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Title: Life's Biological Chemistry: A Destiny or Destination Starting from Prebiotic Chemistry?
Author(s) / Creator(s):
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Chemistry - A European Journal
Page Range / eLocation ID:
p. 16708-16715
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract. 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 3 %–4 % reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30 ppbv less ozone at low latitudes and up to 100 ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5 %–10 % depending on geographical location. In the lower troposphere, 75 % of the modeled ozone reduction originates from inorganic sources of iodine, 25 % from organic sources of iodine. At 50 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 1.5 %–2.5 %. 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. 
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    As the chemical and physical state of the stratosphere evolves, so too will the rates of important ozone-destroying reactions. In this work, we evaluate the chemistry-climate sensitivity of reactions of stratospheric iodine, reporting the iodine alpha factor (the efficiency of ozone loss mediated by a single iodine atom relative to the ozone loss mediated by a single chlorine atom) and the iodine eta factor (the efficiency of ozone loss mediated by a single iodine atom relative to the ozone loss mediated by a single chlorine atom in a benchmark chemistry-climate state) as a function of future greenhouse gas emissions scenario. We find that iodine-mediated ozone loss is much less sensitive to future changes in the state of the stratosphere than chlorine- and bromine-mediated reactions. Additionally, we demonstrate that the inclusion of the heterogeneous reaction of ozone with aqueous iodide in stratospheric aerosol produces substantial enhancements in the iodine alpha and eta factors relative to evaluations that consider gas-phase iodine reactions only. We conclude that the share of halogen-induced ozone loss due to reactions of iodine will likely be greater in the future stratosphere than it is today. 
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