AIRBORNE REMOTE-SENSING OF NO2 IN THE ARCTIC WINTER OF 1994-1995 AND COMPARISON WITH A 3-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 Tr ansall (MIPAS-FT). We present the NO2 data of MIPAS and of a Different ial 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 day time 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. Af ter 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 qual itatively reproduced by SLIMCAT. The NO2 columns measured inside the A rctic vortex, less than or equal to 1 x 10(15) cm(-2) from December un til mid-January with no substantial increase after sunset, displayed s trong denoxification. From the end of January the Arctic daytime NO2 c olumns grew to similar to 2 x 10(15) cm(-2), and after sunset MTPAS ob served 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. Th e 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 reachi ng the maximum, caused by N2O5 and ClONO2 formation and encounter of l ess renoxified air masses.