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Upper tropospheric pollution observed by MIPAS HCN and C2H6 global distributions

Norbert Glatthor(1), Thomas von Clarmann(1), Gabriele P. Stiller(1), Bernd Funke(2), Mariliza Koukouli(3), Herbert Fischer(1), Udo Grabowski(1), Michael Höpfner(1), Sylvia Kellmann(1) and Andrea Linden(1)

(1) Forschungszentrum/Universität Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany
(2) Instituto de Astrofisica de Andalucia, Postal 2144, 18008 Granada, Spain
(3) Aristotle University of Thessaloniki, , 54124 Thessaloniki, Greece

Abstract

We present global upper tropospheric HCN and C2H6 amounts derived from MIPAS/ENVISAT limb emission spectra. The datasets consists of 54 days between September 2003 and March 2004. This period covers the peak and decline of the southern hemispheric biomass burning period and some months thereafter. HCN is a nearly unambiguous tracer of biomass burning with an assumed tropospheric lifetime of several months. Indeed, the most significant feature in the MIPAS HCN dataset is an upper tropospheric plume of enhanced values caused by southern hemispheric biomass burning, which in September and October 2003 extended from tropical South America over Africa, Australia to the Southern Pacific. The spatial extent of this plume agrees well with the MOPITT CO distribution of september 2003. The MIPAS HCN plume extended from the lowermost observation height (8 km) up 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. The main sources of C2H6 are production and transmission of fossil fuels, followed by biofuel use and biomass burning. The C2H6 distribution also clearly reflected the southern hemispheric biomass burning plume and its seasonal variation, with maximum amounts of 600--700 pptv. Generally there was good agreement between the southern hemispheric distributions of both pollution tracers, except for the region between Peru and the mid-Pacific. Here C2H6 was considerably enhanced, whereas the HCN amounts were low. Backward trajectory calculations suggested that industrial pollution was responsible for the elevated C2H6 in these particular air masses.

Except for the Asian monsoon anticyclone in September 2003, there were only comparably small regions of enhanced HCN in the northern hemisphere. However, C2H6 showed an equally strong northern hemispheric signal between the equator and low midlatitudes, persisting over the whole observation period. Backward trajectory calculations for air masses from this region also pointed to industrial sources of this pollution.