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 N2O5 analysis spectral region to its value in a N2O5-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 N2O5 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 NOy 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. N2O5 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.