Vertical profiles of C₃H₄ (top panels) and C₄H₂ (bottom panels) retrieved at 70°S in December 2014 (left panels) and 45°N in September 2012 (right panels). Vertical profiles from retrievals (a) and their a priori are respectively represented by red solid and dashed lines. Vertical profiles from retrievals (b) are represented by blue solid lines. A priori profiles for retrievals (b) are represented by blue dashed lines within the pressure range probed by the CIRS limb observations, and by blue dotted lines outside this pressure range. Thin black dashed lines show the pressure range probed by our CIRS nadir observations. The limb profiles on the left and right panels (blue dashed lines) were respectively measured at 79°S in September 2014 and 46°N in June 2012. At the pressure levels probed by our observations, retrievals (a) and (b) give consistent results, except for C₄H₂ at 70°S in December 2014, because of the high vertical gradient of the a priori profile (b).