphere. Here we combine recent experimental insights to develop a box model of the process, which we then parameterise and incorporate into the GEOS-Chem transport model. We find that these new insights have a small impact on the total emission of iodine but significantly change its distribution.