The influence of temperature on the properties of the soot formed from C2H2 pyrolysis has been studied. Pyrolysis experiments were carried out in a quartz reactor at 1000-1200 degrees C, for an inlet C2H2 concentration of 15,000 ppmv. Outlet gases were analysed by gas chromatography and the amount of soot produced measured. The soot samples formed were further characterized using elemental analysis, BET surface area, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Raman spectroscopy. The soot reactivity towards O-2 and NO was studied. Results show that formation temperature is a key parameter in the properties and reactivities of the soot samples formed. The higher the temperature the less reactive the soot, and structural properties support these results. (c) 2006 Elsevier B.V. All rights reserved.