1Institute for Environmental Research and Sustainable Development, National Observatory of Athens, I. Metaxa and Vas. Pavlou, 15236, P. Penteli, Athens, Greece
2Insitute for Space Applications and Remote Sensing, National Observatory of Athens, P. Penteli, Athens, Greece
3National Technical University of Athens, Laboratory of Lasers and Applications, Athens, Greece
4National Kapodistrian University of Athens, Geology Department, Athens, Greece
5Biomedical Research Foundation, Academy of Athens, Athens, Greece
6Biogeochemistry Department, Max Planck Institute for Chemistry, 55020 Mainz, Germany
7School of Earth and Environmental Sciences, Schmid College of Science, Chapman University, Orange, CA, USA
8Department of Environmental Sciences, Faculty of Science, Alexandria University, Egypt
Received: 18 Aug 2010 – Discussion started: 18 Nov 2010
Abstract. Three years (2006–2008) of ground-based observations of the Aerosol Optical Depth (AOD) in the urban environment of Athens, in the Eastern Mediterranean, are analysed in this work. Measurements were acquired with a Multi-Filter Rotating Shadowband Radiometer at five wavelengths. The daily average AOD at 500 nm is 0.23, and the mean Ångström coefficient calculated between 415 and 867 nm is 1.41. The annual variability of AOD has a spring maximum dominated by coarse dust particles from the Sahara (AOD 0.34–0.42), while the diurnal pattern is typical for urban sites, with AOD steadily increasing throughout the day. The greatest contribution to the annually averaged AOD, accounting for almost 40%, comes from regional and local sources (namely the Istanbul metropolitan area, the extended areas of biomass burning around the north coast of the Black Sea, power plants spread throughout the Balkans and the industrial area in the Po valley, with average daily AOD in the range of 0.25–0.35). An additional important contribution (23%) is dust from Africa, whereas the rest of Europe contributes another 22%. The geographical distribution of the above sources in conjunction with the prevailing synoptic situation and contribution of local sources, lead to mixed types of aerosols over Athens, with highly variable contribution of fine and coarse particles to AOD in the range 10%–90%. This is the first long-term, ground based data set available for Athens, and it has also been used for the validation of satellite derived AOD by MODIS, showing good agreement on an annual basis, but with an overestimation of satellite AODs in the warm period.
Revised: 14 Feb 2011 – Accepted: 21 Feb 2011 – Published: 10 Mar 2011
Gerasopoulos, E., Amiridis, V., Kazadzis, S., Kokkalis, P., Eleftheratos, K., Andreae, M. O., Andreae, T. W., El-Askary, H., and Zerefos, C. S.: Three-year ground based measurements of aerosol optical depth over the Eastern Mediterranean: the urban environment of Athens, Atmos. Chem. Phys., 11, 2145-2159, doi:10.5194/acp-11-2145-2011, 2011.