Influence of Saharan Dust Transport Events on PM2.5 Concentrations and Composition over Athens

The evaluation of the contribution of natural sources to PM10 and PM2.5 concentrations is a priority especially for the countries of European south strongly influenced by Saharan dust transport events. Daily PM2.5 concentrations and composition were monitored at an urban site at 14 m above ground level, at the National Technical University of Athens campus from February to December 2010. The typical dust constituents Si, Al, Fe, K, Ca, Mg, and Ti were determined by wavelength dispersive X-ray fluorescence spectrometry (WDXRF). Sulfur, a tracer of anthropogenic origin and major constituent of PM2.5, was determined by both WDXRF and ionic chromatography. The contribution of dust and sulfates in PM2.5 was calculated from the analytical determinations. An annual mean of 20 mu g/m(3) was calculated from the mean daily PM2.5 concentrations data. Twenty-two per cent of daily concentrations of PM2.5 reached or exceeded the EU annual target concentration of 25 mu g/m(3). The exceedances occurred during 13 short periods of 1-4 days. Back-trajectory analysis was performed for these periods in order to identify the air masses origin. From these periods, ten periods were associated to Saharan dust transport events. The most intense dust transport event occurred between February 17th and 20th and was responsible for the highest recorded PM2.5 concentration of 100 mu g/m(3) where the dust contribution in PM2.5 reached 96 %. The other dust transport events were less intense and corresponded to less pronounced enhancements of PM2.5 concentrations, and their contribution ranged from 15 to 39 % in PM2.5 concentrations. Air masses originated from northwest Africa while the influence of central Sahara was quite smaller.