Column-integrated aerosol optical properties in the free troposphere: case study-Sierra Nevada, Spain

From spectral solar irradiance extinction measurements in the visible range carried out at Sierra Nevada (2950 m a.s.l.) during July 1998, the characteristics of the aerosol column in the free troposphere have been measured. The results show that in stable atmospheric conditions, the column-integrated aerosol takes an optical depth (AOD) at 500 nm of 0.02 ± 0.02, and an average radius in the accumulation mode of 0.15 μm, with a likely Atlantic origin. In unstable situations, the AOD at 500 nm can increase by more than an order of magnitude, and the aerosols´ origin is uncertain, since air masses can arrive from different sources at different altitudes.