| Soot is an important atmospheric aerosol due to its ability to affect climate through both optical and chemical reaction pathways. Atomic force microscopy (AFM) was utilized to study the morphology, size distribution and chemical reactivity of soot and other carbonaceous materials. AFM is a powerful tool for imaging nanometer-sized particles or features under ambient or reactive conditions.; The reaction between individual carbonaceous particles and a reactive gas was monitored in real-time by following changes in particle size and shape. Specifically, the reaction between anthracene microcrystals and ozone was investigated. The most important discovery associated with this work was that the AFM probe tip dramatically affected the reaction rate with ozone. The mechanism by which the probe enhanced the reaction rate appears to be either through degradation of ozone to the more reactive oxygen atoms or through continuous creation of reactive defect sites on the microcrystal. In addition, the Kelvin effect was experimentally observed for anthracene nanocrystals at room temperature.; Highly ordered pyrolytic graphite was also examined during reaction with ozone. This system provided a stable and well-defined surface for imaging. However, a buildup of non-volatile material at the reactive sites during reaction with ozone led to unpredictable kinetics.; Soot (and carbon black) proved challenging to image with contact-mode AFM. The experimental conditions necessary to produce an appropriate soot coverage for AFM imaging were determined. The most reproducible system was an acetylene flame. The morphological characteristics of soot, under a variety of deposition conditions, were examined by AFM. Fractal aggregates were observed when sampled high in the flame, whereas, individual particles were observed when lower in the flame.; In addition to the chemical reactivity of soot, its optical properties are important for climate modeling studies. Soot extinction (i.e., absorbance and scattering) is largely dependent on particle size, morphology and the refractive index of the surrounding medium. A method combining AFM with absorbance spectroscopy was demonstrated as a means to probe particle size, morphology and extinction. In preliminary studies, the methodology was used to investigate soot on fused silica as a function of relative humidity. Based on phase imaging the soot appeared to take up water with increased humidity. The optical density of the soot films increased with increasing humidity. Both trends are consistent with previous, yet separate, studies reported in the literature. |
