The mixing ratio profile of N2O5 has been inferred from high-resolution emission spectra obtained with a balloon-borne Fourier spectrometer (SIRIS). The observations were taken for the period from midnight to predawn on September 16, 1986 at 32¿ N latitude. The inferred volume mixing ratio from nighttime average spectra has a peak of ~1.8¿10-9 in the 32--35 altitude range. The inferred mixing ratio is generally less than the theoretical predictions from a 1-D model. ¿ American Geophysical Union 1988