Estimation of atmospheric turbidity over Ghardaı̈a city

The atmospheric turbidity expresses the attenuation of the solar radiation that reaches the Earth’s surface under cloudless sky and describes the optical thickness of the atmosphere. We investigate the atmospheric turbidity over Ghardaı̈a city using two turbidity parameters, the Linke turbidity factor and the Angström turbidity coefficient. Their values and temporal variation are obtained from data recorded between 2004 and 2008 at Ghardaı̈a. The results show that both parameters have the same trend along the year. They reach their maximum around summer months and their minimum around winter months. The monthly average value varies between 1.3 and 5.6 for the Linke turbidity factor and between 0.02 and 0.19 for the Angström turbidity coefficient. We find that 39.8 % of the Linke turbidity factor values are less than 3, 47.5 % are between 3 and 5 and only 12.7 % are greater than 5. For the Angström turbidity coefficient, 9.4 % of the values are less than 0.02, 75.4 % are between 0.02 and 0.15 and 15.2 % exceed 0.15