Three-year ground based measurements of Aerosol Optical Depth over the Eastern Mediterranean: the urban environment of Athens
- ISSN: 1680-7367, 1680-7367
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 Aangstroem 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. Secondary contributors of high aerosol loadings over Athens are identified, 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. 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 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.