Study on the Optical–Physical Properties of Aerosol Layers in Africa Based on a Laser Satellite

Abstract

Atmospheric aerosols have important effects on the environment and human health. In this study, we analyzed the atmospheric aerosol layers’ optical and physical properties over Africa utilizing CALIPSO level 2 products from 2007 to 2019. Interannual and seasonal variations in aerosol optical parameters were studied: the lowest aerosol layer (AODL), the base height of the lowest aerosol layer (BL), the top height of the lowest aerosol layer (HL), the top height of the highest aerosol layer (HH), the volumetric depolarization ratio of the lowest aerosol layer (DRL), the color ratio of the lowest aerosol layer (CRL), the total AOD of all aerosol layers (AODT), the number of aerosol feature layers (N), the thickness of the lowest aerosol layer (TL), and the AOD proportion of the lowest aerosol layer (PAODL). The annual mean AODT was slightly higher in southern Africa than in northern Africa. HL and HH had strongly positive correlations with landform elevations. However, HL and HH were greater in northern Africa than in southern Africa from March to August. The reason could be that northern Africa is dominated by deserts with high temperatures and intense atmospheric vertical convections leading to dust layers existing in the upper air. PAODL values were lower in northern Africa (daytime: 71%; nighttime: 61%) than in southern Africa (daytime: 78%; nighttime: 69%), revealing that aerosol stratifications were more frequent in northern Africa than in southern Africa. DRL values were higher in northern Africa (daytime: 0.16; nighttime: 0.11) than in southern Africa (daytime: 0.07; nighttime: 0.05) indicating the predominance of non-spherical dust particles in northern Africa. This work can provide an important understanding of regional aerosol layers’ optical and physical properties to scientists and local environmental protection agencies.