VERTICAL PROFILES OF N2O5 ALONG WITH CH4, N2O, AND H2O IN THE LATE ARCTIC WINTER RETRIEVED FROM MIPAS-B INFRARED LIMB EMISSION MEASUREMENTS

Vertical profiles of N2O5, CH4, N2O, and H2O inside the arctic vortex were retrieved from nighttime infrared limb emission spectra obtained during a flight of the Michelson interferometer for passive atmospheri c sounding, balloonborne version (MIPAS-B) Fourier spectrometer from K iruna (Sweden, 68 degrees N) on March 14/15, 1992, as part of the Euro pean Arctic Stratospheric Ozone Experiment. Spectra were analyzed by a nonlinear multiparameter least squares fitting procedure in combinati on with an onion-peeling retrieval algorithm. The N2O5 results were de rived from the intensity of the via band near 8 mu m. These data repre sent the first ever reported N2O5 profile inside the polar vortex. Bet ween 21.5 and 31.7 km altitude, N2O5 mixing ratios from 0.38 to 0.74 p arts per billion by volume (ppbv) were inferred. Below 21.5 km there i s a steep decrease in the mixing ratio toward values lower than 0.07 p pbv at 18.9 and 16.1 km. This discontinuity in the vertical profile co rrelates in altitude with the bulk of the Pinatubo aerosol layer insid e the arctic vortex. N2O5 concentrations are calculated as a function of time since local sunset by using initial NO2 concentrations, O-3 co ncentrations, aerosol surface area densities, and reaction rate coeffi cients, as found in the literature; calculated N2O5 concentrations are consistent with the MIPAS results. These suggest efficient heterogene ous hydrolysis of N2O5 having taken place on sulphate aerosol particle s. Retrieved CH4 and N2O profiles reflect the subsided polar vortex ai r.