Aerosol climatology over South Africa based on 10 years of Multiangle Imaging Spectroradiometer (MISR) data

摘要

In this paper, we present a detailed study of the spatial and seasonal aerosol climatology over South Africa (SA), based on Multiangle Imaging Spectroradiometer (MISR) data. We have used 10 years (2000–2009) of MISR monthly mean aerosol extinction (τ_(ext)), absorption (τ_a) optical depths at 558 nm, Angstrom exponents in visible (VIS; 446–672 nm) and near‐infrared (NIR; 672–866 nm) spectral bands, and the extracted spectral curvature. The study has shown that, in terms of aerosol load level spatial variation, SA can be classified into three parts: the upper, central, and lower, which illustrate high, medium, and low aerosol loadings, respectively. The results for the three parts of SA are presented in detail. The prevailing sources of aerosols are different in each part of SA. The lower part is dominated by the air mass transport from the surrounding marine environment and other SA or neighboring regions, while the central and upper parts are loaded through windablated mineral dust and local anthropogenic activities. During the biomass burning seasons (July–September), the central part of SA is more affected than the rest of SA by the biomassburning aerosols (based on τ_a, ～20% higher than the rest of SA). In alignment with the observed higher values of τ_(ext), aerosol size distributions were found to be highly variable in the upper part of SA, which is due to the high population and the industrial/mining/ agricultural activities in this area.