Abstract
Abstract. Carbon monoxide, CO, and fine atmospheric particulate matter, PM2.5, 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 PM2.5 concentrations is important. The contribution of desert dust PM2.5 concentration decreases from ∼ 38 % in May to ∼ 5 % in July. The contribution of biomass burning PM2.5 concentration from Central Africa increases from ∼ 10 % in May to ∼ 52 % in July. The anthropogenic contribution is ∼ 30 % for CO and ∼ 10 % for PM2.5 during the whole period. 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 PM2.5 and CO concentrations are higher than in May or July over the Guinean coastal region. Air mass dynamics concentrate pollutants emitted in the Sahel due to a meridional atmospheric cell. Moreover, a part of the pollution emitted remotely at the coast is transported and accumulated over the Sahel. Focusing 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 (18:00 to 00:00 UTC) with the establishment of the nocturnal low level jet. Plumes originating from different cities are mixed for some hours at the coast, leading to high pollution concentration, because of specific disturbed meteorological conditions.
Highlights
The interaction between air pollution and climate in major population centers is a challenging field of research (Baklanov et al, 2016)
It is read and interpolated hourly by Weather Research and Forecasting (WRF) using low-frequency spectral nudging above the planetary boundary layer (PBL) in order to enable the PBL variability to be resolved by WRF
These are similar but not equivalent patterns to those presented in Sect. 3.1 averaged over the whole of West Africa
Summary
The interaction between air pollution and climate in major population centers is a challenging field of research (Baklanov et al, 2016). At a regional scale (a few hundred kilometers), the monsoon wind from the south meets the harmattan wind from the north, forming the Intertropical Discontinuity at ground level (Flamant et al, 2007; Cuesta et al, 2009; Karam et al, 2009; Pospichal et al, 2010), and leading to a complex vertical structure (Haywood et al, 2008; Lafore et al, 2011) Between these two scales, an additional meridional atmospheric cell is suspected in the low atmosphere, enhancing convergence at the coast (LeducLeballeur et al, 2013).
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