Luo Chin-Hsiang, Lee Whei-May, Liaw Jiun-Jian
Department of Safety, Health and Environmental Engineering, Hungkuang University, Taichung 43302, Taiwan, China.
J Environ Sci (China). 2009;21(4):452-7. doi: 10.1016/s1001-0742(08)62291-3.
Diesel soot aggregates emitted from a model dynamometer and 11 on-road vehicles were segregated by a micro-orifice uniform deposit impactor (MOUDI). The elemental contents and morphological parameters of the aggregates were then examined by scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS), and combined with a fractional Brownian motion (fBm) processor. Two mode-size distributions of aggregates collected from diesel vehicles were confirmed. Mean mass concentration of 339 mg/m3 (dC/dlogdp) existed in the dominant mode (180-320 nm). A relatively high proportion of these aggregates appeared in PM1, accentuating the relevance regarding adverse health effects. Furthermore, the fBm processor directly parameterized the SEM images of fractal like aggregates and successfully quantified surface texture to extract Hurst coefficients (H) of the aggregates. For aggregates from vehicles equipped with a universal cylinder number, the H value was independent of engine operational conditions. A small H value existed in emitted aggregates from vehicles with a large number of cylinders. This study found that aggregate fractal dimension related to H was in the range of 1.641-1.775, which is in agreement with values reported by previous TEM-based experiments. According to EDS analysis, carbon content ranged in a high level of 30%-50% by weight for diesel soot aggregates. The presence of Na and Mg elements in these sampled aggregates indicated the likelihood that some engine enhancers composed of biofuel or surfactants were commonly used in on-road vehicles in Taiwan. In particular, the morphological H combined with carbon content detection can be useful for characterizing chain-like or cluster diesel soot aggregates in the atmosphere.
从一台模型测功机和11辆道路行驶车辆排放的柴油机碳烟聚集体，通过微孔均匀沉积冲击器（MOUDI）进行分离。然后，利用扫描电子显微镜与能谱仪（SEM-EDS）结合分数布朗运动（fBm）处理器，对聚集体的元素含量和形态参数进行检测。确认了从柴油车辆收集的聚集体的两种模态尺寸分布。主导模态（180 - 320纳米）中存在平均质量浓度为339毫克/立方米（dC/dlogdp）。这些聚集体中有相对较高比例出现在PM1中，突出了其对健康不利影响的相关性。此外，fBm处理器直接对分形状聚集体的SEM图像进行参数化，并成功量化表面纹理以提取聚集体的赫斯特系数（H）。对于配备通用气缸数的车辆的聚集体，H值与发动机运行条件无关。气缸数较多的车辆排放的聚集体中存在较小的H值。本研究发现，与H相关的聚集体分形维数在1.641 - 1.775范围内，这与先前基于透射电子显微镜的实验报告值一致。根据能谱分析，柴油机碳烟聚集体的碳含量按重量计在30% - 50%的高水平范围内。这些采样聚集体中钠和镁元素的存在表明，台湾道路行驶车辆中可能普遍使用了一些由生物燃料或表面活性剂组成的发动机增强剂。特别是，形态学H与碳含量检测相结合可用于表征大气中链状或簇状柴油机碳烟聚集体。
