Three year study of tropospheric ozone with back trajectories at a metropolitan and a medium scale urban area in Greece

Three years of hourly O-3 concentration measurements from a metropolitan and a medium scale urban area in Greece: Athens and Ioannina respectively, were analyzed in conjunction with hourly wind speed/direction data and air mass trajectories, aiming to reveal local and regional contributions respectively. Conditional Probability Function was used to indicate associations among distinct wind directions and extreme O-3 episodes. Backward trajectory clusters were elaborated by Potential Source Contribution Function on a grid of a 0.5 degrees x 0.5 degrees resolution, in order to localize potential exogenous sources of O-3 and its precursors. In Athens, an increased likelihood of extreme O-3 events at the Northern suburbs was associated with the influence of SSW-SW sea breeze from Saronikos Gulf, due to O-3 transportation from the city center. In Ioannina, the impacts of O-3 conveyance from the city center to the suburban monitoring site were weaker. Potential O-3 transboundary sources for Athens were mainly localized over Balkan Peninsula, Greece and the Aegean Sea, Potential Source Contribution Function hotspots were isolated over the industrialized area of Ptolemaida basin and above the region of Thessaloniki. Potential regional O-3 sources for Ioannina were indicated across northern Greece and Balkan Peninsula, whereas peak Potential Source Contribution Function values were particularly observed over the urban area of Sofia in Bulgaria. The implemented methods, revealed local and potential transboundary source areas of O-3, influencing Athens and Ioannina. Differences among the two cities were highlighted and the role of topography was emerged. These findings can be used in order to reduce the emission of O-3 precursors. (C) 2014 Elsevier B.V. All rights reserved.