Aerosol source apportionment in southern Africa

Abstract

South Africa, and especially the Highveld region, contributes significantly to the atmospheric aerosol loading over southern Africa. South Africa has recognised the importance of localised air quality and its impact on human health with the declaration of the Vaal Triangle, Highveld and Waterberg-Bojanala regions as Air Quality Priority Areas. In this thesis, the composition and sources of the aerosol loading at identified sites in each of these regions, namely, Lephalale (in the Waterberg-Bojanala), Kwazamokhule and Embalenhle (in the Highveld) and Zamdela (in the Vaal Triangle) have been examined. Fine and coarse aerosol samples were collected at each selected site during summer and winter spanning the period 2012 to 2017. The chemical and elemental composition of aerosol samples collected at each site has been evaluated and apportioned to contributing sources using three source apportionment methods, namely, Principal Component Analysis (PCA), Positive Matrix Factorisation (PMF) and Chemical Mass Balance (CMB) receptor modelling. Using these methods, it has been shown that soil dust (natural and anthropogenic), secondary aerosols, domestic combustion (coal combustion and waste burning) and wood and biomass burning contribute to the fine and coarse aerosol loading in each region. Motor vehicles and industrial activities were also identified in the Highveld and Vaal Triangle regions. Overall, soil dust and secondary aerosols are the main contributing sources in both aerosol size fractions and as such, measures to mitigate particulate air pollution in South Africa should consider these key sources. Given the ease of application and limitations associated with each of the three source apportionment methods, the use of PCA as an initial screening tool, followed by the application of PMF, is the recommended approach for aerosol source apportionment studies in South Africa.