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Journal article

Characterization of light-absorbing carbon particles at three altitudes in East Asian outflow by transmission electron microscopy

Zhu J, Crozier P, Anderson J ...see all

Atmospheric Chemistry and Physics, vol. 13, issue 13 (2013) pp. 6359-6371

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Abstract

The morphology, microstructure, and composition of the submicron fraction of individual light-absorbing car-bon (LAC) particles collected by research aircraft during the ACE-Asia (Asian Pacific Regional Aerosol Characterization Experiment) project above the Yellow Sea at altitudes of 120, 450 and 1500 m are investigated by transmission electron mi-croscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Two types of carbonaceous particles, small spherule soot with graphitic spherules and amorphous carbonaceous spheres (brown carbon), are found at all altitudes in high concentration. For soot particles, emphasis of the study is on the component subparticles (spherules). The nanoscopic structures of the small spherule soot show no significant dif-ference at three altitudes although the size distribution of pri-mary spherules showed that 70 % of the total volume lies in the ranges 30–50, 50–85 and 30–50 nm, respectively. For the amorphous carbonaceous spheres, 70 % of the total volume from three altitudes lies in the range 200–350, 160–470 and 150–320 nm, respectively. Within the size fraction studied (submicron, with most particles in the range 50 to 500 nm) the number concentration ratios of the amorphous carbona-ceous spheres to primary spherules in soot at altitudes of 120, 450 and 1500 m are about 1, 1.5 and 10, respectively and their volume ratios are about 260, 50 and 1400. Lower rela-tive concentrations of large spherule soot with intermediate graphitic structure were observed at 120 m. Also, low rela-tive number concentrations of carbon cenospheres were ob-served at 120 and 1500 m. A key result of the study is that in vertically stratified outflow from East Asia, the character of LAC may have strong variance with altitude thus resulting in optical characteristics that vary with altitude. Also, apparent " aging " of LAC deduced from samples at multiple ground stations may instead reflect differences in the original carbon aerosols.

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