Analysis of the aerosol radiative forcing over a Mediterranean urban coastal site

The aerosol radiative forcing for the period 2003–2011 has been analyzed in Burjassot, Spain, an urban coastal site on the western Mediterranean, using measurements of global solar irradiance and aerosol properties, as well as simulated data. The aerosol radiative forcing was calculated at 5 minute intervals, and then integrated over 24 h to obtain daily mean values for 200 complete days under cloud-free skies. The monthly mean values of the aerosol radiative forcing showed a clear variation during the year, associated to the annual variability of the aerosol optical depth at 500 nm, ranging from − 6 to − 29 Wm− 2 at the surface, and from − 1.5 to − 3.9 Wm− 2 at the top of the atmosphere, with mean values for the whole period of − 17 ± 10 Wm− 2 and − 2.2 ± 1.3 Wm− 2, respectively. The aerosol radiative forcing efficiency was found to be − 139 ± 3 Wm− 2 at the surface and − 19.2 ± 0.3 Wm− 2 at the top of the atmosphere. These negative values, which correspond to cooling effects, suggest a significant absorption of solar radiation by the atmosphere, showing the important role of atmospheric aerosols in this urban site of the Mediterranean.