Model results show that previously unconsidered iodine chemistry can significantly impact ozone loss at the lower edge of the Antarctic stratospheric ozone hole. Iodine also increases the ozone hole area and mass deficit.

While the role of chlorine and bromine in Antarctic stratospheric ozone depletion is well established, the contribution of ocean-emitted iodine to ozone hole chemistry had not been evaluated, due to the negligible iodine levels previously thought to reach the stratosphere. However, recent aircraft observations have shown that 0.77 pptv of total inorganic iodine enters the stratosphere via tropical convective outflow. Based on these new measurements, we use the WACCM model to assess the overall influence of iodine on the Antarctic ozone hole in the 1980-2015 period.   The results show that iodine chemistry can enhance spring ozone loss at the lower edge of the Antarctic ozone hole (on average 10% in the lower stratosphere), and up to 4% for the total stratosphere over Antarctica. Despite being present in much smaller amounts, and due to faster gas-phase photochemical reactivation, iodine can dominate (~65%) the halogen-mediated ozone loss during summer, when the heterogeneous reactivation of inorganic chlorine and bromine reservoirs is reduced. The inclusion of iodine advances the beginning and delays the closure stages of the ozone hole seasonal cycle by 3-5 days, and increases the ozone hole area and mass deficit by 11% and 20%, respectively. Finally, the role of iodine in Antarctic ozone loss can be almost equivalent to that of the approx. 5 pptv of biogenic very short-lived bromocarbons currently entering the stratosphere.   These results show that iodine injection and chemistry need to be considered in models, along with chlorine and bromine, for accurate assessments and projections of the impact of halogens on ozone depletion in the Antarctic stratosphere.   Carlos A. Cuevas, Rafael P. Fernandez, Douglas E. Kinnison, Qinyi Li, Jean-Francois Lamarque, Tarek Trabelsi, Joseph S. Francisco, Susan Solomon and Alfonso Saiz-Lopez. The influence of iodine on the Antarctic stratospheric ozone hole. Proceedings of the National Academy of Sciences. https://www.pnas.org/content/119/7/e2110864119