Spectro-microscopic Characterization of Carbonaceous Particulates

Mary Gilles Lawrence Berkeley National Laboratory
Ryan Moffet University of the Pacific
Shruti Prakash Lawrence Berkeley National Laboratory
Alexander Laskin Pacific Northwest National Laboratory

Category: Aerosol Properties

Working Group: Aerosol Life Cycle

Carbonaceous particles formed by combustion account for a large fraction of light-absorbing aerosols. Understanding and characterizing the diversity of particulate matter produced from fossil fuel and biomass burn combustion is important for modeling radiative properties of the atmosphere. In recent years we have combined a variety of micro-spectroscopic techniques to probe carbonaceous particulates: specifically, scanning transmission x-ray microscopy, capable of performing near-edge x-ray fine-structure micro-spectroscopy, (STXM/NEXAFS), and computer-controlled scanning electron microscopy coupled with an energy-dispersive x-ray analyzer (CCSEM/EDX) for elemental analysis. STXM/NEXAFS is used to explore the diversity of bonding, carbon sp2 hybridization, and C/O atomic ratios of light-absorbing particulates. It has also been used to illustrate chemical and morphological differences in bonding between fractal soots and aged biomass burn particulates (tar balls). For the tar balls, examination of the carbonyl intensity as a function of particle size indicates the presence of a thin oxygenated interface layer. Additionally, in studies on controlled burns of biomass fuels, we observed a striking range in particulate matter produced. Current studies examine changes in carbon bonding during charring that could influence the determination of elemental carbon/organic carbon. These studies have formed the base for recent work on physical and chemical transformations of collected particles aged in the outflow from Mexico City. Such studies have the potential to improve our understanding of the composition of organic particles and their environmental processing.

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