Abstract
In this study, aerosol optical depth (AOD) measurements, from a MFR sun photometer operating in Athens, were compared with columnar dust loading estimations, from the BSC-DREAM model, during identified dust events, in order to extract the typical specific extinction cross-section for dust over the area. The selected urban environment of Athens provided us with the opportunity to investigate the mixing of dust and urban pollution and to estimate the contribution of the latter. The specific extinction cross-section for dust at 500 nm was found to be equal to sigma (sub 500) (super *) =0.64+ or -0.04 m (super 2) g, typical for medium to large distances from dust sources, with weak wavelength dependence in the visible and near infrared band (0.4-0.9 mu m). The model showed a tendency to underpredict AOD levels for increasing values of the Angstrom exponent, indicative of fine particles of anthropogenic origin inside the boundary layer. On average we found an AOD under-prediction of 10-15% for Angstrom exponents in the range of 0 to 1 and 30-40% in the range of 1 to 2. Additionally, modelled surface concentrations were evaluated against surface PM (sub 10) measurements. Model values were lower than measured surface concentrations by 30% which, in conjunction with large scatter, indicated that the effect of the boundary layer anthropogenic contribution to columnar dust loadings is amplified near the ground.