Direct solar radiation measured with a pyrheliometer installed at the meteorological station of Sidi Bou Said (Northern Tunisia) is used to investigate the atmospheric turbidity using Linke's factor. The obtained results indicate high variability of the diurnal and seasonal components of atmospheric turbidity, with a summer maximum and a winter minimum. The correlation between atmospheric turbidity and wind speed and direction shows an increase of atmospheric turbidity particularly due to the transport of particles of continental origin in the west sector. In the east sector, the correlation between atmospheric turbidity and specific humidity shows that the summer maximum is due to the heavy water vapor content of maritime air masses, carried by the north-eastern winds prevalent during this season combined with local continental particles. Correlation of atmospheric turbidity with diffuse radiation for maritime and continental air masses is derived. (C) 2008 Elsevier Ltd. All rights reserved.