Long-term (2003–2013) climatological trends and variations in aerosol optical parameters retrieved from MODIS over three stations in South Africa

The present study is aimed to analyze the spatial and temporal distributions, and trends and variations in aerosol optical properties during the last decade. For this we used the aerosol optical depth (AOD550), Ångström exponent (AE, α470–660) and fine mode fraction (FMF) products derived from the Moderate resolution Imaging Spectroradiometer (MODIS) on board Terra satellite during the period December 2003–November 2013 over three different aerosol environments in South Africa (SA). The spatial pattern of annual mean AOD is characterized with high (low) AOD in the north (south) and with a moderate AOD in the central part of SA. A decadal decrease in AOD has been noticed by performing linear trend analysis over the three stations (Pretoria, Bloemfontein and Cape Town). The seasonal and inter-annual variability of AOD values over three locations of SA showed that the higher mean AOD values occurred during spring (September) and summer (January/February) seasons, whereas the lower values were found in the late autumn/early winter periods (June). On seasonal basis, the decadal climatological variations showed a decreasing trend in different seasons except during spring. The HYSPLIT back trajectory model was used to identify airmass transport pathways originated from aerosol source regions during the dry and wet seasons.