Climatology and dynamics of aerosol optical properties from selected AERONET sites over West Africa

Abstract

This study analyzed aerosol optical properties in West Africa, a region significantly influenced by the Sahara Desert's extensive dust emissions. Key aerosol optical characteristics, such as Aerosol Optical Depth (AOD), Angstrom exponent (α), and particle size distributions, were examined using ground-based radiometric data from five West African Aerosol Robotic Network (AERONET) sites—Cape Verde, Banizoumbou, Dakar, and Ilorin—collected between 2004 and 2009. Results indicate distinct primary and secondary AOD peaks during the dry season, with Cape Verde peaking in June. The Angstrom exponent exhibited seasonal variation, with minimum values associated with dust storms at all locations. However, Ilorin consistently showed higher α values, even during dust events, likely due to a mix of biomass burning and dust. An inverse relationship between AOD and α was observed at all sites except Ilorin. Additionally, a small fraction of α values above 1.5 were observed in Banizoumbou, Dakar, and Ilorin, with none recorded in Cape Verde. Ilorin also recorded only 21% of α values below 0.3, compared to more than 50% at other stations. Dust levels were highest in Cape Verde and lowest in Dakar, likely due to its proximity to clean maritime air. Variations in dust absorption appear to result from interactions between dust and fine-mode pollution aerosols, as well as differences in dust properties from diverse source regions.