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Volume 11, No. 1, February 2011, Pages 1-12 PDF(917 KB)  
doi: 10.4209/aaqr.2010.07.0061   

Characteristics of Atmospheric Elemental Carbon (Char and Soot) in Ultrafine and Fine Particles in a Roadside Environment, Japan

Kyung Hwan Kim1, Kazuhiko Sekiguchi1,2, Shinji Kudo1, Kazuhiko Sakamoto1,2

1 Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
2 Institute for Environmental Science and Technology, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan




Atmospheric carbonaceous components, particularly char and soot in ultrafine particles (UFPs; Dp < 0.1 μm) and fine particles (FPs; Dp < 2.5 μm), were measured four times during one year in Saitama City, Japan, to observe the concentrations of elemental carbon (EC) and the relationship between the EC concentrations in UFPs and FPs, and to examine the possible emission sources of char and soot that constitute UFPs and FPs in a roadside environment. It was found that EC accounts for 33–37% of total carbon (TC) in FPs, whereas EC accounts for 12–20% of TC in UFPs. Both char-EC and soot-EC account for similar proportions of the total EC concentration in UFPs, while soot-EC accounts for only a small amount of the total EC in FPs. Positive and negative correlations between OC and soot-EC were observed for UFPs and FPs, respectively. The observed positive correlation in the case of UFPs possibly reflects the compactness (high density) of UFPs coated with condensed material, such as unburned fuel or lubricating oil emitted by motor vehicles, whereas the negative correlation in the case of FPs possibly indicates that whether or not the spaces between primary soot particles in FPs can be filled depends on the engine load of diesel vehicles operated near the sampling site. The positive and negative correlations were stronger for UFPs (r2 = 0.69, n = 29, p < 0.001) and FPs (r2 = –0.62, n = 29, p < 0.001) when the data collected at wind speeds greater than 2.5 m/s were excluded. The different morphological characteristics of the particles observed by transmission electron microscopy also support the observed correlations between OC and soot-EC. The possible emission of char or char-like particles from motor vehicles was shown and discussed in this study.



Keywords: Black carbon (BC); Ultrafine particles; Char-EC; Soot-EC; Diesel exhausts.



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