Tropical Cyclones Drive Enhanced Inorganic Iodine in the Mid‐Latitude Upper Troposphere

Abstract Halogens deplete tropospheric and stratospheric ozone, but the role of iodine is still elusive. Atmospheric iodine mainly originates from marine inorganic (I 2 , HOI) and organic (CH 3 I, CH 2 I 2 , CH 2 IBr, and CH 2 ICl) emissions. We report on airborne measurements of atmospheric iodine oxide (IO) concentrations up to 15 km altitude from two flights of the WISE campaign over the mid‐Atlantic in September and October 2017. IO is retrieved from limb scattered skylight in the upper troposphere (UT) using the airborne mini‐DOAS instrument on board the German High Altitude and LOng range research aircraft (HALO). Elevated IO (maximum , mean over ) was observed in the UT in air masses processed by category 5 hurricanes Irma and Maria. Our findings show that enhanced IO mixing ratios are driven by fast vertical transport through tropical cyclones and potentially enhanced marine iodine emissions due to associated high surface winds.