The abiotic mechanism of molecular iodine (I 2 ) production from iodate (IO 3 − ) remains largely unknown. Here, we demonstrate the production of I 2 in the presence of IO 3 − and organic compounds in ice. When the solution containing IO 3 − (100 μM) and furfuryl alcohol (100 μM) at pH 3.0 was frozen at −20 °C, 13.1 μM of I 2 was produced with complete degradation of furfuryl alcohol after 20 min. However, there was little change in the IO 3 − and furfuryl alcohol concentrations in water at 25 °C. The production of I 2 in ice is due to the freeze concentration effect, which induces the accumulation of IO 3 − , furfuryl alcohol, and protons in the ice grain boundaries. This behavior facilitated the production of I 2 via a redox reaction between IO 3 − and organic compounds. The production of I 2 increased with increasing furfuryl alcohol concentration and decreasing pH. However, freezing temperature had a minor effect on the maximum production of I 2 . The production of I 2 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 2 production, which is helpful for predicting precisely the atmospheric I 2 budget in cold regions.

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