Biomass burning in southern Africa: Individual particle characterization of atmospheric aerosols and savanna fire samples

Ambient atmospheric aerosols and savanna fire particulate emission samples from southern Africa were characterised in terms of particle classes and their number abundance by electron probe X-ray microanalysis (EPXMA). About ten particle classes were identified for each sample. The major classes were aluminosilicates and sea salts for ambient coarse (2-10 mu m equivalent aerodynamic diameter (EAD)) samples, and K-S and S-only particles for ambient fine (< 2 mu m EAD) samples. The K-S particles are one of the major products of biomass burning. The EPXMA results were found to be consistent with the results from bulk analyses on a sample by sample basis. For savanna fire fine samples, quantitative EPXMA revealed that many particles had a composition of simple salts such as KCl. Some particles had a deviating composition in the sense that more ionic species were involved in sustaining the balance between cations and anions, and they were composite or mixed salts. Because of extensive processing during the atmospheric transport, the composition of the K-S particles in the ambient samples was different from K2SO4, and such particles were enriched with S. The fine pyrogenic KCl particles and the fine sea-salt particles were much depleted in chlorine.