Diurnal and nocturnal distribution of stratospheric NO2 from solar and stellar occultation measurements in the Arctic vortex: Comparison with models and ILAS satellite measurements

NO2 mixing ratio profiles were measured at sunset between 14 and 30 km usin g the Limb Profile Monitor of the Atmosphere (LPMA) experiment and during t he night between 13 and 31 km using the Absorption par Minoritaires Ozone e t NOx (AMON) experiment inside the Arctic vortex, both on February 26, 1997 . Coinciding profiles measured by the Improved Limb Atmospheric Spectromete r (ILAS) instrument on board ADEOS have been used to check the consistency between the satellite and balloon profiles for NO2, O-3, and HNO3. A box mo del has been used for the photochemical correction of the LPMA NO2 profiles at sunset. The resulting NO2 balloon-borne profiles of LPMA and AMON are c ompared to each other after accounting for the day/night photochemical vari ation using the box model initialized with measurements. The comparisons th us performed show an average difference less than 9% between the two measur ements (considered to sample similar air masses) when the box model is init ialized with little chlorine activation (i.e., when the major burden of chl orine is stored in ClONO2) for a 1 day integration. The comparison with the Reprobus 3-D chemistry transport model (CTM) seasonal simulations clearly confirms an underestimation of NO2 by the model below 25 km, in the altitud e range where aerosols lead to a complete removal of NOx in the model. Rece nt updates of rate coefficients for conversion of HNO3 into NO2 only slight ly improve the NO2 model results in vortex conditions. These results sugges t that a source of NO2 is still lacking in the CTM.