Comparison of column abundances from three infrared spectrometers during AASE II

Three Fourier transform infrared (FTIR) spectrometers were on board the NASA DC‐8 during the second Airborne Arctic Stratospheric Expedition (AASE II) in 1992. Two FTIRs used solar absorption and one used thermal emission. We compare over 2000 measurements from these 3 FTIRs, on 12 DC‐8 flights, for closely coincident air masses and times, both inside and outside the polar vortex. In the majority of cases the offset biases are quite small, in the range 1–4%, and comparable to the absolute precisions expected. In most cases the rms scatter is in the range 4–11%; this scatter is unlikely to be geophysical, but rather is probably instrumental or analytical in origin.