Optical properties of aerosols over the eastern Mediterranean

Measurements of aerosol optical properties, size distribution and chemical composition were conducted at Finokalia, a remote coastal site on the Greek island of Crete (35°19′N, 25°40′E) during July 2000 and January 2001. During the summer campaign the total scattering coefficient, σSP, (at a wavelength of 550 nm) ranged from 13 to 120 Mm−1 (mean=44.2 Mm−1, standard deviation=17.5) whilst during the winter it ranged from 7.22 to 37.8 Mm−1 (mean=18.42 Mm−1, standard deviation=6.61). A distinct diurnal variation in scattering coefficients was observed, with minima occurring during the early morning and maxima in the late afternoon during the summer and late evening during the winter. The mean value of the Ångström exponent was 1.47 during the summer and 1.28 during the winter, suggesting a larger fraction of smaller particles at the site during the summer. This was confirmed by continuous measurements of the aerosol size distribution. An analysis of the single scattering albedo suggests that there is a more absorbing fraction in the particle composition in the summer than during the winter. An investigation of air mass origins on aerosol optical properties indicated that those from Turkey and Central/Eastern Europe were highly polluted with a corresponding impact on aerosol optical properties. A linear relationship was obtained between the total scattering coefficient and both the non-sea-salt sulphate concentrations and the fine aerosol fraction.