Iodine chemistry in the chemistry-climate model SOCOL-AERv2-I

In this paper, we present a new version of the chemistry-climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3ĝ€¯%-4ĝ€¯% reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30ĝ€¯ppbv less ozone at low latitudes and up to 100ĝ€¯ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5ĝ€¯%-10ĝ€¯% depending on geographical location. In the lower troposphere, 75ĝ€¯% of the modeled ozone reduction originates from inorganic sources of iodine, 25ĝ€¯% from organic sources of iodine. At 50ĝ€¯hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5ĝ€¯%-2.5ĝ€¯%. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species.