Soot varies, in physical structure and chemical composition, as dependent upon its source, primarily diesel engines, combustors or power plants. Prior studies have shown the near atomic level structure of soot to be dependent upon the source via quantification of physical structure parameters extracted from HRTEM images. In principle this permits identification of the soot source and its contribution to any particular receptor site. Yet many structural aspects are subtle and the variable chemistry of the particles remains unaddressed. This project will investigate the process of transient laser processing to highlight compositional and structural differences, thereby distinctively and uniquely identifying the source of the soot. The significance of pulsed laser processing is that the material transforms to yield distinctive patterns, dependent upon the combination of initial chemistry and structure. The goal is then to develop the laser-based processing as an analytical tool and identify the process conditions and operational parameters for optimal transformation. Specific objectives directed towards achieving this goal include identifying laser operational parameters, defining dependence upon initial structure and composition, demonstrating differentiation between soot from different sources and quantifying the structural changes statistically.
Soot is routinely emitted from heavy-duty trucks, power plants and even jet aircraft such as upon takeoff. Soot is the byproduct of incomplete combustion. Its formation reflects combustion inefficiency and its release imposes health risks and environmental concerns. According to the EPA, soot from anthropogenic sources is responsible for many negative health consequences including asthma, heart arrhythmias and even hospitalizations. New findings show soot may be contributing to climate changes happening near the North Pole, such as accelerating melting of sea ice and snow and changing atmospheric temperatures. Although black carbon is hydrophobic (water hating), chemical and physical changes occurring at its surface can cause it to become hydrophilic (waer loving). Such changes determine soot's contribution to cloud formation, its susceptibility to atmospheric washout and its participation in atmospheric heterogeneous reactions. All such processes significantly impact the atmospheric radiative balance. Recent estimates place black carbon radiative forcing as nearly half that attributed CO2. Therein tracking soot dispersion and source identification is a starting point to address these issues.
