Aerosol seasonal variability over the Mediterranean region and relative impact of maritime, continental and Saharan dust particles over the basin from MODIS data in the year 2001

Abstract

Abstract.The one-year (2001) record of aerosol data from the space borne Moderate Resolution Imaging Spectroradiometer (MODIS) is analyzed focusing on the Mediterranean region. The MODIS aerosol optical thickness standard product (AOT at 550 nm) provided over both land and ocean is employed to evaluate the seasonal and spatial variability of the atmospheric particulate over the region. Expected accuracy of the MODIS AOT is (±0.05±0.2×AOT) over land and (±0.03±0.05×AOT) over ocean. The seasonal analysis reveals a significant AOT variability all over the region, with minimum values in Winter (AOT<0.15) and maximum in Summer (AOT>0.2). The spatial variability is also found to be considerable, particularly over land. The impact of some major urban sites and industrialized areas is detectable. For the sole Mediterranean basin, a method (aerosol mask) was implemented to separate the contribution of maritime, continental and desert dust aerosol to the total AOT. Input of both continental and desert dust particles is well captured, showing North-to-South and South-to-North AOT gradients, respectively. A quantitative summary of the AOT seasonal and regional variability is given for different sectors of the Mediterranean basin. Results of this summary were also used to test the aerosol mask assumptions and indicate the method adopted to be suitable for the aerosol type selection. Estimates of the atmospheric aerosol mass load were performed employing specifically-derived massto-extinction efficiencies (α). For each aerosol type, a reliable mean α value was determined on the basis of both lidar measurements of extinction and aerosol models. These estimates indicate a total of 43 Mtons of desert dust suspended over the basin during 2001. A comparable value is derived for maritime aerosol. Opposite to the dust case, a minor seasonal variability (within 15%) of maritime aerosol mass is Correspondence to: F. Barnaba (f.barnaba@isac.cnr.it) found. This latter result is considered a further check of the suitability of the methodology adopted to separate, on the basis of MODIS data, the three aerosol types which dominate the Mediterranean region.

Profiling of fine and coarse particle mass: case studies of Saharan dust and Eyjafjallajökull/Grimsvötn volcanic plumes

“…In Table 2, we assume that these values still hold for 500-550 nm (i.e., we assume no wavelength-dependence of the extinction coefficient and AOT for coarse particles). The model results of Barnaba and Gobbi (2004) show a likewise large range of potential dust values. The detailed study of the relationships between particle backscatter, extinction, surface area, and volume concentrations for various aerosol types can be found in Gobbi (2001, 2002).…”

“…1, Helgoland and Hamburg versus Leipzig values). The model simulations by Barnaba and Gobbi (2004) in Table 2 with k ext,f values close to 3.5 m 2 g −1 considering the full range of realistic size distributions of aged fine-mode European haze do not show this variability. In accordance with the model results, the values of v f /τ f observed over Leipzig (in urban air, less affected by soil dust, and taken far away from marine environments) also show relatively constant values around 3.5 m 2 g −1 .…”

“…[ 10 Barnaba and Gobbi (2004) 3.50 ± 0.1 0.18 ± 0.005 Modeling study, full range of realistic size distributions Ansmann et al (2011b) 3.50 ± 0.4 0.18 ± 0.02 AERONET, remote sensing, Germany Sicard et al (2012) 2.40 ± 0.1 0.25 ± 0.01 AERONET, remote sensing, Spain of uncertainties remain. Airborne in-situ observations may suffer from high uncertainties in the retrieval of the entire particle size spectrum and the subsequent retrieval of the coarse-mode particle volume concentration.…”

“…In addition the ratio of frequently measured volume concentration to volume extinction coefficient V /σ ext = 1/(k ext ρ) is given. A few modeled values (Hess et al, 1998;Barnaba and Gobbi, 2004) for coarse-mode as well as for fine-mode particles are added. Values are taken from the indicated literature (reference).…”

Relating aerosol absorption due to soot, organic carbon, and dust to emission sources determined from in-situ chemical measurements

“…Russell et al (2010) highlighted that many recent studies have shown the persistent connections between aerosol absorbing species and the wavelength dependence of absorption. Thus, numerous studies have classified absorbing aerosol types from optical properties measured on ground stations (Eck et al, 1999;Dubovik et al, 2002;Collaud Coen et al, 2004;Fialho et al, 2005;Meloni et al, 2006;Kalapureddy et al, 2009;Mielonen et al, 2009;Giles et al, 2011Giles et al, , 2012 and from satellites (Higurashi and Nakajima, 2002;Barnaba and Gobbi, 2004;Jeong and Li, 2005;Kaufman et al, 2005;Torres et al, 2005;Kaskaoutis et al, 2007;Kim et al, 2007;Yu et al, 2009). In this study, in-situ optical properties and single particle chemical composition measured during three aircraft field campaigns are combined in order to validate a methodology for the estimation of absorbing aerosol types using spectral optical properties.…”