Example retrieved vertical profile of HCl during the Mars year 35 dust season. Panel a: ensemble of retrieved vertical profiles (shades of purple, as in Fig. 1) made for one occultation. Each line corresponds to a set of detector rows from which spectra were extracted. Panel b: corresponding ensemble of uncertainties. Panels a and b: the solid black lines show the weighted mean of the ensemble of retrievals, and the uncertainty (standard error). The dashed black lines are for a retrieval made using the mean spectra shown in Fig. 1.