Daily PM2.5 concentrations and composition were monitored at an urban site at 14 m above ground level, at the National Technical University of Athens campus from February to December 2010. Total sulfur, crustal origin elements and elements of a major crustal component (Al, Si, Fe, Ca, K, Mg, Ti) trace elements (Mn, V, Pb, Cu, Zn, Ni) and water soluble ions (Cl–, NO3–, SO42–, Na+, K+, NH4+, Ca2+, Mg2+) were determined. Carbonaceous compounds were determined for a period of one month. Sulfur (sulfates) and carbonaceous material were the most abundant constituents (35% and 30% respectively). Ionic balance calculations revealed a cation deficit in PM2.5 attributed to H+ associated with sulfates. The concentrations of the elements of crustal origin presented abrupt increases during Saharan dust transport events. Mass closure was attempted considering Secondary Inorganic Aerosol (SIA), Particulate Organic Matter (POM), Elemental Carbon (EC), Dust, Mineral Anthropogenic Component (MIN) and Sea Salt (SS). The sum of these components accounted for about 75% of the measured PM2.5 concentrations. SIA and carbonaceous material (OM + EC) contributed almost equally for about 30% in the PM2.5 mass, and while the dust contribution was significant during dust transport events, it was only about 5% in absence of such events. The contribution of sea salt was calculated to be about 4%.