Variability of aerosol optical properties in the Western Mediterranean Basin

Abstract

Abstract. Aerosol light scattering, absorption and particulate matter (PM) concentrations were measured at Montseny, a regional background site in the Western Mediterranean Basin (WMB) which is part of the European Supersite for Atmospheric Aerosol Research (EUSAAR). Off line analyses of 24 h PM filters collected with Hi-Vol instruments were performed for the determination of the main chemical components of PM. Mean scattering and hemispheric backscattering coefficients (@ 635 nm) were 26.6±23.2 Mm −1 and 4.3±2.7 Mm −1 , respectively and the mean aerosol absorption coefficient (@ 637 nm) was 2.8±2.2 Mm −1 . Mean values of Single Scattering Albedo (SSA) andÅngström exponent (å) (calculated from 450 nm to 635 nm) at MSY were 0.90±0.05 and 1.3±0.5 respectively. A clear relationship was observed between the PM 1 /PM 10 and PM 2.5 /PM 10 ratios as a function of the calculatedÅngström exponents. Mass scattering cross sections (MSC) for fine mass and sulfate at 635 nm were 2.8±0.5 m 2 g −1 and 11.8±2.2 m 2 g −1 , respectively, while the mean aerosol absorption cross section (MAC) was 10.4±2.0 m 2 g −1 . The variability in aerosol optical properties in the WMB were largely explained by the origin and ageing of air masses over the measurement site. The MAC values appear dependent of particles aging: similar to the expected absorption cross-section for fresh emissions under Atlantic Advection episodes and higher under aerosol pollution episodes. The analysis of theÅngström exponent as a function of the origin the air masses revealed that polluted winter anticyclonic conditions and summer recirculation scenarios typical of the WMB led to an increase of fine particles in the atmosphere (å = 1.5±0.1) while the aerosol optical properties under Atlantic Advection episodes and Saharan dust outbreaks were clearly dominated by coarser particles (å = 1.0±0.4). The sea breeze played an important role Correspondence to: M. Pandolfi (marco.pandolfi@idaea.csic.es) in transporting pollutants from the developed WMB coastlines towards inland rural areas, changing the optical properties of aerosols. Aerosol scattering and backscattering coefficients increased by around 40 % in the afternoon when the sea breeze was fully developed while the absorption coefficient increased by more than 100 % as a consequence of the increase in the equivalent black carbon concentration (EBC) observed at MSY under sea breeze circulation.

Continental pollution in the Western Mediterranean basin: large variability of the aerosol single scattering albedo and influence on the direct shortwave radiative effect

“…Values of the single scattering albedo measured in this study are comparable with values reported at several other sites in the Central and Western Mediterranean region for pollution aerosols (Mallet et al, 2003(Mallet et al, , 2013Meloni et al, 2006;Saha et al, 2008;Di Biagio et al, 2009;Pandolfi et al, 2011). The single scattering albedo from these studies varies in the range 0.84-0.95 at 440 nm, 0.76-0.98 at 500-550 nm, and 0.80-0.87 at 870 nm.…”

“…In spite of this, the characterization of the optical properties of anthropogenic aerosols in this part of the basin remains only limited to coastal and inland regions (Mallet et al, 2003(Mallet et al, , 2011(Mallet et al, , 2013Lyamani et al, 2006;Estelles et al, 2007;Saha et al, 2008;Esteve et al, 2012;Piazzola et al, 2012;Pandolfi et al, 2011Pandolfi et al, , 2014, or remote islands actually far from the strong influence of continental outflows (Lyamani et al, 2015). Moreover, the majority of these studies uses remote-sensing measurements and analyse aerosol properties integrated over the entire atmospheric column, without information on their vertical variability.…”

Physical–chemical characterisation of the particulate matter inside two road tunnels in the São Paulo Metropolitan Area

“…The MAAP instrument uses a constant value of 6.6 m 2 g −1 , which is recommended by the manufacturer. However, this value has been the subject of strong debate (Pan et al, 2011;Pandolfi et al, 2011;Healy et al, 2012;Crippa et al, 2013). Here, the aerosol light absorption measured using the MAAP in the JQ tunnel was compared with EC determined from the collected filters by means of a Sunset analyser.…”

Impact of aerosol microphysical properties on mass scattering cross sections

“…[8] collected measurements of dry (RH < 40%) aerosol P M10 mass concentrations (gravimetric masses from 24h filters) and optical properties (scattering coefficients with Nephelometer AURORA 3000, Ecotech), in the period 2010-2014, at the Montseny regional background station (middle altitude emplacement within the Montseny Natural Park, Spain: 41…”