The role of aerosol models of the SMARTS code in predicting the spectral direct-beam irradiance in an urban area

Measurements of the ground-level spectral distribution of the direct-beam solar irradiance between 300 and 1000 nm were made in Athens, Greece, in May 1995. Results obtained using simple model for the atmospheric radiative transfer of sunshine (SMARTS) (version 2.9.2) parametric model for the urban atmosphere of Athens are analyzed and compared to the ground-level experimental spectral solar irradiance measurements obtained by the passive pyrheliometric scanner (PPS) in three discrete bands, UV (320–400 nm), VIS (400–700 nm) and NIR (700–1000 nm). The study uses two different input parameters for the aerosol characterization: the aerosol optical depth at 500 nm, tα0.5, and the Ångström turbidity coefficient, β. The results clearly show that the nine aerosol models implemented in the SMARTS code lead to quite different predictions of the direct-beam spectrum, strongly depended on the input parameter. In all cases the inadequacies between the measured and the modeled direct-beam spectra are lower and higher when the urban and maritime aerosol models are used, respectively.