Cases of aerosol optical depth estimation in the Athens area, Greece

This work estimates the Ångström turbidity coefficients and investigates the variation of the aerosol optical depth (AOD) in the Athens area, during different atmospheric conditions. The AOD is estimated in the wavelength band of 400-670 nm from direct-beam spectral irradiance measurements using ground-based instrumentation, during an experimental campaign performed in the period 22 September-1 October 2002. All data were collected under clear-sky conditions near the city center of Athens; the AODs were estimated relative to the local zenith to avoid the influence of the optical air mass. The study shows that the AOD is influenced by wind regime and traffic in the Athens area. The Angstrom's turbidity coefficients and the AOD values were found to be higher under the influence of South-sector winds compared to those from the North-sector. Under South-sector low winds, the pollutants are accumulated in the Athens basin. On the contrary, the North-sector winds clean the atmosphere.