2014 Volume 92A Pages 1-16
Aerosol optical properties at the Alpine station of Saint-Christophe, northern Italy are measured with a POM-02 sky radiometer. Diffuse radiances from the sky and direct sun irradiances are processed with SKYRAD and SUNRAD algorithms, respectively, providing consistent results. The aerosol optical depth at the station is generally very low (0.10 at a wavelength of 500 nm); however, spikes (up to 0.75) can occur due to the transport of Saharan dust and smoke clouds moving on an intercontinental scale, according to NAAPS and HYSPLIT models. In addition, the aerosol microphysical properties are analyzed by means of the Ångström exponent and its spectral variation, which allows discrimination between different types of particles and the assessment of possible contamination by clouds. Influence by local meteorology and anthropogenic emissions is investigated, providing useful information to understand the pollution dynamics in mountainous regions. Finally, we highlight some algorithmic and instrumental issues that are still poorly understood.