The June 2007 Saharan dust event in the central Mediterranean: Observations and radiative effects in marine, urban, and sub-urban environments J.L. Gómez-Amo a, b, * , V. Pinti a, c , T. Di Iorio d , A. di Sarra a , D. Meloni a , S. Becagli e , V. Bellantone f , M. Cacciani d , D. Fuà d , M.R. Perrone f a ENEA, Laboratory for Earth Observations and Analyses, S. Maria di Galeria, Italy b Departament de Física de la Terra i Termodinàmica, Universitat de València, Spain c Institute for Atmosphere and Climate Science, ETHZ, Zurich, Switzerland d Dipartimento di Fisica, Università “Sapienza”, Rome, Italy e Dipartimento di Chimica, Università di Firenze, Italy f Dipartimento di Fisica, Università del Salento, Lecce, Italy article info Article history: Received 18 February 2011 Received in revised form 4 May 2011 Accepted 15 June 2011 Keywords: Aerosol optical properties Vertical distribution Radiative forcing Desert dust event abstract A desert dust episode in June 2007 and its radiative effects on the energy budget have been studied at three Italian stations (Rome, Lecce and Lampedusa) with the aim of investigating the interactions with different conditions and aerosol types over the Mediterranean. The three sites are representative for urban (Rome), sub-urban/rural (Lecce), and marine (Lampedusa) environment, respectively in the central Mediterranean region. Measured ground-based column-averaged aerosol optical properties and aerosol extinction profiles were used to initialize the MODTRAN4 radiative transfer model. The radiative transfer model was used to estimate the shortwave aerosol radiative forcing (ARF) and its forcing efficiency (FE) at two different solar zenith angles (20  and 60  ) in the 280e2800 nm spectral range. The goal was to investigate the role of different aerosol types in the atmospheric boundary layer on the radiative budget during a dust event. During the event the aerosol optical depth was moderately high and similar at the three stations, with a maximum value of about 0.6. The Ångström exponent was found to increase with the distance from the source (0.21, 0.36, and 0.43 at Lampedusa, Rome, and Lecce, respectively). Differences in the aerosol optical properties were observed, also depending on the aerosol type assumed in the boundary layer. The estimated direct aerosol forcing appears to depend on the changes in aerosol properties and to the surface albedo. The results show that the desert dust produces a cooling effect at both surface (largest ARF of 224 W m 2 at 20  solar zenith angle at Rome) and top of the atmosphere (largest ARF of 19 W m 2 at 20  solar zenith angle at Lecce). The cooling is largest in the rural and smallest in the marine environment. The surface forcing efficiency appears to be strongly affected by the aerosol absorption in the BL. Large differences exist between our results and the FE determinations by AERONET, derived considering a single layer with homogeneous optical properties and prescribed vertical distribution. The FE deviations are around 20, 60, and 40% at the surface, TOA, and in the atmosphere, respectively. These results suggest that the detailed description of the vertical distribution of the aerosol properties is needed for an accurate determination of its radiative effects. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Every year a large amount of desert dust is introduced in the atmosphere. The strong convection over desert regions can trans- port sand up to the middle and high troposphere (e.g., Di Iorio et al., 2009), from which it may be transported to great distances. The Sahara desert is the most important source of desert dust aerosols: every year about one hundred million tons of dust particles are believed to be transported from these regions (Prospero, 1996) to the tropical North Atlantic Ocean and the Mediterranean (Rodriguez et al., 2001; Prospero, 1999). The Mediterranean area has been repeatedly suggested as one of the areas where aerosols are expected to play a significant climatic role (e.g., Kallos et al., 2007; di Sarra et al., 2008). Desert dust transport over the Mediterranean Sea is mainly due to motions at * Corresponding author. ENEA, Laboratory for Earth Observations and Analyses, via Anguillarese 301, 00123, S. Maria di Galeria (Rome), Italy. E-mail address: joseluis.gomezamo@enea.it (J.L. Gómez-Amo). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.06.045 Atmospheric Environment 45 (2011) 5385e5393