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Rapid changes of dust geochemistry in the Saharan Air Layer linked to sources and meteorology
Title: Rapid changes of dust geochemistry in the Saharan Air Layer linked to sources and meteorology
Authors: Rodríguez González, Sergio ORCID RESEARCHERID Autor AEMETCalzolai, GiuliaChiari, MassimoNava, SilviaGarcía Álvarez, María IsabelLópez Solano, Javier ORCID RESEARCHERID Autor AEMETMarrero, CarlosAutor AEMETLópez-Darias, JessicaCuevas Agulló, Emilio ORCID RESEARCHERID SCOPUSID Autor AEMETAlonso Pérez, SilviaPrats Porta, Natalia ORCID RESEARCHERID Autor AEMETAmato, FulvioLucarelli, FrancoQuerol, Xavier
Keywords: Saharan Air Layer; Saharan dust sources; Dust geochemistry; North Africa; Harmattan; NAFDI
Issue Date: 2019
Publisher: Elsevier
Citation: Atmospheric Environment. 2019
Publisher version:
Abstract: Based at Izaña Observatory (∼2400 m a.s.l. in Tenerife), we performed 1-h resolution measurements of elemental composition of dust in the Saharan Air Layer (SAL) and studied the variability of the ratios of these elements to aluminium (elemental ratios). In a period (∼1 week) of continuous dust presence (50–200 μg/m3), we observed rapid variations of dust composition; some elemental ratios changed by a factor 2 in a few (5–8) hours. The lowest variability (Normalized Variability Range, %) was found for Si/Al (9%) and Fe/Al (9%), followed by the ratios of K, Ti, Mg, Mn, Ca and Sr to Al (20–80%), and the highest for S/Al, Na/Al and Cl/Al (110–160%) and a number of trace metals (Cr, Cu, Ni, Zn, Zr) and Br (>200%). This variability was induced by the alternating impacts of three of the large North African dust sources: NE Algeria (rich in evaporite minerals bearing Ca, S, Sr, K and Mg and in illite mineral), Western Sahara to Bechar region (containing Na, S and Cl rich Yermosol soils) and SW Sahara – Western Sahel (rich in illite and hematite). We traced the variability in large-scale meteorology using the so-called North African Dipole Intensity (NAFDI: strength of the subtropical Saharan high -Morocco-to the monsoon tropical low -Nigeria-). The mobilization of dust from the different sources was associated with westward propagating Harmattan pulses linked to the change of phase of NAFDI (- to +), the associated westward shifts of the Saharan Heat Low and convective monsoon inflow. We found a correlation between dust composition in the SAL and NAFDI: moderate NAFDI values (0 to +2.5) were associated with Ca, K, Na, Mg and S rich dust linked to dust sources in NE Algeria, whereas higher NAFDI values (+2.5 to +4) were linked to Fe rich dust (Ca, Na and S depleted) linked to dust sources in SW Sahara – Western Sahel. The results of this study also show that some trace elements (Br, Cr, Ni, Zn and Zr) are influenced by industrial emissions into North Africa.
Sponsorship : This study was performed within the project VARDUST-SAL (PGC 2018-099166-B-I00), funded by the Ministry of Science, Research and Innovation of Spain, the Research State Agency of Spain and the European Regional Development Fund (ERDF).
ISSN: 1352-2310
Appears in Collections:Artículos científicos 2019-2022

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