Impact of desert dust events on short- and long-wave radiation at the surface over south-eastern Italy

Clear-sky short-wave (SW) and long-wave (LW) irradiance measurements at the surface were combined with AErosol RObotic NETwork (AERONET) sun/sky photometer aerosol products to study the desert dust impact on irradiance measurements at a Central Mediterranean site during the year 2012, by comparing measurements performed on dusty and dust-free days. Daily mean values of both the aerosol Angsotrom exponent (angstrom), calculated from the aerosol optical depths (AOD) at 440 and 870 nm retrieved from AERONET sun/sky photometer measurements, and the desert dust loading (DL) from the Barcelona Supercomputing Center Dust REgional Atmospheric Model (BSC-DREAM8b) were used to select dusty days. In particular, we have identified as dusty days the ones characterized by angstrom values less than 0.9 and DL values larger than 0.5 g m(-2). The desert dust events occurred from March to September during the analyzed year, in which we have identified 30 and 96 clear-sky dusty and dust-free days, respectively. The daytime SWand LWdownward fluxes (F-DN) on average decreased by 8 % and increased by 3 %, respectively, on the dusty days with respect to the dust-free ones. These flux variations were associated with an average increase of 40 % of the AOD at 440 nm and an average decrease of 39 % of the fine mode fraction (eta) at 500 nm. The daily means of SW-and LW-F-DN were reasonably correlated with the corresponding AOD and eta values on the dusty days, revealing that the increase of the coarse mode particle contribution was mainly responsible for the flux changes. Conversely, both the SW- and the LW-F-DN values were not correlated with the corresponding AOD and eta values on the dust-free days.