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

NO 2 mixing ratio profiles were measured at sunset between 14 and 30 km using the Limb Profile Monitor of the Atmosphere (LPMA) experiment and during the night between 13 and 31 km using the Absorption par Minoritaires Ozone et NO x (AMON) experiment inside the Arctic vortex, both on February 26, 1997. Coinciding profiles measured by the Improved Limb Atmospheric Spectrometer (ILAS) instrument on board ADEOS have been used to check the consistency between the satellite and balloon profiles for NO 2 , O 3 , and HNO 3 . A box model has been used for the photochemical correction of the LPMA NO 2 profiles at sunset. The resulting NO 2 balloon‐borne profiles of LPMA and AMON are compared to each other after accounting for the day/night photochemical variation using the box model initialized with measurements. The comparisons thus performed show an average difference less than 9% between the two measurements (considered to sample similar air masses) when the box model is initialized with little chlorine activation (i.e., when the major burden of chlorine is stored in ClONO 2 ) for a 1 day integration. The comparison with the Reprobus 3‐D chemistry transport model (CTM) seasonal simulations clearly confirms an underestimation of NO 2 by the model below 25 km, in the altitude range where aerosols lead to a complete removal of NO x in the model. Recent updates of rate coefficients for conversion of HNO 3 into NO 2 only slightly improve the NO 2 model results in vortex conditions. These results suggest that a source of NO 2 is still lacking in the CTM.