[1] During a 1-month campaign conducted in May 1999 in the frame of Photochemical Activity and Solar Ultraviolet Radiation (PAUR II) project, determination of the ionic composition and physical and optical properties of the aerosol have been performed at a coastal site in Crete. Non-sea-salt sulfate (nss-SO 4 2Ϫ ), nitrate (NO 3 Ϫ ) non-sea-salt calcium (nss-Ca 2ϩ ), and ammonium (NH 4 ϩ ) have been identified as the main non-sea-salt ionic components of the aerosol. Air mass origin was found to be an important factor controlling the variation of the above ions as well as their particle size distribution. During the experiment, aerosol scattering coefficient ranges from 2 to 51 (M m Ϫ1 ) with no significant difference between dusty and nondusty periods. Significant correlations have been observed between (NH 4 ) 2 SO 4 mass measured during the campaign, aerosol scattering coefficient, and aerosol single-scattering albedo indicating the key role of (NH 4 ) 2 SO 4 in determining the radiative forcing of the eastern Mediterranean area. Finally, non-sea-salt calcium was found to better reproduce the variation of optical depth, more than any other ionic species.