Aerosol radiative effects during two desert dust events in August 2012 over the Southwestern Iberian Peninsula

The ARF per unit of aerosol optical depth (AOD), called the aerosol radiative forcing efficiency (ARFE), is also evaluated for this shortwave spectral range. The ARFE values obtained for Évora and Badajoz during the first event are − 112.93 ± 6.60 W m− 2 and − 101.63 ± 10.73 W m− 2 per unit of AOD (500 nm), respectively, and, for the second event, − 92.44 ± 9.82 W m− 2 and − 87.85 ± 10.19 W m− 2 per unit of AOD (500 nm), respectively. These values also confirm the previous results, i.e., the first event causes a greater radiate cooling than the second one in both stations, although the second desert dust event is more intense, i.e., with higher aerosol optical depth and PM10 aerosol mass concentration. The presence of absorbing aerosols, together with dust, near the surface during the first event may explain the greater efficiency of this aerosol mixture to reduce the downward shortwave irradiance reaching the surface, inducing a greater radiative cooling than the second event.