Carbonaceous particulate matter from diesel fuel combustion was studied with Scanning Transmission X-ray Microspectroscopy, a novel synchrotron radiation-based technique, which combines X-ray absorption spectroscopy and microscopy. Single soot particles were chemically identified with a spatial resolution of better than 100 nm. Near-edge X-ray Absorption Fine Structure spectra from the carbon K-absorption edge could be assigned to specific particle regions, making it possible to distinguish graphitic carbon in the soot particles from hydrocarbons. such as residual lubricating oil and diesel fuel and their reaction products. (C) 2003 Elsevier Ltd. All rights reserved.