Large-scale upper tropospheric pollution observed by MIPAS HCN and C2H6 global distributions 1KIT – Karlsruher Institut für Technologie, Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany
2Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain
3Laboratory of Atmospheric Physics, Physics Department, Aristotle University of Thessaloniki, Thessaloniki, Greece
Received: 06 Apr 2009 – Published in Atmos. Chem. Phys. Discuss.: 29 Jul 2009 Abstract. We present global upper tropospheric HCN and C2H6 amounts derived from MIPAS/ENVISAT
limb emission spectra. HCN and C2H6 are retrieved in the spectral regions
715.5–782.7 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 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. Further there is good agreement with the shapes and mixing ratios
of the southern hemispheric HCN and C2H6 fields measured by the ACE experiment between September
and November 2005. The MIPAS HCN plume extended from the lowermost observation height of 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,
confirming the assumed tropospheric lifetime. 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
spatial overlap between the southern hemispheric distributions of both pollution tracers, except for the
region between Peru and the mid-Pacific. Here C2H6was considerably enhanced, whereas the
HCN amounts were low. Backward trajectory calculations suggested that industrial pollution was responsible
for the elevated C2H6 concentration in these particular air masses.
Revised: 03 Dec 2009 – Accepted: 08 Dec 2009 – Published: 22 Dec 2009
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 point to industrial sources of this pollution. Generally, C2H6/HCN
ratios 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 biomass
Citation: Glatthor, N., von Clarmann, T., Stiller, G. P., Funke, B., Koukouli, M. E., Fischer, H., Grabowski, U., Höpfner, M., Kellmann, S., and Linden, A.: Large-scale upper tropospheric pollution observed by MIPAS HCN and C2H6 global distributions, Atmos. Chem. Phys., 9, 9619-9634, doi:10.5194/acp-9-9619-2009, 2009.