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We present global upper tropospheric HCN and C2H6 amounts derived from MIPAS/ENVISATlimb emission spectra. HCN and C2H6 are retrieved in the spectral regions715.5–782.7 cm−1 and 811.5–835.7 cm−1, respectively.The datasets consist of 54 days between September 2003 and March 2004.This period covers the peak and decline of the southern hemispheric biomass burning period and somemonths thereafter. HCN is a nearly unambiguous tracer of biomass burning with an assumed troposphericlifetime of several months.Indeed, the most significant feature in the MIPAS HCN dataset is an upper tropospheric plumeof enhanced values caused by southern hemispheric biomass burning, which in Septemberand October 2003 extended from tropical South America over Africa, Australia to theSouthern Pacific. The spatial extent of this plume agrees well with the MOPITT COdistribution of September 2003. Further there is good agreement with the shapes and mixing ratiosof the southern hemispheric HCN and C2H6 fields measured by the ACE experiment between Septemberand November 2005. The MIPAS HCN plume extended from the lowermost observation height of 8 kmup to about 16 km altitude, with maximum values of 500–600 pptv in October 2003.It was still clearly visible in December 2003, but had strongly decreased by March 2004,confirming the assumed tropospheric lifetime. The main sources of C2H6 are production andtransmission of fossil fuels, followed by biofuel use and biomass burning.The C2H6 distribution also clearly reflected the southern hemispheric biomass burning plumeand its seasonal variation, with maximum amounts of 600–700 pptv. Generally there was goodspatial overlap between the southern hemispheric distributions of both pollution tracers, except for theregion between Peru and the mid-Pacific. Here C2H6was considerably enhanced, whereas theHCN amounts were low. Backward trajectory calculations suggested that industrial pollution was responsiblefor the elevated C2H6 concentration in these particular air masses. Except for the Asian monsoon anticyclone in September 2003, there were only comparably smallregions of enhanced HCN in the Northern Hemisphere. However, C2H6 showed an equally strongnorthern hemispheric signal between the equator and low midlatitudes, persisting over thewhole observation period. Backward trajectory calculations for air masses from this regionalso point to industrial sources of this pollution. Generally, C2H6/HCNratios between 1 and 1.5 indicate biomass burning and ratios larger than 1.5 industrial pollution.However, in March 2004 ratios of up to 2 were also found in some regions of the former southern biomassburning plume

atmospheric chemistry and physics

Large-scale upper tropospheric pollution observed by MIPAS HCN and C&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;H&amp;lt;sub&amp;gt;6&amp;lt;/sub&amp;gt; global distributions