m/z 16 to m/z 28 count ratios in GCMS data versus altitude recorded during Huygens descent. Black dots correspond to raw counts archived in level 2 data requiring no correction. Blue dots correspond to raw counts for which a correction is required and red dots correspond to corrected counts using m/z 29 as a proxy when m/z 28 saturates. We note that the very sharp increase in counts at altitude 0 corresponds to outgassing after Huygens’s touchdown and GCMS continued recording atmospheric mass spectra for a couple of hours after the touchdown (not shown here). A comparison between the two correction methods using either m/z 14 or 29 as a proxy is given in Figure A.1.