Tropospheric aerosols in the Mediterranean: 1. Microphysical and optical properties

Abstract

[1] Measurements of the aerosol properties were carried out at the island of Lampedusa, in the Mediterranean, in May 1999, as part of the Photochemical Activity and Ultraviolet Radiation modulating factors II campaign. Data from ground-based lidar and Sun photometer, and particle counters aboard an instrumented ultralight aircraft, are used in this study. Three different cases, when all the measurements were available in cloud-free conditions, were identified to derive the aerosol microphysical and optical properties. In one of these cases (18 May) the airmasses originated from Africa, and were loaded with a large amount of desert dust. In the other two cases (25 May and 27 May) the airmasses passed over Europe before reaching Lampedusa from North. The microphysical and optical properties of the aerosol strongly depend on the origin of the airmasses. The amount of particles in the 1-6 mm range of radii and the average aerosol surface area per unit volume are larger in the desert dust case than on 25 May and 27 May. The real part of the refractive index of the desert dust at 532 nm is between 1.52 and 1.58; its imaginary part is 5-7 Â 10 À3 and the single scattering albedo is about 0.7-0.75. The aerosol layer of 18 May closest to the surface, that probably contains a mixture of desert dust and marine aerosol, displays a smaller imaginary part (1.2 Â 10 À3 ) and a larger single scattering albedo (0.91). The aerosols originating from the North Atlantic and Europe have a real part of the refractive index between 1.35 and 1.49, and an imaginary part ranging from 8 Â 10 À4 to 1.8 Â 10 À2 ; the single scattering albedo at 532 nm (0.78-0.95) is larger than for desert dust values. The smallest value of the single scattering albedo (0.69) corresponds to an airmass originating from North, characterized by a large imaginary part of the refractive index. The asymmetry factor of the desert dust appears consistently larger for the desert dust (0.75-0.8) than for the other cases (0.61-0.72). The extinction-to-backscattering ratio, also derived from the measurements, is about 40 sr for the desert dust, and between 60 and 81 sr for the aerosol of northern origin. Simple estimates of the aerosol average direct shortwave radiative forcing at the top of the atmosphere indicate that all considered aerosol types induce a cooling. The radiative forcing per unit optical depth of the aerosol originating from North is about À37 Wm À2 over ocean and À(12-17) Wm À2 over land, while is À29 Wm À2 over ocean and À8 Wm À2 over land for desert dust. The largest forcing is however produced by the desert aerosols that generally display a considerably larger optical depth.

Continental pollution in the western Mediterranean basin: vertical profiles of aerosol and trace gases measured over the sea during TRAQA 2012 and SAFMED 2013

“…Junkermann, 2001;Meloni et al, 2003;Di Iorio et al, 2003;Pace et al, 2015) and eastern (e.g. Formenti et al, 2002;Dulac and Chazette, 2003) parts of the basin thus improving the description of the atmospheric composition and structure over the whole Mediterranean area.…”

Aerosol properties over the western Mediterranean basin: temporal and spatial variability

“…To date, a large number of studies has been done focusing on the eastern and central regions (e.g., Formenti et al, 1998;Gerasopoulos et al, 2003;Di Iorio et al, 2003;Kubilay et al, 2003;Pace et al, 2005Pace et al, , 2006Fotiadi et al, 2006;Meloni et al, 2007Meloni et al, , 2008Di Sarra et al, 2008;Di Biagio et al, 2010;Boselli et al, 2012). However, few studies have been done in the western Mediterranean Basin (Horvath et al, 2002;Alados-Arboledas et al, 2003;Mallet et al, 2003;Estellés et al, 2007;Saha et al, 2008;Pérez-Ramírez et al, 2012, Foyo-Moreno et al, 2014.…”

Temporal consistency of lidar observations during aerosol transport events in the framework of the ChArMEx/ADRIMED campaign at Minorca in June 2013

“…2002), (iii) with a lidar deployed in Crete (Gobbi et al, 2000) or an instrumented ultralight aircraft in Lampedusa (Di Iorio et al, 2003) during the Photochemical Activity and Ultraviolet Radiation (PAUR II) campaign in 1999, (iv) over the eastern Mediterranean basin during the Mediterranean Intensive Oxidant Study (MINOS; Lelieveld et al, 2002) and Mediterranean Israeli Dust Experiment (MEIDEX; Levin et al, 2005) in 2001, and over the urban and industrial region of Marseille-Fos-Berre on the French Mediterranean coast also in 2001 (Cros et al, 2004;Cachier et al, 2005);and (vi) in the framework of the EARLINET network (Papayannis et al, 2008). Such past experiments have produced very useful information about the vertical distribution of Mediterranean aerosol optical properties, based on in situ observations and lidar measurements.…”