Analysis of the columnar radiative properties retrieved during African desert dust events over Granada (2005–2010) using principal plane sky radiances and spheroids retrieval procedure

The southern Iberian Peninsula is an important area for studying the columnar radiative properties of African desert dust air masses reaching Europe. The Aerosol Optical Depth (AOD) and Angström coefficient, α (440–1020 nm), have been retrieved during the dust events reached at surface from 2005 to 2010 at Granada (37.18°N, 3.58°W, 680 m a.m.s.l), using extinction measurements by means of a CIMEL CE 318-1 sun-photometer. In addition, sky radiance measurements performed in principal plane in conjunction with solar irradiance measurements were used to retrieve columnar aerosol size distributions, single scattering albedo and asymmetry parameter. During these desert dust intrusions, high values of AOD at 440 nm (0.27 ± 0.17) and low values of α (0.4 ± 0.2) were found. These values indicate both high aerosol load and predominance of coarse particles during these events. The aerosol volume size distributions were bimodal, with the fine and coarse radius mode centered at 0.20 μm and 2.41 μm, respectively. The mean coarse to fine volume concentration ratio value was 11 ± 6, showing a predominance of coarse particles in good agreement with α analysis. During these events, columnar aerosol single scattering albedo (ω0) increased with wavelength in accordance with previous works. However, the obtained values of ω0 in all wavelengths were lower than those reported by other authors during desert dust intrusions. The mixing of desert dust with absorbing particles from anthropogenic origin could explain the low ω0 values measured in the study area.