Effects of regional-scale and convective transports on tropospheric ozone chemistry revealed by aircraft observations during the wet season of the AMMA campaign G. Ancellet1, J. Leclair de Bellevue1, C. Mari2, P. Nedelec2, A. Kukui1, A. Borbon3, and P. Perros3 1Service d'Aéronomie, Université Paris 6, Université Versailles-St-Quentin, CNRS, France 2Université de Toulouse, CNRS, LA (Laboratoire d'Aérologie), France 3Laboratoire Interuniversitaire des Systèmes Atmosphériques, Université Paris 12, CNRS, France
Abstract. The African Monsoon Multidisciplinary Analyses (AMMA) fourth airborne
campaign was conducted in July–August 2006 to study the chemical
of the middle and upper troposphere in West Africa with the major objective
to better understand the processing of chemical emissions by the West
Monsoon (WAM) and its associated regional-scale and vertical transports.
In particular, the french airborne experiment was organized around two
The first was to characterize the impact of Mesoscale Convective Systems
on the ozone budget in the upper troposphere and the evolution of the
chemical composition of these convective plumes as they move westward
the Atlantic Ocean. The second objective was to discriminate the impact of
remote sources of pollution over West Africa, including transport from the
middle east, Europe, Asia and from southern hemispheric fires.
Observations of O3, CO, NOx, H2O and hydroperoxide above West Africa along
repeated meridional transects were coupled with transport analysis
based on the FLEXPART lagrangian model. The cross analysis of trace gas
transport pathways revealed 5 types of air masses:
convective uplift of industrial and urban emissions,
convective uplift of biogenic emissions,
slow advection from Cotonou polluted plumes near the coast,
meridional transport of upper
tropospheric air from the subtropical barrier region,
and meridional transport of Southern Hemisphere (SH) biomass burning
correlation plots and the correlation plots of H2O2 with a OH proxy
revealed not only a control of the trace gas variability by transport
processes but also significant photochemical reactivity in the mid- and upper
The study of four MCSs outflow showed contrasted chemical composition
and air mass origins depending on the MCSs lifetime and latitudinal position.
Favorables conditions for ozone production were found for MCSs with
increased MCS lifetime (>1.5 days), which allowed for more H2O2 formation,
with trajectories crossing the 10° N latitude, which increased
CO transport to the upper troposphere.
The upper tropospheric concentrations sampled in the MCS outflow regions
showed mixed origins including local vertical convective transport,
and uplifting of air from the low troposphere over the middle-east
related to the summer Asian low pressure system or from the southern
Citation: Ancellet, G., Leclair de Bellevue, J., Mari, C., Nedelec, P., Kukui, A., Borbon, A., and Perros, P.: Effects of regional-scale and convective transports on tropospheric ozone chemistry revealed by aircraft observations during the wet season of the AMMA campaign, Atmos. Chem. Phys., 9, 383-411, doi:10.5194/acp-9-383-2009, 2009.