Scatter plots of model HCl VMRs versus (top left) water vapour VMRs, (top right) temperature, (bottom left) water ice opacity, and (bottom right) dust opacity, sampled at each ACS MIR occultation where HCl was retrieved during MY 34 and MY 35. Only data from the altitudes where HCl was successfully retrieved are considered. Points with zero ice opacity are arbitrarily assigned an opacity of 1 × 10⁻⁴⁵ km⁻¹. The colour scale indicates point density, increasing from blue to red.