This study has used TOMS AI as well as the reanalysis dataset of thirty-four years (1979-2012) to investigate the influence of atmospheric circulation on dust transport during the Harmattan period in West Africa, using Aerosol Index (AI) data, obtained from various satellite sensors. Changes in Inter-Tropical Discontinuity (ITD), Sea Surface Temperature (SST) over the Gulf of Guinea, and North Atlantic Oscillation (NAO) during Harmattan period (November-March) have been analyzed on daily basis with Harmattan dust mobilization as well as atmospheric circulation pattern being evaluated via a kernel density estimate that shows the relation between the two variables. The study has found out that strong north-easterly (NE) trade winds were over most of the Sahelian region of West Africa during the winter months with the maximum wind speed reaching 8.61 m/s in January. The strength of NE winds determines the extent of dust transport to the coast of Gulf of Guinea during winter. This study has also confirmed that the occurrence of the Harmattan chiefly depends on SST in Atlantic Ocean as well as ITD position, not to mention the strength of low level winds. However, it has been noted that NAO has limited effects on dust mobilization in West Africa, in shear contrast to North Africa where NAO is a strong factor in dust mobilization.

This study utilizes a decade long (2005-2014) monthly data of Total Column Tropospheric Ozone (TCTO) in Dubson units to evaluate the spatial and temporal trend of LAO over some major cities of West Africa, namely Lagos, Accra, Niamey, Abuja, Bamako, Dakar, Agadez, Conakry, Kano, and Ouagadougou which are either capital cites or major commercial hubs, where the population ranges from 0.09 million (Agadez, Niger) to over 9 million (Kano and Lagos, Nigeria). The mean (long term average) of TCTO in Lagos (Nigeria) was 34.4±0.6 DU (α=5%) for the entire period, being the highest in all major cities of this study. The lowest TCTO, 30.4±0.5 DU (α=5%), occurred in Bamako (Mali). It was also observed that the concentrations of TCTO vary seasonally. The seasonal changes in TCTO was investigated by categorizing months of the year to very dry months of December, January, and February (DJF), onset of rainy season months of March, April, and May (MAM), wet season months of June, July, and August (JJA), and end of rainy season months of September, October, and November (SON). Seasonal mean of TCTO is higher in all cities, close to the coast during DJF, and cities, north of latitude 12o N, during MAM, compared to rest of the seasons. Elevated TCTO concentrations can be attributed to transport mixing, due to the flow direction of well-known wind regime over the study area. This was established from the analysis of correlation coefficient between the mean of zonal, meridional winds, vertical wind speeds and divergence, and TCTO over region.

Marine bivalves are bioindicators of coastal environmental pollution, integrating monitoring programs worldwide. Nonetheless, the choice of particular species as an indicator requires validation, achieved by understanding the differences in element concentrations among and within species. The present study compares the chemical composition of whole body soft tissues of four common bivalve species from the Bijagós Archipelago, a pristine region of West Africa. Significant differences were recorded in the concentrations of various elements among studied species, which likely arise from species-specific uptake and bioaccumulation processes. Overall, there was a segregation between a group including the bloody cockle Senilia senilis and oyster Crassostrea tulipa (with high Cd and Zn concentrations) versus the two other species, Austromacoma nymphalis (with low Cu and high Mn, Se, Hg, Pb concentrations) and Diplodonta spp. (with high values of Cu, Al, Fe, V, Cr, Hg, Pb). C. tulipa was sampled in two different substrates (rock beds and mangrove roots), and the two groups revealed different chemical profiles, with significantly higher concentrations of P, Si, Zn and Cr and lower Cu in specimens fixed in mangrove roots. These results strongly suggest the influence of small-scale environmental variability on the accumulation of particular elements. We found extremely high Cd concentrations in S. senilis (27.1 ± 7.53 μg g⁻¹ DW) and identified C. tulipa as another high Cd-accumulating species (ca. 10 μg g⁻¹ DW). Our results suggest a detoxifying mechanism linked with the presence of Se to reduce the potential toxic effects of Cd in these two species. Cadmium concentrations reported for some bivalve species in this area largely exceed the maximum values proposed by the European Union, emphasizing the need for a regular contamination assessment.

This work evaluates the mercury (Hg) contamination status (sediments and biota) of the Bijagós archipelago, off the coast of Guinea-Bissau. Sediments exhibited very low concentrations (<1–12ngg−1), pointing to negligible sources of anthropogenic Hg in the region. Nevertheless, Hg is well correlated to the fine fraction, aluminium, and loss on ignition, indicating the effect of grain size and organic matter content on the presence of Hg in sediments. Mercury in the bivalves Tagelus adansoni and Senilia senilis did not vary considerably among sites, ranging within narrow intervals (0.09–0.12 and 0.12–0.14μgg−1 (dry weight), respectively). Divergent substrate preferences/feeding tactics may justify slight differences between species. The value 11ngg−1 is proposed as the sediment background concentration for this West-African coastal region, and concentrations within the interval 8–10ngg−1 (wet weight) may be considered as reference range for S. senilis and T. adansoni in future monitoring studies.

The aim of this study was to examine the temporal and spatial total column ozone distribution in West Africa using Total Ozone Mapping spectrometer (TOMS) daily data for five years between 2001 and 2005 in fifteen locations. In this study, certain significant observations emerged: weather activity particularly the rainfall producing mechanism (dynamic of the wind systems) was responsible for about 62% ozone distribution in the region. Ozone maximum and minimum concentrations over all the stations were 305 DU and 232 DU respectively producing an average range of 73 DU (only about 27.03% of the mean value). Ozone has a seasonal distribution with minimum occurring during the dry season and maximum occurring during the wet season. A decreasing rate of about –0.6 DU/year was found for the region. Interannual ozone characteristics revealed an oscillating feature similar to Quasi – biennial Oscillation (QBO) footprints which indicated the importance of stratosphere – troposphere exchange to ozone distribution in the region. Furthermore, lag of about one or two months occurs between south (lower latitude) and north (higher latitude) monthly ozone maximums.