Observations of two C₂H₂ lines from VLT/VISIR on July 26 (dots) and August 13 (diamonds). As absolute calibration proved difficult for these spectra, the plots are expressed as a line-to-continuum ratio, with the continuum defined by a mean of the uncalibrated flux either side of the emission features. The “dip” of the continuum is an artefact of poorly-corrected telluric absorption. Models of the expected ratio, based on scaling the C₂H₂ profiles of Nixon et al. (2007), are shown as dotted lines for comparison. The same models were used for panels a) and b), indicating the difficulty in determining a unique profile of C₂H₂ from this dataset.