TI3GER

The upper troposphere and lower stratosphere (UTLS) is a source of new particles, ambient ions, and a sink of ozone that is relevant for ozone radiative forcing, stratospheric dynamics, and climate sensitivities. A recent analysis of 30 years of ozone profile measurements revealed the lack of an anticipated recovery of lower stratospheric ozone under the Montreal Protocol. Ball et al. (2018) concluded that "the reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established." Global models that assess the recovery of the ozone layer do not represent iodine chemistry, which has been recognized (for the first time in more than a decade) by the 2018 WMO Ozone Assessment report, citing first measurements of iodine oxide (IO) radicals in the UT aboard the NSF/NCAR GV (i.e., TORERO project; Volkamer et al., 2015). Only very recently, the first quantitative detection of IO in the stratosphere was accomplished (i.e., CONTRAST project; Koenig et al., 2020). However, the amount of iodine injected into the stratosphere was uncertain due to a lack of simultaneous aircraft measurements that quantify gas and particulate iodine in the UTLS, which is now possible with existing technology that requires certification to fly on the GV.