Analysis of Variations in the OC/EC Ratio in PM2.5 and PM10 Aerosols during the Dry and Wet Seasons in Two West African Cities (Abidjan and Korhogo) in C？te d’Ivoire
Air quality in West Africa is strongly influenced by interactions between anthropogenic and natural emissions of particulate matter (PM). In this study, we examine variations in carbon aerosol concentrations (organic carbon (OC) and elemental carbon (EC)) during the dry and wet seasons, focusing on OC/EC ratios. This study is based on sampling from 2018 to 2020 at five urban sites in C？te d’Ivoire, including three in Abidjan (A1, A2, and A3) and two in Korhogo (K1 and K2). The results show that in Abidjan, OC/EC ratios in PM2.5 almost double between the wet season (WS) and the dry season (DS), reflecting a stronger organic contribution during the DS, while in PM10, the ratios remain stable or decrease slightly, suggesting a higher proportion of elemental carbon in coarse particles. In Korhogo, seasonal contrasts are more pronounced: at the K1 and K2 sites, OC/EC ratios increase from around 2 - 3 during the wet season to values above 5 during the dry season, with extremes at K2 where ratios in PM2.5 and PM10 double vs. WS. This variability highlights the strong influence of biomass and domestic waste combustion during the dry season, as well as marked differences between northern and southern sites in the contribution of carbonaceous species to PM2.5 and PM10 aerosols. Overall, the results highlight the value of OC/EC ratios as indicators of combustion sources and the need for seasonal monitoring in West Africa.
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