Aerosol properties over two urban sites in South Spain during an extended stagnation episode in winter season

► Study of an intensive and long-lasting aerosol event at regional level. ► Characterization of the atmospheric thermodynamic structure during this event. ► Drastic increase in the aerosol fine concentration during the stagnation episode. ► Increase in modal radius and width of fine particles mode due to growth processes. ► Unusual high single scattering albedo with neutral spectral dependence.