The GMI combined tropospheric-stratospheric chemical mechanism was first described in Duncan et al. [2007]. The stratospheric portion of the mechanism came from the Lawrence Livermore National Lab ‘Impact’ model [Rotman et al., 2004, and references therein], while the tropospheric component was originally developed for the Harvard University GEOS-Chem tropospheric CTM [Horowitz et al., 1998].