Elemental and organic carbon in the urban environment of Athens. Seasonal and diurnal variations and estimates of secondary organic carbon

► Long term measurements of EC-OC, with a high time resolution, are reported for the first time in Athens. ► Mean OC concentrations ranked in the upper echelon of levels observed in Europe. ► Seasonal and diurnal patterns indicate the importance of SOA. ► Hourly variations of SOA are estimated for the first time in Athens. ► The conservative average estimate for the secondary component of OC, at an urban location, is 25%.