© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics

Abstract. A major fraction of fine particle matter consists of organic carbon (OC) but its origin is still inadequately known. In this study the sources of OC were investigated in the northern European urban environment in Helsinki, Fin-land. Measurements were carried out over one year and they included both filter (PM1) and online methods. From the fil-ter samples OC, elemental carbon (EC), water-soluble OC (WSOC), levoglucosan and major ions were analyzed. Filter data together with the concentrations of inorganic gases were analyzed by Positive matrix factorization (PMF) in order to find the sources of OC (and WSOC) on an annual as well as on a seasonal basis. In order to study the diurnal varia-tion of sources, OC and EC were measured by a semicontin-uous OC/EC analyzer and major ions were determined by a Particle-into-Liquid Sampler coupled to ion chromatographs