Abstract View
Laser Derivatized Black Carbon Nanostructure: Characterization and Tests for Identifying Emission Sources
Madhu Singh, RANDY VANDER WAL, Penn State University
Abstract Number: 269
Working Group: Source Apportionment
Abstract
Source identification is important to pollution receptor models that require knowledge of source contributions at receptor sites. In this study black carbon samples from known sources are imaged via transmission electron microscopy (TEM) before and after laser heat treatment. Image processing algorithms quantify nanostructure characteristics including fringe length, fringe tortuosity, fringe spacing, stacking and curvature for nascent and laser heated black carbon. These metrics collectively comprise the identification marker or “fingerprint” for black carbon particulate. Unknown samples can then be compared against information available from existing samples to identify its source or have a close estimate of what the source may be, both qualitatively and quantitatively. Quantitative comparison for identification uses statistical analyses. By this approach, laser derivatization uses the changed black carbon nanostructure post laser heat treatment to identify the particulate source.
Soot source identification by analysis of laser-annealed nanostructure is premised on black carbon particulate from different combustion sources differing in nascent nanostructure. Combustion conditions of temperature, pressure, fuel, fuel-air-ratio, fuel-air mixing are specific to each emission source and differ between sources. Thus, black carbon particulate originating from different sources will vary in chemical composition and physical nanostructure reflecting its formation conditions. With distinct nanostructure TEM imaging followed by application of image analysis algorithms can quantify nanostructure parameters. When sufficiently distinct, contrasting nanostructure can identify the black carbon origin. In black carbon where nanostructure is poorly contrasted, it can be magnified by laser annealing (derivatization) to enhance lamellae recognition and quantification. Additionally, subtle differences in chemical composition (e.g. bonding, elemental content) between black carbons also contribute to the annealing trajectory and differentiation. The term derivatization is applied stemming from analytical chemistry where derivatization is a process by which a compound is chemically changed to improve recognition or detectability. Laser derivatization is used here in a similar manner to enhance differences in black carbon nanostructure and chemistry upon laser heating. In this talk laser annealing results for differentiating black carbons from varied sources; turbo-combustor, diesel engine, wildfire along with reference carbon blacks will be shown – highlighting initial differences in chemistry and improving nanostructure recognition and differentiation.