Interaction process between gaseous CHI and NaCl particles: implication for iodine dispersion in the atmosphere.

Gaseous iodomethane (CHI) is naturally emitted into the atmosphere by biological activity in oceans and during severe accidents (SAs) in nuclear power plants. In this latter case, a part of radioactive iodine such as I may be released. Improving the knowledge of CHI transport and reactivity in the atmosphere is important since they are strongly linked to first the cycle of ozone and second to the dispersion of radioactive CHI with potential radiological consequences on both the environment and human health. Here, the interaction process of CHI with NaCl as a surrogate of atmospheric aerosols was investigated under ambient air conditions by using Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of NaCl clearly evidenced CHI adsorption on the NaCl particle surface. A part of CHI ((1.68 ± 0.85) × 10 molecule per mg) was found to be strongly bonded to NaCl since no desorption was observed. The CHI adsorption on the NaCl surface presented a 1 order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10. These results show a low probability of CHI to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme.