The microstructure of soot-like carbons is correlated with their reactivity toward combustion. The focus of this study is on Euro IV heavy duty diesel engine soot. Additionally, two soot samples providing lower and larger particle sizes as their most striking property are taken as references. The effect of NO2 addition to the O-2-containing gas feed is investigated. It is found that NO2 accelerates the oxidation of soot in the low-temperature region (250-400 degrees C) due to an increased surface functionalization with oxygen groups and a subsequent decomposition thereof. Accordingly, initially highly functionalized soot is less susceptible to this effect. The apparent activation energy of combustion is remarkably lowered in the presence of NO2. It is found that the total reactivity correlates with microstructural features such as surface functionalization, size and curvature of basic structural units, stack height, and particle diameter. (c) 2012 Elsevier B.V. All rights reserved.