Aerosol optical characteristics from a summer campaign in an urban coastalMediterranean area

We present a preliminary study of some optical properties of atmospheric ae rosols over the area of Valencia, Spain, a coastal Mediterranean city. Meas urements of spectral direct irradiance in the 300-1100 mn range were taken simultaneously at three sites: rural-continental, rural-coastal, and urban- costal, all located within a 50 km radius of the city of Valencia. The irra diance measurements were obtained using three Li-cor 1800 spectroradiometer s provided with radiance limiting tubes with field of views (FOVs) of 4.7 d egrees. The measurements were made under clear sky conditions during a fiel d campaign carried out in the summer of 1998. In order to avoid the uncerta inties associated with the determination of the water vapor content and the other atmospheric constituents, the analysis of the spectral aerosol optic al thickness (AOT) values was limited to the 400-670 nm spectral band. From the values of the spectral AOT, both the Angstrom coefficients and the aer osol size distributions were obtained. The results show the great dependenc e of the optical aerosol characteristic on the direction of the prevailing winds (maritime or continental) in this area.