Transmission electron microscopical and aerosol dynamical characterization of soot aerosols

• Published in: Journal of aerosol science Vol. 34; no. 10; pp. 1347 - 1370
• Main Authors: Wentzel, M., Gorzawski, H., Naumann, K.-H., Saathoff, H., Weinbruch, S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-10-2003
• ISSN: 0021-8502; 1879-1964
• DOI: 10.1016/S0021-8502(03)00360-4

Size, morphology and microstructure of Palas soot, Diesel soot and of Diesel soot/ammonium sulfate mixtures were studied by transmission electron microscopy (TEM). The diameter of the primary particles derived from TEM is
6.6±1.7
nm
for Palas soot and
22.6±6.0
nm
for Diesel soot. Palas soot predominantly consists of amorphous carbon. In a few cases, nanocrystalline graphite with domain sizes on the order of 1 nm were observed. Primary particles of Diesel soot always show an onion-shell structure of nanocrystalline graphite with domain sizes between 2–
3
nm
. Fractal properties of 37 Diesel soot agglomerates were determined from TEM images by two different techniques. The average fractal dimension of Diesel soot derived from TEM is 1.70±0.13. TEM further showed that the initially external mixture of Diesel soot and ammonium sulfate developed with time in a significant degree of internal mixing.
A second independent approach to determine the fractal properties of soot is based on computer simulations of the aerosol dynamics. A good reproduction of the time evolution of mass and number concentrations and of the mobility size distribution was achieved. The primary particle diameters obtained from the computer simulations (
7.3±0.8
nm
for Palas soot,
25±3
nm
for Diesel soot) are in excellent agreement with the TEM results. The fractal dimension of Diesel soot received from the COSIMA algorithm of 1.9±0.2 (overlap of primary particles was taken into consideration) is consistent with the value obtained from TEM image analysis. For Palas soot, the computer simulation yielded a fractal dimension of 2.0±0.1 (overlap was not corrected, as the overlap coefficient is not known).