We have used a Fourier transform spectrometer aboard the NASA DC‐8 aircraft during the Airborne Arctic Stratospheric Expedition (AASE) to record infrared absorption spectra of the polar stratosphere. From these high resolution spectra we have derived vertical column amounts above flight altitude of O₃, CH₄, N₂O, H₂O, HCl, HF, NO, NO₂, ClONO₂, and HNO₃ for eleven flights poleward of 60°N. We report here measurements on the flight of 26 January 1989 when the flight path during the observations crossed from outside the polar vortex to inside. This allowed a clear comparison of the conditions of the air within the vortex with that outside. Observations of passive tracers such as CH₄ and HF indicate that air of a certain composition within the polar vortex occurs at lower altitude than air outside. Within the vortex, we observed markedly reduced columns of HCl and NO₂. The ratio of HCl to HF column dropped from its typical nidlatitude value of 4.5 to as low as 1.7 within the vortex, implying that the HCl had been chemically or physically removed from the air in the vortex. NO₂ values within the vortex were near 3.0×10¹⁴ molecules‐cm⁻², about a factor of two less than columns outside. In contrast to the Antarctic observations, HNO₃ values were elevated within the vortex. HNO₃ columns inside the vortex reached values of 30×10¹⁵ molecules‐cm⁻². The ClONO₂ column was largest within the vortex, peaking at 4×l0¹⁵ molecules‐cm⁻² near the boundary of the vortex, and decreasing farther into the vortex.