Athens is one of the European cities most burdened by particle pollution, thus the characterization of aerosol composition and sources is imperative for addressing health concerns and undertaking mitigation measures. In this study, PM10 and PM2.5 ambient samples, collected at a roadside traffic and at an urban background site, throughout an annual period, were analyzed for elemental composition and light-absorbing carbon. Positive Matrix Factorization (PMF) analysis was performed to identify sources and quantify their contribution to PM2.5 and PM10-2.5 fractions. Over 2-fold roadside enhancement of concentrations was observed for a number of vehicle-emitted and road-dust resuspended species (BC, Cu, Zn, Fe, Ca), with increments for trace elements being more notable in the coarse fraction. Source apportionment indicated that for fine particles, road traffic and sulfate-rich regional aerosols were the key contributors, with the first being dominant at the roadside site (43%) and the latter accounting for the majority (52%) of particle mass at the background location. Other fine particle sources included biomass burning -mainly during wintertime-, heavy oil combustion, mineral dust and sea salt. For coarse particles, PMF-extracted factors were associated with vehicular emissions and road dust (prevailing at the roadside site, with a combined contribution of 60%), mineral dust and sea salt (52% cumulatively at the background site). Regional contributions of secondary and natural particles were comparable at level and well correlated among sites. On the contrary, net contributions of traffic related sources recorded large concentration gradients; however, high spatial correlations were observed, especially in case of favorable wind circulations from the city center towards the background site. It appears that control of traffic related emissions, in the absence of significant point sources in the area, could have a pronounced effect at a wide spatial scale within Athens, with broad implications for the protection of public health.