MIPAS measurements of upper tropospheric C2H6 and O3 during the southern hemispheric biomass burning season in 2003

Under cloud free conditions, the Michelson Inter- ferometer for Passive Atmospheric Sounding (MIPAS) pro- vides measurements of spectrally resolved limb radiances down to the upper troposphere. These are used to infer global distributions of mixing ratios of atmospheric constituents in the upper troposphere and the stratosphere. From 21 October to 12 November 2003, MIPAS observed enhanced amounts of upper tropospheric C2H6 (up to about 400 pptv) and ozone (up to about 80 ppbv). The absolute values of C2H6, how- ever, may be systematically low by about 30% due to uncer- tainties of the spectroscopic data used. By means of trajec- tory calculations, the enhancements observed in the southern hemisphere are, at least partly, attributed to a biomass burn- ing plume, which covers wide parts of the Southern hemi- sphere, from South America, the Atlantic Ocean, Africa, the Indian Ocean to Australia. The chemical composition of the part of the plume-like pollution belt associated with South American fires, where rainforest burning is predominant ap- pears different from the part of the plume associated with southern African savanna burning. In particular, African sa- vanna fires lead to a larger ozone enhancement than equa- torial American fires. In this analysis, MIPAS observations of high ozone were disregarded where low CFC-11 (below 245 pptv) was observed, because this hints at a stratospheric component in the measured signal. Different type of vege- tation burning (flaming versus smouldering combustion) has been identified as a candidate explanation for the different plume compositions.