In this study, the microstructure and oxidation behaviour of soot from the raw exhaust of a Euro IV test heavy duty (HD) diesel engine are investigated and compared to that of spark-discharge soot and hexabenzocoronene (HBC, C42H18). We find a microstructure-controlled reactivity towards oxidation of all three samples in 5% O-2 in N-2. The spark-discharge soot with its fine primary particles and fullerenoid structure has an onset temperature of 423 K for combustion, while the HBC with its well-ordered crystallites has a high onset temperature of 773 K. Due to an improved combustion process in the Euro IV HD diesel engine, the emitted soot consists of more fullerenoid- or onion-like particles agglomerated in a chain-like secondary structure. The onset temperature of the Euro IV HD engine soot combustion is 573 K. Oxidation of the three samples produces only CO2 and H2O. The different H2O production profiles can be assigned to the functionalised surface of the samples and depend on the soot structure and preparation route. (C) 2004 Elsevier B.V. All rights reserved.