Abstract
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 to higher altitudes by the deep convection that occurs over West Africa during the monsoon season, lead to maximum ozone changes in the lower stratosphere region. Soil NOx emissions over the Sahel region make a significant contribution to ozone in the lower troposphere. In addition, convective uplift of these emissions and subsequent ozone production are also an important source of ozone in the upper troposphere over West Africa. Concerning African anthropogenic emissions, they only make a small 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 import of Asian emissions also makes a considerable contribution to ozone concentrations above 150 hPa and has to be taken into account in studies of the ozone budget over Africa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report) estimates of anthropogenic emissions for 2030 over Africa and Asia, model calculations show larger changes in ozone over Africa due to growth in Asian emissions compared to African emissions over the next 20 yr.
Highlights
Tropospheric ozone (O3) plays an important role in the global climate and chemical composition of the atmosphere
Data from the satellite instruments MOPITT (Measurement Of Pollution In The Troposphere) and SCIAMACHY (Scanning Imaging Absorption spectrometer for Atmospheric CHartographY), and aircraft measurements from the African Monsoon Multidisciplinary Analyses (AMMA) and MOZAIC programs are presented in the first section
Control run based on the Emanuel (1993) convection scheme Lightning emissions reduced by 20 % Biomass burning emissions reduced by 20 % Biogenic volatile organic compounds (VOCs) reduced by 20 % Soil NOx emissions reduced by 20 % Anthropogenic emissions reduced by 20 % Asian emissions (70◦ E–120◦ E, 10◦ S–40◦ N) reduced by 20 % Lightning emissions increased by 50 % Convective transport and lightning NOx switched off over Africa Simulation using the Tiedtke (1989) convection scheme Simulation using anthropogenic emissions over Africa and Asia from the IPCC RCP45 scenario for 2030
Summary
Tropospheric ozone (O3) plays an important role in the global climate and chemical composition of the atmosphere. We examine the influence of different emissions on the distribution of tropospheric O3 over West and Central Africa as well as downwind over the Central Atlantic Ocean during the summer monsoon in 2006. For this purpose, we use the three-dimensional global chemistry model LMDz INCA. BB provided the largest impact on surface O3 concentrations during the monsoon season in their study They concluded that, in all seasons, African and global tropospheric O3 burdens are more sensitive to biogenic emissions than to BB, lightning NOx (LiNOx hereafter) and anthropogenic emissions.
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