Atmospheric iodine chemistry from molecular level to 0D/3D simulations: applications to Fukushima nuclear accident

In the case of a hypothetical nuclear accident, fission products are released into the environment. Simulation tools are commonly used to predict the radiological consequences on populations. After the Fukushima accident, significant differences have been observed between measured and modeled concentrations for iodine 131. This can be attributed to the high reactivity of iodine in the atmosphere not considered in the current dispersion crisis tools.

To address this, a new gas-phase mechanism of atmospheric iodine chemistry was developed containing 248 reactions. In parallel, missing thermokinetic data were determined by molecular-scale simulations for iodous and iodic acids. The 0D simulation results showed a partial and rapid transformation of these iodinated gaseous compounds. The influence of several parameters (air quality, quantity and nature of iodine released) was evaluated. For all simulations, iodine is quickly found in the form of iodine oxides and nitroxides or gaseous iodinated organic compounds. The latter may be the cause of iodinated aerosols formation and deposition.

Results from the 3D chemistry-climate model CAM-Chem will be compared to iodine Fukushima deposits measurements. Implications for atmospheric chemistry (air quality and climate) will be discussed.