Global budget of atmospheric 129I during 2007–2010 estimated by a chemical transport model: GEARN–FDM

Abstract

The behaviors of atmospheric 129 I and the global 129 I cycle 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 129 I budget. When quantifying, we conducted global atmospheric 129 I dispersion simulations covering from the period 2007 to 2010. To achieve this goal, the present study newly incorporates the iodine chemical processes of two gas-phase chemical reactions, six photolysis reactions, and two heterogeneous reactions into an existing atmospheric 129 I transport model (GEARN–FDM). In addition to the aerial release of 129 I from nuclear fuel reprocessing facilities, the model includes the volatilization processes of 129 I compounds from the Earth’s surface. The net 129 I exchange fluxes from the atmosphere to the Earth’s oceans and land were estimated to be 5.3 GBq/y and 18.0 GBq/y, respectively. The global 129 I emission from the oceans was estimated as 7.2 GBq/y, and nearly half of the emission totals are emitted from the English Channel (3.2 GBq/y). In addition, the global 129 I emissions from land are estimated to be 1.7 GBq/y. The remarkable 129 I emission levels from land mainly appear in Europe, Russia, and North America, and the emission distribution is impacted by the activities of past and ongoing nuclear fuel reprocessing facilities. The total 129 I emissions from the oceans and land are lower than the 129 I emissions from the model-included nuclear fuel reprocessing facilities (23.3 GBq/y), and show that the aerial releases from the nuclear fuel reprocessing facilities in operation are still important 129 I sources. • Heterogeneous, photolysis, and gas-phase reactions were implemented in GEARN–FDM. • GEARN–FDM captured the 129 I concentrations in rainfall in the Northern Hemisphere. • Aerial discharges from reprocessing facilities greatly impacts the 129 I budget. • Emissions from the English Channel are the largest oceanic source of 129 I. • Terrestrial emissions locally dominate 129 I deposition in North America.