The most important aerosol properties for determining aerosol effect in the solar radiation reaching the earth's surface
are the aerosol extinction optical depth and the single scattering albedo (SSA). Most of the latest studies, dealing with
aerosol direct or indirect effects, are based on the analysis of aerosol optical depth in a regional or global scale, while
SSA is typically assumed based on theoretical assumptions and not direct measurements. Especially for the retrieval of
SSA in the UV wavelengths only limited work has been available in the literature.
In the frame of SCOUT-O3 project, the variability of the aerosol SSA in the UV and visible range was investigated
during an experimental campaign. The campaign took place in July 2006 at Thessaloniki, Greece, an urban environment
with high temporal aerosol variability. SSA values were calculated using measured aerosol optical depth, direct and
diffuse irradiance as input to radiative transfer models. The measurements were performed by co-located UV-MFRSR
and AERONET CIMEL filter radiometers, as well as by two spectroradiometers. In addition, vertical aerosol profile
measurements with LIDAR and in-situ information about the aerosol optical properties at ground level with a
nephelometer and an aethalometer were available.
The ground-based measurements revealed a strong diurnal cycle in the SSA measured in-situ at ground level (from 0.75
to 0.87 at 450nm), which could be related to the variability of the wind speed, the boundary layer height and the local
aerosol emissions. The reasons for SSA differences obtained by different techniques are analyzed for the first time to
provide recommendations for more accurate column SSA measurements.