Interactions of atmospheric gases and aerosols with the monsoon dynamics over the Sudano-Guinean region during AMMA

Carbon monoxide, CO, and fine atmospheric particulate matter, PM 2.5 , are analyzed over the Guinean gulf coastal region using the WRF-CHIMERE modeling system and observations during the beginning of the monsoon 2006 (from May to July), corresponding to the Africa Multidisciplinary Monsoon Analysis (AMMA) campaign period. Along the Guinean gulf coast, the contribution of long-range pollution transport to CO or PM 2.5 concentrations is important. For PM 2.5 , desert dust decreases from ≈38 % in May to ≈5 % in July; biomass burning aerosol from Central Africa increases from ≈10 % in May to ≈52 % in July. The anthropogenic contribution is ≈30 % for CO and ≈10 % for PM 2.5 . When focusing only on anthropogenic pollution, frequent northward transport events from the coast to the Sahel are associated with periods of low wind and no precipitation. In June, anthropogenic PM 2.5 and CO concentrations are higher than in May or July over the Guinean coastal region. Over the Sahel, air masses dynamics concentrate pollutants emitted locally and remotely at the coast due to a meridional atmospheric cell. Refining the analysis on the period 8–15 June, anthropogenic pollutants emitted along the coastline are exported toward the North especially at the beginning of the night (18 UTC to 00 UTC) with the establishment of the nocturnal low level jet. Plumes originating from different cities overlay for some hours at the coast, leading to high pollution level, because of specific disturbed meteorological conditions.