Model production (left) and loss (middle) rates of HCl corresponding to the ACS HCl detection from Fig. 5, where modelled HCl is lower than observed by ACS. The right panel shows model (solid line) and MCS (closed circles) water ice and dust opacity profiles. The MCS data are taken as close as possible in space and time to the ACS MIR HCl observation. Model profiles are averaged over the 5° L_S interval containing the observation; standard deviations are omitted here for clarity.