Interaction process between gaseous CH3I and NaCl particles: implication for iodine dispersion in the atmosphere

Gaseous iodomethane (CH 3 I) 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 131 I may be released. Improving the knowledge of CH 3 I 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 CH 3 I with potential radiological consequences on both the environment and human health. Here, the interaction process of CH 3 I 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 CH 3 I adsorption on the NaCl particle surface. A part of CH 3 I ((1.68 ± 0.85) × 10 14 molecule per mg NaCl ) was found to be strongly bonded to NaCl since no desorption was observed. The CH 3 I adsorption on the NaCl surface presented a 1 s order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10 -11 . These results show a low probability of CH 3 I to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme.