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

Abstract

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 NO2 column amounts of MIPAS and DOAS increased from 1 x 1015 cm-2 in December to ~3 x 1015 cm-2 in March. After sunset MIPAS observed strong NO2 increases, up to 3.2 x 1015 cm-2 on December 20, up to 7.2 x 1015 cm-2 on January 17 and up to 6.4 x 1015 cm-2 on March 27. These high nighttime values, showing considerable amounts of NOx in the midlatitude stratosphere, were qualitatively reproduced by SLIMCAT. The NO2 columns measured inside the Arctic vortex, ≤ 1 x 1015 cm-2 from December until mid-January with no substantial increase after sunset, displayed strong denoxification. From the end of Janaury the Arctic daytime NO2 columns grew to ~ 2 x 1015 cm-2, and after sunset MIPAS observed similar strong increases as at midlatitudes, up to 3.4 x 1015 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 1015 cm-2 after reaching the maximum, caused by N2O5 and ClONO2 formation and encounter of less renoxified air masses.