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 th eir number abundance by electron probe X-ray microanalysis (EPXMA). About t en particle classes were identified for each sample. The major classes were aluminosilicates and sea salts for ambient coarse (2-10 mu m equivalent ae rodynamic 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 produc ts of biomass burning. The EPXMA results were found to be consistent with t he results from bulk analyses on a sample by sample basis. For savanna fire fine samples, quantitative EPXMA revealed that many particles had a compos ition of simple salts such as KCl. Some particles had a deviating compositi on in the sense that more ionic species were involved in sustaining the bal ance between cations and anions, and they were composite or mixed salts. Be cause of extensive processing during the atmospheric transport, the composi tion 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 a nd the fine sea-salt particles were much depleted in chlorine.