Three-year ground based measurements of aerosol optical depth over the Eastern Mediterranean: the urban environment of Athens - Gerasopoulos, E.; V. Amiridis; S. Kazadzis; Kokkalis, P.; Eleftheratos, K.; Andreae, M. O.; Andreae, T. W.; El-Askary, H.; Zerefos, C. S. (Atmos. Chem. Phys., 2011)