Stratospheric N₂O₅ in the austral spring 2002 as retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

N₂O₅ was retrieved from infrared limb emission spectral radiances made by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European environmental satellite (ENVISAT). The measurements were taken during the period covering the Antarctic polar vortex split between 20 September and 13 October 2002. The retrieval of N₂O₅ is aggravated by its continuum-like emission feature covering a wide spectral region, which is hardly distinguishable from background continuum emission. The method of constraining the background continuum in the N₂O ₅ analysis spectral region to its value in a N ₂O₅-free spectral region was found to be appropriate to solve this problem. Retrieved volume mixing ratios (VMR) of N₂O₅ exhibit features consistent with the dynamics prevalent at the time in the Antarctic and known N ₂O₅ chemistry governing diurnal variability. The observations of low N₂O₅ inside vortex air mass and rich N₂O₅ exvortex air mass are strongly in support of the chemistry that governs its partitioning within the NO _y family. The enhanced nighttime high geographic latitude N₂O₅ VMR with a peak of 4.4 ppbv in the altitude range of 32-37 km during the last week of September 2002 is consistent with air mass transport from lower to high latitudes and temperature-sensitive N₂O₅ formation chemistry. N ₂O₅ enhancement up to 6 ppbv was also observed by the Cryogenic Limb Array Etalon Spectrometer(CLAES) and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on Upper Atmospheric Research Satellite (UARS) during Northern Hemisphere January 1992 stratospheric warming which was a factor of 3 larger than any measurements of N₂O₅ prior to UARS. In contrast, a maximum of 4.4 ppbv N₂O₅ VMR observed by MIPAS at 32-37 km is only a factor of 2 larger than its prewarming values.