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Abstract: The carbon-to-oxygen ratios and graphitic nature of a range of black carbon standard reference materials (BC SRMs), high molecular mass humic-like substances (HULIS) and atmospheric particles are examined using scanning transmission X-ray microscopy (STXM) coupled with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Using STXM/NEXAFS, individual particles with diameter are studied, and the diversity of atmospheric particles collected during a variety of field missions is assessed. Applying a semi-quantitative peak fitting method to the NEXAFS spectra enables a comparison of BC SRMs and HULIS to particles originating from anthropogenic combustion and biomass burns, thus allowing determination of these materials suitability for representing atmospheric particles. Anthropogenic combustion and biomass burn particles can be distinguished from one another using both chemical bonding and structural ordering information. While anthropogenic combustion particles are characterized by a high proportion of aromatic-C, the presence of benzoquinone and are highly structurally ordered, biomass burn particles exhibit lower structural ordering, a smaller proportion of aromatic-C and contain a much higher proportion of oxygenated functional groups. [Copyright &y& Elsevier]