Airborne remote sensing of NO2 in the Arctic winter of 1994-1995 and comparison with a three-dimensional chemical transport model

In the winter of 1994-1995, for the first time NO2 was observed by the Michelson Interferometer for Passive Atmospheric Sounding-Flugzeug Transall (MIPAS-FT). We present the NO2 data of MIPAS and of a Differential Optical Absorption Spectroscopy (DOAS) instrument, which was also operated on the Transall, and compare the measurements with the Single Layer Isentropic Model for Chemistry And Transport (SLIMCAT). The daytime midlatitude NO:! column amounts of MIPAS and DOAS increased from 1 x 10(15) cm(-2) in December to similar to 3 x 1015 cm-2 in March. After sunset MIPAS observed strong NO2 increases, up to 3.2 x 10(15) cm(-2) on December 20, up to 7.2 x 10(15) cm(-2) on January 17 and up to 6.4 x 10(15) cm(-2) on March 21. These high nighttime values, showing considerable amounts of NO2 in the midlatitude stratosphere, were qualitatively reproduced by SLIMCAT. The NO2 columns measured inside the Arctic vortex, less than or equal to 1 x 10(15) cm(-2) from December until mid-January with no substantial increase after sunset, displayed strong denoxification. From the end of January the Arctic daytime NO2 columns grew to similar to 2 x 10(15) cm(-2), and after sunset MTPAS observed similar strong increases as at midlatitudes, up to 3.4 x 10(15) cm(-2) on January 24 and up to 4.8 x 1015 cm-2 in March and April. The renoxification of the vortex was also shown by SLIMCAT. On April 5, MIPAS NO2 column amounts decreased by 1.5 x 10(15) cm(-2) after reaching the maximum, caused by N2O5 and ClONO2 formation and encounter of less renoxified air masses.