Spatial and temporal variability of ClONO2, HNO3, and O3 in the Arctic winter of 1992/1993 as obtained by airborne infrared emission spectroscopy

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Abstract
In the winter of 1992/1993 the airborne Michelson interferometer for passive atmospheric sounding (MIPAS‐FT) was operated on board a German research aircraft (Transall C‐160) to record infrared emission spectra of the atmosphere inside and outside the Arctic vortex. Measurements were made during four campaigns between December 4, 1992, and March 29, 1993, in the European Arctic as well as over central and southern Europe (82°N–37.5°N). We present the retrieved zenith column amounts of the stratospheric trace gases ClONO2, HNO3, and O3 of this period. Inside the polar vortex, the column amounts of ClONO2 and HNO3 were considerably enhanced already in early December, up to 3.1×1015 cm−2 and 2.7×1016 cm−2, respectively. Around the end of January, low ClONO2 (1×1015 cm−2) and high HNO3 column amounts (up to 3.7×1016 cm−2) were observed inside the vortex, whereas a highly variable “collar” of ClONO2 had developed at the vortex edge. During March, after temperatures had been above the threshold for polar stratospheric clouds (PSCs) for several weeks, we measured lower HNO3 (below 2.5×1016 cm−2) and very high ClONO2 column amounts (up to 6×1015 cm−2) inside the vortex. Thus a major part of the reactive chlorine had been converted into ClONO2, and the potential for rapid ozone depletion was reduced markedly in the region observed. On March 10, when the polar vortex extended southward to the Mediterranean, ClONO2 column amounts as high as 4.6×1015 cm−2 were observed at 40°N. At the end of March, considerable amounts of ClONO2 (up to 3.4×1015 cm−2) were measured also far outside the vortex.

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