Trace element variation in size-fractionated African desert dusts

Castillo, Sonia; Moreno, Teresa; Querol, Xavier; Alastuey, Andrés; Cuevas, E.; Herrmann, Ludger; Mounkaila, Mohammed; Gibbons, Wes

doi:10.1016/j.jaridenv.2007.12.007

Cited by 128 publications

(69 citation statements)

References 52 publications

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“…Figure 8 shows that both source areas display Ca / Al and Mg / Al ratios higher than the mean crustal composition. The high Ca / Al are related to the elevated carbonate contents in the Saharan sediments, found in north-western (Morocco and Atlas region; Criado and Dorta, 2003;Khiri et al, 2004;Linke et al, 2006;Moreno et al, 2006;Castillo et al, 2008) and north-eastern Africa (Egypt, Libya; Linke et al, 2006, Israel, Ganor and Foner, 1996, Jordan, Abed et al, 2009. Intermediate values were reported for southern Egypt and northern Sudan (Tomadin et al, 1989;Sharif, 1995), while lower Ca contents (Ca / Al<0.5) were found in samples from central and southern Algeria and the Sahel zone.…”

Section: Source Areas Of Saharan Dust Aerosolmentioning

confidence: 99%

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

et al. 2014

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Abstract. This study aims to determine the mineral contribution to PM 10 in the central Mediterranean Sea, based on 7 yr of daily PM 10 samplings made on the island of Lampedusa (35.5 • N, 12.6 • E).The chemical composition of the PM 10 samples was determined by ion chromatography for the main ions, and, on selected samples, by particle-induced X-ray emission (PIXE) for the total content of crustal markers. Aerosol optical depth measurements were carried out in parallel to the PM 10 sampling.The average PM 10 concentration at Lampedusa over the period June 2004-December 2010 is 31.5 µg m −3 , with low interannual variability. The annual means are below the EU annual standard for PM 10 , but 9.9 % of the total number of daily data exceeds the daily threshold value established by the European Commission for PM (50 µg m −3 , European Community, EC/30/1999).The Saharan dust contribution to PM 10 was derived by calculating the contribution of Al, Si, Fe, Ti, non-sea-salt (nss) Ca, nssNa, and nssK oxides in samples in which PIXE data were available. Cases in which crustal content exceeded the 75th percentile of the crustal oxide content distribution were identified as elevated dust events. Using this threshold, we obtained 175 events. Fifty-five elevated dust events (31.6 %) displayed PM 10 higher than 50 µg m −3 , with dust contributing by 33 % on average.The crustal contribution to PM 10 has an annual average value of 5.42 µg m −3 , and reaches a value as high as 67.9 µg m −3 (corresponding to 49 % of PM 10 ) during an intense Saharan dust event.The crustal content estimated from a single tracer, such as Al or Ca, is in good agreement with the one calculated as the sum of the metal oxides. Conversely, larger crustal contents are derived by applying the EU guidelines for demonstration and subtraction of exceedances in PM 10 levels due to high background of natural aerosol. The crustal aerosol amount and contribution to PM 10 showed a very small seasonal dependence; conversely, the dust columnar burden displays an evident annual cycle, with a strong summer maximum (monthly average aerosol optical depth at 500 nm up to 0.28 in June-August). We found that 71.3 % of the dust events identified from optical properties over the atmospheric column display a high dust content at the ground level. Conversely, the remaining 28.7 % of cases present a negligible or small impact on the surface aerosol composition due to the transport processes over the Mediterranean Sea, where dust frequently travels above the marine boundary layer, especially in summer.Published by Copernicus Publications on behalf of the European Geosciences Union. M. Marconi et al.: Saharan dust aerosol over the central Mediterranean SeaBased on backward trajectories, two regions, one in Algeria-Tunisia, and one in Libya, are identified as main source areas for intense dust episodes occurring mainly in autumn and winter. Data on the bulk composition of mineral aerosol arising from these two source areas are scarce; results on characteristic ratios between ele...

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Section: Source Areas Of Saharan Dust Aerosolmentioning

confidence: 99%

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

et al. 2014

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“…LCR depends weakly on differences in dust source area and collected aerosol size fraction, contrarily to LVR, which reaches 0.9 for large (> 10 µm) particles from specific areas of the Sahara (e.g. Hoggar Massif; Henderson and Henderson, 2009;Moreno et al, 2006;Castillo et al, 2008).…”

Section: Rare Earth Elementsmentioning

confidence: 99%

Constraining the ship contribution to the aerosol of the central Mediterranean

et al. 2017

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Abstract. Particulate matter with aerodynamic diameters lower than 10 µm, (PM 10 ) aerosol samples were collected during summer 2013 within the framework of the Chemistry and Aerosol Mediterranean Experiment (ChArMEx) at two sites located north (Capo Granitola) and south (Lampedusa Island), respectively, of the main Mediterranean shipping route in the Straight of Sicily.The PM 10 samples were collected with 12 h time resolutions at both sites. Selected metals, main anions, cations and elemental and organic carbon were determined.The evolution of soluble V and Ni concentrations (typical markers of heavy fuel oil combustion) was related to meteorology and ship traffic intensity in the Straight of Sicily, using a high-resolution regional model for calculation of back trajectories. Elevated concentration of V and Ni at Capo Granitola and Lampedusa are found to correspond with air masses from the Straight of Sicily and coincidences between trajectories and positions of large ships; the vertical structure of the planetary boundary layer also appears to play a role, with high V values associated with strong inversions and a stable boundary layer. The V concentration was generally lower at Lampedusa than at Capo Granitola V, where it reached a peak value of 40 ng m −3 .Concentrations of rare earth elements (REEs), La and Ce in particular, were used to identify possible contributions from refineries, whose emissions are also characterized by elevated V and Ni amounts; refinery emissions are expected to display high La / Ce and La / V ratios due to the use of La in the fluid catalytic converter systems. In general, low La / Ce and La / V ratios were observed in the PM samples. The combination of the analyses based on chemical markers, air mass trajectories and ship routes allows us to unambiguously identify the large role of the ship source in the Straight of Sicily.Based on the sampled aerosols, ratios of the main aerosol species arising from ship emission with respect to V were estimated with the aim of deriving a lower limit for the total ship contribution to PM 10 . The estimated minimum ship emission contributions to PM 10 were 2.0 µg m −3 at Lampedusa and 3.0 µg m −3 at Capo Granitola, corresponding with 11 and 8.6 % of PM 10 , respectively.

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“…There are number of reports indicating that the surface soils in the Sahelian region to be depleted in calcite (Claquin et al, 1999;Kandler et al, 2007;Castillo et al, 2008;Formenti et al, 2008). Instead, these studies attribute Northern Sahara to be the major source when dust particles are particularly enriched in Ca.…”

Section: Origin Of Major Particlesmentioning

confidence: 99%

Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006

et al. 2010

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Abstract. In order to gain insights into the characteristics of the mineral dust particles incorporated in the actual cloud droplets and the related cloud processing, the French ATR-42 research aircraft equipped both with a counterflow virtual impactor (CVI) and community aerosol inlet was deployed in Niamey, Niger (13 • 30 N, 02 • 05 E) in August 2006 within the framework of the African Monsoon Multidisciplinary Analysis (AMMA) project.Cloud residual and clear-sky particles were collected separately and analyzed individually using a transmission electron microscope (TEM) and a scanning electron microscope coupled with an energy dispersive X-ray spectroscopy (SEM-EDX). The analysis revealed interesting characteristics on the coarse dust particles (Dp>1µm), particularly those which likely had acted as CCN.Traces of heterogeneously formed secondary sulfate, chloride and nitrate were found on many dust particles (though fraction of sulfate may be present in the form of gypsum as primary dust component). These secondary species were particularly enhanced in clouds (i.e. cloud processing). The study illustrates that calcium-rich particles assumed to be carbonates (Calcite, Dolomite) contained the secondary species in significantly larger frequency and amount than the silicates (Quartz, Feldspar, Mica, Clay), suggesting that they represent the most reactive fraction of the mineral dust. A surprisingly large fraction of the Ca-rich particles were already found in deliquesced form even in clear-sky condiCorrespondence to: A. Matsuki (matsuki@staff.kanazawa-u.ac.jp) tions, most probably reflecting their extreme hygroscopicity, resulting from their reaction with HNO 3 gas.Both silicate and Ca-rich particles were found dominant among the supermicron cloud residues, and they were supposed to be those previously activated as CCN. It is highly probable that the observed formation of soluble materials enhanced their cloud nucleating abilities.

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Trace element variation in size-fractionated African desert dusts

Cited by 128 publications

References 52 publications

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Constraining the ship contribution to the aerosol of the central Mediterranean

Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006

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Trace element variation in size-fractionated African desert dusts

Cited by 128 publications

References 52 publications

Saharan dust aerosol over the central Mediterranean Sea: PM&lt;sub&gt;10&lt;/sub&gt; chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM&lt;sub&gt;10&lt;/sub&gt; chemical composition and concentration versus optical columnar measurements

Constraining the ship contribution to the aerosol of the central Mediterranean

Cloud processing of mineral dust: direct comparison of cloud residual and clear sky particles during AMMA aircraft campaign in summer 2006

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Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements

Saharan dust aerosol over the central Mediterranean Sea: PM<sub>10</sub> chemical composition and concentration versus optical columnar measurements