Fractal Dimension and Chemical Composition of Suspended Particulates Emitted from Pollution Sources

In recent years, the approaches to determine the pollution source contribution are primarily sampling the pollution and the receptor points. Traditionally, we can determine the pollution source contribution after sampling by means of the physical and chemical analysis. However, these approaches are complicated and difficult. In light of this, we chose the diesel car and steel-making pollution source to conduct the research. Size, morphology, hurst coefficient, fractal dimension, and chemical elements of the single particle were investigated by scanning electron microscopy(SEM), energy-dispersive spectrometer(EDS) and fractal model analysis.
A lot of aggregates were observed in the SEM micrographs. The result indicated that the soot particles emitting from the elevent diesel cars are similar in the morphology. These aggregates are formed by condensation or aggregation of primary particles. Fractal properties of diesel soot aggregates were determined by fractal model. The hurst coeffricent of diesel soot aggregates in the 105 magnification images is about 0.225~0.359; comparing to standard samples (0.194~0.374), the result locates in a reasonable range. As to the comparison with the hurst coefficient of soot aggregates from different diesel cars, we found that with the increases of exhaust, the hurst coefficient would be lowered. In contrast, with the increases of the age of the diesel car, the hurst coefficient would be enhanced. Moreover, with the increases of the mileage of the diesel car, it was shown that the hurst coefficient did not have a significant difference.
In addition, the morphology of the particles emitting from the steel-making were complicated, and they appeared in the form of mineralogy. With the same steps, the hurst coefficient of the steel-making aggregates which we established fell in about 0.469~0.633 (2×104 magnification), and the fractal dimension was about 1.449.
The chemical elements of the single particle were analyzed by EDS. We found that with the larger size of the diesel soot aggregates, the carbon contents were high. This result indicated that the carbon was the major element in all of the chemical elements. Besides, we also discovered other heavy metal elements, such as Fe, Zn, Mn and Cr. The steel-making aggregates contained many elements(C, Na, S, Fe, Zn, Mn, Mg, Cr, Al, etc). According to the classification of weight percentage, the aggregates are mainly composed of Fe and Zn.
The contribution of this work could set up the characteristic of the single particles of two different pollution source, and it could be a database of comparison.

Keyword: single particle, diesel car, steel-making, fractal dimension, chemical analysis