Seasonal variation of aerosols properties in South Italy: a study on aerosol optical depths, Angstrom turbidity parameters and aerosol size distributions

Direct solar radiation measurements, carried out from June 2001 to October 2001 in a site in South Italy, have been analysed. This site is characteristic of a continental area but it can be affected by the intrusion of marine and dust particles. Solar irradiance was measured using a high-resolution spectroradiometer, working in the visible range (400800 nm), collecting about 500 spectra under cloudless conditions. From the aerosol optical depths we estimated the Angstrom turbidity parameters, by means of a least-square fitting procedure. Finally, a Twomey modified inversion technique allowed us to estimate the aerosol size distribution, obtaining mostly two-modal functions. Integrating the second mode of the aerosol size distribution, it was surprising to find a high correlation with the beta parameter only for data corresponding to low turbidity conditions.