Located in the Mediterranean Basin and close to Marseille (France), Fos-sur-Mer is situated in the vicinity of industrial harbor and agricultural lands. Its location makes it prone to mixed pollution contributions, combining the influence of residential, industrial, agricultural, maritime road and traffic sources. For this study, the origins of carbonaceous particles sampled over several months are investigated by a coupled approach based on analyses of radiocarbon (14C), elemental to total carbon ratio (EC/TC) and various molecular tracers (levoglucosan, methoxyphenols, malic and glyceric acids), giving information about their background origins. Accelerator mass spectrometry with a gas ion source give the opportunity to quantify the fossil and non-fossil fractions for each individual sample, avoiding to pool them. Analyzing 14C in micro-samples (down to a few μg of carbon) complements the approach based on chemical tracers, which are useful to identify sources, but insufficient to quantify accurately the modern and fossil carbon fractions.The measurements in about 30 samples collected during summer and fall/winter 2013, allow the detection of a strong seasonality of the pollution: the fall/winter PM2.5 fraction concentration equals to three times the summer concentration and we observe a significant fluctuation of the relative contributions of fossil and non-fossil fractions (fNF is ≈ 0.83 for fall/winter samples and ≈0.59 for summer samples).Significant correlations between 14C, levoglucosan and different methoxyphenols, allow the identification and quantification of a major influence of biomass burning emissions during fall and winter. Biomass burning organic carbon (OCBB) and elemental carbon (ECBB) contribute to 45% and 8% of the TC, respectively, whereas their total contribution is only 3% in summer samples.Biogenic emissions from the vegetation are the main sources of carbon during summer (≈57%). Significant correlations between summer OCbio and malic acid and DL glyceric acid suggest a secondary origin for this fraction.The total fossil carbon concentration (ECF and OCF) from vehicular, shipping and industrial sources is constant throughout the year, which is compatible with intense road and maritime traffics and industrial activity during both seasons.Overall, our study based on 14C and molecular tracers illustrates the power of a coupled approach in order to both identify and quantify biomass burning, biogenic, traffic and industrial sources of carbonaceous aerosols, forming a complex mix of background PM origins in a typical industrious harbor of the Mediterranean region.