Athens is one of the European cities most burdened by particle pollution; thus, characterizing the 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 their elemental composition and light-absorbing carbon. Positive Matrix Factorization (PMF) analysis was performed to identify sources and quantify their contributions to the PM2.5 and PM10–2.5 fractions. Above a two-fold roadside enhancement of concentrations was observed for a number of vehicle-emitted and road-dust resuspended species (BC, Cu, Zn, Fe and Ca), with increments for trace elements being more notable in the coarse fraction. Source apportionment indicated that road traffic and sulfate-rich regional aerosols were the key contributors to the fine particles, with the former being dominant at the roadside site (43%) and the latter accounting for the majority (52%) of the 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, the 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 in level and well correlated among the sites. On the contrary, the net contributions from traffic related sources exhibited large concentration gradients; however, high spatial correlations were observed, especially in cases with favorable wind circulations from the city center towards the background site. It appears that controlling traffic related emissions, in the absence of significant point sources in the area, could have a pronounced effect on a wide spatial scale within Athens, with broad implications for the protection of public health.