The main purpose of the present work was to quantify and characterize morphologically and chemically the emissions of particulate matter (PM) from a domestic pellet-fired boiler during steady-state operation for different boiler thermal inputs. The PM quantification was made with the aid of a low pressure three-stage cascade impactor and the PM characterization using SEM/EDS analysis (scanning electron microscope/energy dispersive X-ray spectrometry). The measured PM emissions varied between approximate to 1160 mg/Nm(3)@13% O-2 and approximate to 490 mg/Nm(3)@13% O-2, being the emissions mainly dominated by particles with sizes below 2.5 mu m and above 10 mu m regardless of the thermal input. The SEM analyses revealed the presence of ultra fine (<100 nm) particles, sub-micrometer and micrometer sized particles/agglomerates, and isolated spherical and irregularly shaped large particles for all boiler operating conditions examined. The ultra fine particles, formed after the soot formation process, were composed mainly of O, K. Cl, Na and S; the sub-micrometer (and micrometer) sized particles/agglomerates, formed from soot, contained mainly carbon, oxygen, Ca, Mg. K and P; and the isolated spherical and irregularly shaped large particles, released from the fuel bed during combustion. consisted mostly of carbon and oxygen with minor amounts of Ca and Mg. (C) 2011 Elsevier B.V. All rights reserved.