Production of Molecular Iodine via a Redox Reaction between Iodate and Organic Compounds in Ice.

The abiotic mechanism of molecular iodine (I) production from iodate (IO) remains largely unknown. Here, we demonstrate the production of I in the presence of IO and organic compounds in ice. When the solution containing IO (100 μM) and furfuryl alcohol (100 μM) at pH 3.0 was frozen at -20 °C, 13.1 μM of I was produced with complete degradation of furfuryl alcohol after 20 min. However, there was little change in the IO and furfuryl alcohol concentrations in water at 25 °C. The production of I in ice is due to the freeze concentration effect, which induces the accumulation of IO, furfuryl alcohol, and protons in the ice grain boundaries. This behavior facilitated the production of I via a redox reaction between IO and organic compounds. The production of I increased with increasing furfuryl alcohol concentration and decreasing pH. However, freezing temperature had a minor effect on the maximum production of I. The production of I is highly dependent on the type of organic compounds. It was higher for organic compounds with higher electron-donating properties. This study suggests a new mechanism for I production, which is helpful for predicting precisely the atmospheric I budget in cold regions.