EC-16. Detection of IO radicals over the continental U.S.: Implications for gaseous mercury oxidation from the troposphere into the stratosphere

Abstract
The role of atmospheric iodine atom as an oxidant of gaseous elemental mercury (GEM) has been deemed unimportant due to the relatively low amounts of iodine in the troposphere and the much faster thermal decomposition rate of the Hg-I adduct compared to Hg-Br and Hg-OH adducts. As a result, the latest implementation of atmospheric mercury chemistry in GEOS-Chem does not include reactions involving iodine atoms or iodine monoxide radicals (IO). Here, we re-examine the contribution of iodine atom and IO to the oxidation of GEM using co-located ground-based and airborne measurements of IO, BrO, NO2, O3, CO, CH4, GEM, oxidized mercury, and meteorology at Storm Peak Laboratory (SPL), Colorado (40.455 N, 106.744 W) during the TI3GER (Technological Innovation Into Iodine and GV-Aircraft Environmental Research) campaign in April 2022. These measurements, along with GEOS-Chem model output, are used to constrain a vertical profile of box model simulations utilizing the Framework for 0-D Atmospheric Modeling (F0AM). Results from this case study are contextualized using long-term observations of IO at SPL.