Spatio-temporal Variations and Trends of Aerosol Optical Depth over Guinea, Guinea-Bissau, and Senegal Based on VIIRS Satellite Validated with AERONET (2012–2024)

This study aimed at using Visible Infrared Imaging Radiometer (VIIR) to investigating the spatial and temporal variation of aerosols over West African sub- region and its deriving factors play a vital role for assessing the impacts of aerosols on air quality, health and environment. Aerosol optical depth is a key variable and important indicator as it measures the aerosol loading in the atmosphere. This study examined the spatiotemporal variations and trends in aerosol optical depth (AOD) at 550nm wavelength over West African sub-region Guinea (GU), Guinea Bissau (GB) and Senegal (SE) from 2012 to 2024.The daily AOD data were retrieved from Visible Infrared Imaging radiometer (VIIR) satellite to evaluate monthly, seasonal, annual spatiotemporal variation and aerosol modal characteristics and the AERONET data were used for validation. The results shows that, GU, GB and SE has the highest AOD value in spring (0.54) (0.55) (0.56) and the least in autumn (0.30) (0.31) (0.33) respectively. The Annual mean AOD fluctuate considerably with the higher AOD value are (0.47) & (0.45) in 2015 and (0.48) in 2017, the least AOD value are (0.36) (0.37) and (0.38) in 2013 for GU, SE and GB respectively. Additionally, month of June exhibit a higher AOD value of (0.84) and least in January (0.25) for SE, February (0.58) and August (0.25) for GU and January (0.67) and October (0.27) for GB respectively. Scatter plot of AOD and AE were used to characterized the aerosols modal, Biomass burning (BB),Sea salt(SS), Saharan dust (SD) and Vehicular emission(VE).GU (fine mode: 1.2-1.8, coarse mode: 0.51-1.2, Mixed mode: 0-0.51), GB (fine mode: 1.1-1.8, coarse mode: 0.-0.5, Mixed mode: 0.5-1.1), and SE ((fine mode: 1.0-1.8, coarse mode: 0.3-1.0, Mixed mode: 0-0.3). These findings underscore the need for rigorous air quality regulations and emission control measures in West Africa coastal region.