Comparison of model calculations with spectral UV measurements during the SUSPEN campaign: The effect of aerosols

Spectral measurements of global solar irradiance, obtained under cloud-free conditions during the SUSPEN campaign (July 1997) in Thessaloniki, Greece, are compared with radiative transfer model calculations, showing an agreem ent to within +/-5% for wavelengths higher that 305 nm. The uncertainties i n the modeled spectra were analyzed with respect to the aerosol-related mod el input parameters (single-scattering albedo and asymmetry factor), which were not derivable from measurements. A range of single-scattering albedo v alues was used to investigate its impact on surface UV irradiance through c omparison of measurements with model calculations. It was found that a diff erence in the single-scattering albedo of 0.1 changes the model-measurement ratio by 7%-14%, depending on solar zenith angle. Finally, an attempt was made to relate the estimated values of single-scattering albedo to wind dir ection and relative humidity, which control the origin and type of the aero sols in the area.