Global budget of atmospheric I during 2007-2010 estimated by a chemical transport model: GEARN-FDM

Kadowaki, Masanao   ; Terada, Hiroaki   ; Nagai, Haruyasu  

The behaviors of atmospheric I and the global cycle of I remain incompletely understood because the spatiotemporal resolution of monitoring is insufficient and few measurement-based models have been reported. This study aims to quantitatively understand the global budget of I. When quantifying, we conduct global atmospheric I dispersion simulations covering from 2007 to 2010. To achieve this goal, the present study newly incorporated the iodine chemistry processes of two gas-phase chemical reactions, six photolysis reactions, and two heterogeneous reactions into an existing atmospheric I transport model (GEARN-FDM). Besides the aerial release of I from nuclear fuel reprocessing facilities, the model includes the volatilization processes of I compounds from Earth's surface. The net I exchange fluxes from the atmosphere to the Earth's surface of land and ocean were estimated as 18.0 GBq/y and 5.3 GBq/y, respectively. The global I emission from oceans was estimated as 7.2 GBq/y, nearly half of the emission totals were emitted from the English Channel (3.2 GBq/y). In addition, the global I emission from land was estimated as 1.7 GBq/y. The remarkable I emission from land was mainly appeared in Europe, Russia, and North America, and the emission distribution is impacted by the activities of the past and ongoing nuclear fuel reprocessing facilities. The total I emission from ocean and land is lower than the I emission from the model-included nuclear fuel reprocessing facilities (23.3 GBq/y), showing that the aerial release of nuclear fuel reprocessing facilities in operation is still an important I source.