This article describes an experimental investigation of the oxidation behavior of particulate matter (PM) sampled with the aid of a rapid dilution probe from a number of measurement positions located in the near the burner region of a domestic wood pellet-fired boiler. Morphology and chemical composition of the collected PM samples were examined in a scanning electron microscope equipped with an energy dispersive X-ray spectroscopy detector. To evaluate the oxidative reactivities of the PM samples, experiments were performed in a quartz reactor with an inlet oxygen concentration of 500 ppm in a nitrogen flow, a temperature of 900 degrees C, and a flow rate of 1000 mL/min (STP). Results obtained from the oxidation tests indicated that the PM samples collected from locations near the visible flame boundary were significantly less reactive towards O-2 than those sampled from locations along the burner axis. This fact may be due to the higher temperatures occurring near the visible flame boundary, resulting in PM samples with a higher degree of material organization and a lower availability of active sites. (C) 2013 Elsevier B.V. All rights reserved.