Individual aerosol particles from biomass burning in southern Africa: 2, Compositions and aging of inorganic particles

TLDR

Transmission electron microscopy and field‑emission scanning electron microscopy were used to examine individual aerosol particles collected during the SAFARI 2000 study, comparing their sizes, shapes, compositions, mixing states, surface coatings, and relative abundances across biomass‑burning smoke, boundary‑layer hazes, and the free troposphere, with a focus on inorganic particle aging and reactions. The study found that biomass‑burning smoke is dominated by internally mixed potassium salts and organic particles, with KCl prevailing in fresh smoke and K₂SO₄/KNO₃ increasing upon aging due to reactions with sulfur and nitrogen species, soot is more abundant in flaming grass fires, and the high levels of organics and soluble salts enhance hygroscopicity, making these particles key contributors to regional haze and cloud condensation nuclei.

Abstract

Individual aerosol particles collected over southern Africa during the SAFARI 2000 field study were studied using transmission electron microscopy and field‐emission scanning electron microscopy. The sizes, shapes, compositions, mixing states, surface coatings, and relative abundances of aerosol particles from biomass burning, in boundary layer hazes, and in the free troposphere were compared, with emphasis on aging and reactions of inorganic smoke particles. Potassium salts and organic particles were the predominant species in the smoke, and most were internally mixed. More KCl particles occur in young smoke, whereas more K 2 SO 4 and KNO 3 particles were present in aged smoke. This change indicates that with the aging of the smoke, KCl particles from the fires were converted to K 2 SO 4 and KNO 3 through reactions with sulfur‐ and nitrogen‐bearing species from biomass burning as well as other sources. More soot was present in smoke from flaming grass fires than bush and wood fires, probably due to the predominance of flaming combustion in grass fires. The high abundance of organic particles and soluble salts can affect the hygroscopic properties of biomass‐burning aerosols and therefore influence their role as cloud condensation nuclei. Particles from biomass burning were important constituents of the regional hazes.