Role of clay minerals in the formation of atmospheric aggregates of Saharan dust

Cuadros, Javier; Díaz-Hernández, José Luis; Navas, Ana; Garcia‐Casco, Antonio

doi:10.1016/j.atmosenv.2015.08.077

Cited by 20 publications

(11 citation statements)

References 35 publications

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“…It could be argued that the larger particles observed here may result from aggregation phenomena taking place after in-cloud and/or below-cloud scavenging during the red rain event (Mahowald et al, 2014) or during drying of the deposited red rain. Coarsening due to aggregation of Saharan dust particles scavenged within cloud droplets followed by drying prior to dry deposition has been claimed responsible for the formation of the so-called "iberulites" (Cuadros et al, 2015;Díaz-Hernández and Párraga, 2008;Díaz-Hernández and Sánchez-Navas, 2016). Iberulites are nearly spherical, clay-rich giant particles (∼ 100 µm in diameter) that are dry deposited in Spain typically during summer Saharan dust events.…”

Section: Textural Features Of Saharan Dust: Fesem Psdmentioning

confidence: 99%

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

2018

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Abstract. The mineralogy and physicochemical features of Saharan dust particles help to identify source areas and determine their biogeochemical, radiative, and health effects, but their characterization is challenging. Using a multianalytical approach, here we characterized with unprecedented level of detail the mineralogy and physicochemical properties of Saharan dust particles massively wet deposited ( ∼ 18 g m−2) following an extreme red rain event triggered by a northern African cyclone that affected the southern Iberian Peninsula during 21–23 February 2017. Abundant palygorskite and illite, and relatively high carbonate contents, well-known northern and north-western Saharan dust indicators, along with low chlorite content and significant amounts of smectites and kaolinite, whose abundance increases southwards in the western Sahara, complemented by satellite imagery and back/forward trajectories, show that the most probable dust source areas were (i) southern/central Algeria, northern Mali, and northwestern Niger, and (ii) northern Algeria, southern Tunisia, and northwestern Libya. Scanning and transmission electron microscopy analyses, including Z-contrast high angle annular dark field (HAADF) imaging and analytical electron microscopy (AEM), show that clay minerals include abundant structural Fe (55 % of the total Fe) and typically form nanogranular aggregates covered or interspersed with amorphous/poorly crystalline iron oxyhydroxide nanoparticles (ferrihydrite), which account for ∼ 18 % of the free Fe, the rest being goethite and hematite. These nanogranular aggregates tend to form rims lining large silicate and carbonate particles. Such internally mixed iron-containing phases are the main contributors to the observed absorption of solar and thermal radiation, and along with the abundant coarse/giant particles ( > 10 µm) strongly affect the dust direct radiative forcing. The lack of secondary sulfates in aggregates of unaltered calcite internally mixed with clays/iron-rich nanoparticles shows that iron-rich nanoparticles did not form via atmospheric (acid) processing but were already present in the dust source soils. Such iron-rich nanoparticles, in addition to iron-containing clay (nano)particles, are the source of the ∼ 20 % soluble (bioavailable) iron in the studied desert dust. The dust particles are a potential health hazard, specifically the abundant and potentially carcinogenic iron-containing palygorskite fibers. Ultimately, we show that different source areas are activated over large desert extensions, and large quantities of complex dust mixtures are transported thousands of kilometers and wet-deposited during such extreme events, which dwarf any other Saharan dust event affecting southwestern Europe. The past, present, and future trends, as well as impacts, of such extreme events must be taken into account when evaluating and modeling the manifold effects of the desert dust cycle.

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Section: Textural Features Of Saharan Dust: Fesem Psdmentioning

confidence: 99%

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

2018

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“…90 Ma) as the host bauxites, finally testifying that part of the source material consisted of pyroclastic ashes derived from a volcanism coeval with the formation of bauxites [9]. At the same time, the additional occurrence of zircons with Pan-African ages do not exclude that part of the parent material consisted of eolian sands carried by winds from the African craton, in a similar way to the modern Saharan eolian dust, which is transported to great distances in Europe and also in North America [69]. The discovery of fine-grained detrital minerals in the Abruzzi bauxites (e.g., zircon, ilmenite, rutile, baddeleyite) supports a similar origin also for the parent material of the Abruzzi bauxite.…”

Section: Comparison With Other Bauxite Deposits Of the Tethyan Realmmentioning

confidence: 99%

Geochemical Characterization of Bauxite Deposits from the Abruzzi Mining District (Italy)

Putzolu¹,

Papa²,

Mondillo³

et al. 2018

Minerals

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Abstract:The Abruzzi bauxite district includes the deposits located on the Campo Felice plateau and those of the Monti d'Ocre, which had been mined in the first part of the 20th century. Bauxite is of the karst type, with textures ranging between oolitic and oolitic-conglomeratic, the latter suggesting a partial reworking of evolved lateritic soils. The high contents of Al 2 O 3 and Fe 2 O 3 (average values 53.76 and 21.76 wt %, respectively) are associated with the presence of boehmite, hematite, and minor goethite. SiO 2 and TiO 2 have average values of 7.79 and 2.75 wt %, corresponding to the presence of kaolinite, anatase and rutile. Among the minor so-called "bauxitophile" elements V, Co, Ni, Cr and Zr, the most enriched is Cr, with an average value of 0.07 wt %. Nickel has an average value of 210.83 ppm. Vanadium shows an average value of 266.57 ppm, whereas the average Co concentration is 35.89 ppm. The total rare earth elements (REE) concentration in the sampled bauxite sites is variable between ca. 700 and 550 ppm. Among REEs, the most abundant element is Ce, with Ce anomalies commonly associated with authigenic REE-fluoro-carbonates, probably produced after the REEs remobilization from primary detrital minerals and their precipitation in neo-formed phases during the bauxitization process. Scandium and Ga occur in small amounts (57 and 60 ppm, respectively), but geochemical proxies of their remobilization and uptake in neo-formed minerals (Feand Al-(hydr)oxides, respectively) have been observed. The mean Eu/Eu* and Al 2 O 3 /TiO 2 ratios and the Ni-Cr contents of the Abruzzi bauxites suggest that the parent rock of these deposits was a material of acid affinity, likely corresponding to volcanic tephra or eolic loess-type sands.

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“…It is known that the certain types of aerosols such as smoke from biomass burning and urban and industrial air pollution act as small cloud‐condensation nuclei (CCN), which increase cloud albedo and in turn inhibit precipitation from clouds [ Rosenfeld , ]. The occurrence of soot aerosol and sulphur in the iberulites suggests a wet scavenging of the air pollutant, because these aggregates are generated by the interaction of dust aerosol and water droplet, presumably close to the reception area [ Cuadros et al , ]. A clay content of around 50% was measured in iberulites collected in the Granada basin, which is significantly higher than 30% found in the total dust [ Cuadros et al , ].…”

Section: Discussionmentioning

confidence: 99%

Saharan dust outbreaks and iberulite episodes

Díaz-Hernández

Navas

2016

JGR Atmospheres

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Mineral dust aerosols coming from the arid and semiarid regions of the world can aggregate and form microspherulites under special atmospheric conditions. This is the case for iberulites, formed in the atmosphere from Saharan dust intrusions into the southern Iberian Peninsula during the summer, prompting a noteworthy case of dust accretion unique in the world. This study consists of a long‐term monitoring of Saharan dust outbreaks producing haze that reaches the southern Iberian Peninsula. Aerosol concentration, relative humidity, and temperature time series available at the ground stations in this area indicate sharp variations of these atmospheric variables during the iberulite‐forming events. Most of these events occurred during the summer (60%), with 65 episodes for the period 2005–2013, in which 107 plumes reached the Iberian Peninsula. Iberulite episodes lasted 5 days on average, during which an initial increase of particulate matter (PM) levels and temperature, accompanied by a decrease in relative humidity, was registered until the third day. These trends reversed when the plume began to abate. Our data also indicate that iberulites form during dusty episodes when a minimum threshold in the content of large aerosol particles (PM10) reached concentrations above 15 µg × m−3. Surface evaporation due to the sharply rising air temperatures give rise to clouds associated with the plume, where the water droplets that formed from condensation capture large amounts of aerosols as they fall. In this sense, muddy raindrop impacts with variable water:dust ratios recorded during red‐rain episodes are interpreted as the precursor of the iberulites. A singular process of dust aggregation is here proposed for the formation of iberulites.

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Role of clay minerals in the formation of atmospheric aggregates of Saharan dust

Cited by 20 publications

References 35 publications

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Geochemical Characterization of Bauxite Deposits from the Abruzzi Mining District (Italy)

Saharan dust outbreaks and iberulite episodes

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