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Atmos. Chem. Phys. Discuss., 9, 17385-17427, 2009
www.atmos-chem-phys-discuss.net/9/17385/2009/ doi:10.5194/acpd-9-17385-2009 © Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. |
Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production
1LATMOS-Service d'Aéronomie/UPMC/UVSQ/IPSL, CNRS-INSU, 4 Place Jussieu, 75252, Paris, France
2ISAC-CNR Bologna, Italy
3Instituto di Scienze dell'Atmosfera e del Clima, Roma, Italy
4aMax Planck Institute for Chemistry, Particle Chemistry Dept., Germany
4bInstitute for Atmospheric Physics, Johannes Gutenberg University, Mainz, Germany
5Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Institut für Physik der Atmosphäre, 82230 Wessling, Germany
6Institut für Meteorologie und Geophysik, Universität Frankfurt, Frankfurt, Germany
7Institute for Climate and Atmospheric Science School of Earth and Environment, University of Leeds, UK
8Dept. of Chemistry, University of Reading, Reading, UK
9National Centre for Atmospheric Science Dept. of Chemistry, University of York, York, UK
10National Centre for Atmospheric Science, University of York, York, UK
11Institute of Atmospheric Sciences and Climate, CNR, Bologna, Italy
12CAO, Dolgoprudny, Russia
13Laboratoire d'Aérologie, Université de Toulouse, France
*now at: CEREA, ENPC/EDF, 20 rue Alfred Nobel 77455 - Champs sur Marne, France
Abstract. Pollutant plumes with enhanced levels of trace gases and aerosols were observed over the southern coast of West Africa during August 2006 as part of the AMMA wet season field campaign. Plumes were observed both in the mid and upper troposphere. In this study we examined both the origin of these pollutant plumes and their potential to produce O3 downwind over the Atlantic Ocean. Runs using the BOLAM mesoscale model including biomass burning CO tracers were used to confirm an origin from central African fires. The plumes in the mid troposphere had significantly higher pollutant concentrations due to the fact that transport occurred from a region nearer or even over the fire region. In contrast, plumes transported into the upper troposphere over West Africa had been transported to the north-east of the fire region before being uplifted. Modelled tracer results showed that pollutants resided for between 9 and 12 days over Central Africa before being transported for 4 days, in the case of the mid-troposphere plume and 2 days in the case of the upper tropospheric plume to the measurement location over the southern part of West Africa. Around 35% of the biomass burning tracer was transported into the upper troposphere compared to that remaining in the mid troposphere. Runs using a photochemical trajectory model, CiTTyCAT, were used to estimate the net photochemical O3 production potential of these plumes. The mid tropospheric plume was still very photochemically active (up to 7 ppbv/day) especially during the first few days of transport westward over the Atlantic Ocean. The upper tropospheric plume was also still photochemically active, although at a slower rate (1–2 ppbv/day). Trajectories show this plume being recirculated around an upper tropospheric anticyclone back towards the African continent (around 20° S). The potential of theses plumes to produce O3 supports the hypothesis that biomass burning pollutants are contributing to the observed O3 maxima over the southern Atlantic at this time of year.
Citation: Real, E., Orlandi, E., Law, K. S., Fierli, F., Josset, D., Cairo, F., Schlager, H., Borrmann, S., Kunkel, D., Volk, M., McQuaid, J. B., Stewart, D. J., Lee, J., Lewis, A., Hopkins, J. R., Ravegnani, F., Ulanovski, A., and Liousse, C.: Cross-hemispheric transport of central African biomass burning pollutants: implications for downwind ozone production, Atmos. Chem. Phys. Discuss., 9, 17385-17427, doi:10.5194/acpd-9-17385-2009, 2009.