Determination of Linke turbidity factor from solar radiation measurement in northern Tunisia

The attenuation of solar radiation through a real atmosphere versus that through a clean dry atmosphere gives an indication of the atmospheric turbidity. Study of atmospheric turbidity is important in meteorology, climatology and for monitoring of atmospheric pollution. The Linke turbidity factor refers to the whole spectrum, that is, overall spectrally integrated attenuation, which includes presence of gaseous water vapour and aerosols. In this work, a procedure for calculation of Linke turbidity factor is adopted using pyrheliometric measurements in a coastal tourist location in Tunisia (Sidi Bou Said), during three summer months (June, July and August 1999). Real diurnal and monthly variations of the TL turbidity factor are found in the three studied months, with a maximum in August afternoon and a minimum in July morning. The increase of TL is an indication for increasing atmospheric turbidity level (pollution). The correlation between atmospheric turbidity and the local weather conditions shows that this increase is essentially due to the heavy water vapour content of maritime air masses, carried by the north-eastern winds prevalent during the afternoon. A second pollution source is the dust content of the continental air masses carried by western and southern winds prevalent in the morning. Next to this can be added the influence of traffic at rush hours and during the afternoon of summer holidays. (Author)