| Individual aerosol particles from the North Atlantic Ocean and southern Africa were studied using transmission electron microscopy and field-emission scanning electron microscopy, with emphasis on their sizes, morphologies, compositions, species, mixing states, and relative abundances. This study provides a detailed characterization of aerosols from different sources and insight into their reactions and evolution.; Major particle types from the North Atlantic consisted of chloride, sulfate, and nitrate of sodium, ammonium sulfate, soot, flyash, silica, and iron oxide. Aerosols from two sampling sites showed dramatic differences in abundances of distinct particle types. At Sagres on the coast of Portugal, most sea salt particles were partly or completely depleted in chlorine and enriched in sulfur, nitrogen, or both. In contrast, at Punta del Hidalgo on the Canary Islands, only during polluted periods were sea salt particles partly reacted to sulfate and nitrate. Heterogeneous oxidation of sulfur dioxide in deliquescent sea salt, reactions with nitric acid, and cloud processing may be the major mechanisms of sea salt reactions. Concentrations of other pollutants including soot, flyash, and ammonium sulfate were higher at Sagres than at Punta del Hidalgo. These differences suggested the great impact of European pollution on marine aerosols and the dilution, rapid reaction, and exhaustion of reactive pollutants as they were transported to the open ocean.; Individual aerosols from biomass burning and regional hazes in southern Africa were also characterized and the aging of smoke particles was investigated. Smoke aerosols mainly included potassium salts, tar balls, organic particles, soot, and calcium-bearing particles. Soot was most abundant in smoke from grass fires, probably owing to the predominance of flaming combustion. More potassium chloride particles occurred in young smoke, whereas more potassium sulfate and nitrate particles were in aged smoke. This change indicates the conversion of potassium salts through reactions of potassium chloride with sulfur- and nitrogen-bearing species as the smoke aged. Owing to the different hygroscopic properties of these potassium salts, the transformation suggests that the high cloud-nucleating efficiency of fresh smoke would diminish with age. Smoke particles were common in the regional hazes, suggesting that biomass burning contributed to the haze formation. |
