Atmospheric aerosols and their impact on surface solar irradiation in Kerkennah Islands (eastern Tunisia)

• Positive correlation has been recorded between the surface aerosol concentrations on the one hand, and Linke turbidity factor (TL), Angström exponent (β), and diffuse fraction (DF) on the other hand
• Estimation of the contributions of the mineral dust (MD), sea salt (SS), and non sea salt sulfate (nSS) species on both TL and DF.

In order to assess the impact of the atmospheric particle load on the characteristics of the surface solar irradiation in Central Tunisia, four measurement campaigns have been carried out in periods selected in each season of 2010/2011 on the Kerkennah Islands. During each of these periods, the direct normal and global horizontal components of solar irradiation were measured, which allows determination of the atmospheric turbidity (Linke turbidity factor, TL, and Angström exponent, β) and of the diffuse fraction (DF) of the irradiation. In parallel, surface aerosols were sampled on filters and subsequently submitted to X-ray fluorescence (XRF) analysis for determination of their elemental composition and apportionment between the mineral dust (MD), sea salt (SS), and non sea salt sulfate (nSS) species. A significant positive correlation is found between the total aerosol concentration and both TL and DF, which indicates that over the measurement period surface aerosol is representative of the columnar particulate content of the atmosphere. A least square iterative routine used to separate the effects of each aerosol type shows that if on average MD, SS, and nSS explain 4, 19 and 12%, respectively, of the TL values, the increase of the MD concentrations during short-duration dust event is responsible for the largest observed values (TL = 6 on 15 April 2010). Similarly, if on average only about 9% of the global horizontal surface irradiation can be ascribed to aerosols, during the aforementioned dust event this share reaches 28%, 19% of which are due to mineral dust.