Atmos. Chem. Phys. Discuss., 11, 13769-13827, 2011
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Emission sources contributing to tropospheric ozone over equatorial Africa during the summer monsoon
I. Bouarar1, K. S. Law1, M. Pham1, C. Liousse2, H. Schlager3, T. Hamburger3, C. E. Reeves4, J.-P. Cammas2, P. Nédéléc2, S. Szopa5, F. Ravegnani6, S. Viciani7, F. D'Amato7, A. Ulanovsky8, and A. Richter9
1UPMC Univ. Paris 06; Univ. Versailles Saint-Quentin; CNRS/INSU, UMR 8190, LATMOS/IPSL, Paris, France
2Université de Toulouse; Laboratoire d'Aérologie, CNRS, UMR 5560, Toulouse, France
3Institut für Physik der Atmosphäre, DLR, Oberpfaffenhofen, Germay
4School of Environmental Sciences, University of East Anglia, Norwich, UK
5Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL, CEA-CNRS-UVSQ, UMR 8212, Gif-sur-Yvette, France
6Institute of Atmospheric Sciences and Climate (ISAC-CNR), Bologna, Italy
7Consiglio Nazionale dell Ricerche-Istituto Nazionale di Ottica (CNR-INO), Firenze, Italy
8Central Aerological Observatory, Moscow, Russia
9Institute of Environmental Physics, University of Bremen, Bremen, Germany

Abstract. A global chemistry-climate model LMDz_INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over central and West Africa during the summer monsoon. The model results show that ozone in this region is most sensitive to lightning NOx and to central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NOx occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere into higher altitudes by the deep convection that occurs over West Africa during the monsoon season, dominate the ozone changes in the upper troposphere and lower stratosphere region. Convective uplift of soil NOx emissions over the Sahel region also makes a significant contribution to ozone in the upper troposphere. Concerning African anthropogenic emissions, they make a lower contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The influence of Asian emissions should also be taken into account in studies of the ozone budget over Africa since they make a considerable contribution to ozone concentrations above 150 hPa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report) estimates of anthropogenic emissions for 2030 over Africa and Asia, the model calculations suggest largest changes in ozone due to the growth of emissions over Asia than over Africa over the next 20 years.

Citation: Bouarar, I., Law, K. S., Pham, M., Liousse, C., Schlager, H., Hamburger, T., Reeves, C. E., Cammas, J.-P., Nédéléc, P., Szopa, S., Ravegnani, F., Viciani, S., D'Amato, F., Ulanovsky, A., and Richter, A.: Emission sources contributing to tropospheric ozone over equatorial Africa during the summer monsoon, Atmos. Chem. Phys. Discuss., 11, 13769-13827, doi:10.5194/acpd-11-13769-2011, 2011.
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