Mineralogy of Saharan dust transported over northwestern tropical Atlantic Ocean in relation to source regions

Caquineau, Sandrine

doi:10.1029/2000jd000247

Cited by 186 publications

(214 citation statements)

References 51 publications

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“…The quantification, performed via calibration with reference standard minerals, reveals that clays account for between 80% and 90% of the dust composition, regardless of the dust origin. This estimate is in good agreement with previous results of Caquineau et al (2002) for dust aerosols originating in the Sahelian belt. Our results also corroborate indirect evidence from ground-based remote sensing of the hyperspectral infrared downwelling radiance provided by Turner (2008) and suggest that the radiative signature can be described by considering that Sahelian mineral dust is composed predominantly of clay in the form of kaolinite.…”

Section: Discussionsupporting

confidence: 92%

“…Nonetheless, this distinction is needed because of their different spectral optical properties (Sokolik and Toon, 1999). The apportionment of the total clay content into illite and kaolinite could be performed using the illite-tokaolinite (I/K) mass ratios determined by Caquineau et al (2002) for samples of equivalent origins. These authors showed that the I/K ratios vary between 0.1 for Sahelian dust to 2 for Saharan dust.…”

Section: Calculation Of the Mineralogical Compositionmentioning

confidence: 99%

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Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Klaver

Formenti

Caquineau

et al. 2011

Quart J Royal Meteoro Soc

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Regardless of origin, clays (illite, kaolinite) dominated the total volume (79-90%); the remainder was composed of quartz, calcium-rich minerals (calcite, dolomite, gypsum) and alkali feldspars. Iron oxides, measured using a selective chemical extraction method, accounted for 1-3% of the total dust mass. The dependence of particle number size and shape distribution on the origin of dust seems minor too, although our results might be slightly misleading due to the fact that those kinds of data have been gathered on flights when dust had comparable origins and residence time.Mineral dust is only weakly absorbing in the mid-visible wavelengths (single scattering albedo ω 0 > 0.95 at 550 nm), and ω 0 measured values can be reproduced by measuring the bulk fractions of the major minerals, i.e. clays, quartz, calcite and iron oxides. At this wavelength, knowledge of the nature of clays and iron oxides, or the state of mixing of the minerals, does not induce significant differences in the results. A more precise description of the nature of clays and iron oxides is necessary at lower wavelengths owing to larger differences in their spectral optical properties. In particular, knowledge of the nature of the dominant clay is important for determining light scattering in the backward hemisphere.

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Section: Discussionsupporting

confidence: 92%

Section: Calculation Of the Mineralogical Compositionmentioning

confidence: 99%

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Klaver

Formenti

Caquineau

et al. 2011

Quart J Royal Meteoro Soc

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“…Low K/Ch ratio (below than 1) show that the dust is originated from an Eastern Asian source. On the other hand, Saharan and North American dusts are characterized by abundance of kaolinite compared to chlorite, leading to higher K/Ch ratios (ranging from 1 to 10) (Caquineau et al 2002). In fact, as it is shown on Table 5, all collected dust samples, were originated from the North Africa region and contained higher quantities of kaolinite than chlorite (ratios between 1.1 and 2.7), with a mean K/Ch ratio value equal to 1.8 ± 0.8.…”

Section: Mineralogical Analysismentioning

confidence: 99%

Ambient Particulate Matter Concentration Levels and their Origin During Dust Event Episodes in the Eastern Mediterranean

et al. 2018

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The eastern Mediterranean region is strongly influenced by long-range transported particulate matter such as desert dust from northern Africa. To investigate the dynamics of Saharan dust events and their origin, satellite images from the MODIS spectroradiometer of NASA's satellites Terra and Aqua, and back trajectories analysis of the HYSPLIT model were combined together with continuous ground-based field data. Field PM 10 and PM 2.5 measurements were performed in the period 2003-2013 at the Akrotiri monitoring station on the island of Crete (Greece). Furthermore, the mineralogical composition of a small number of samples was determined by X-ray powder diffraction, whereas elemental particle composition analysis was performed on the dust samples collected using the ICP-MS technique for a series of elements. The annual average percentage of days with Sahara dust outbreaks in the region of western Crete (Akrotiri station) was 9.3% for the period 2003-2013. Excluding the PM 10 exceedances caused by Sahara dust events, the average PM 10 monthly concentrations are decreased by 20.5% during the 8-month period November-June, with higher PM 10 concentration reduction (29.9%) in the period February-April. Mineralogical analysis showed that illite was the most abundant mineral identified in all samples, followed by quartz and calcite. Gypsum was detected only in the dry sample. Moreover, the elemental particle composition analysis showed that collected dust originated from Africa deserts.

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“…Relative percentages in mass for kaolinite, illite and quartz are respectively 71.6, 9.1 and 19.3, as derived from measurements performed at Banizoumbou (Caquineau, 1997). The ratio between relative abundance of illite and kaolinite is 0.1 which is typical to Sahelian regions (Caquineau et al, 2002).…”

Section: The Modtran-41 Radiative Transfer Modelmentioning

confidence: 97%

“…The IDDI has been employed to the study of various applications including dust climatology (Brooks and Legrand, 2000), sources (Léon and Legrand, 2003), transport (Petit et al, 2005), composition (Caquineau et al, 2002); to validation of dust emission modeling (Marticorena et al, 1997) and of satellite desert surface mapping (Marticorena et al, 2004). Because the AOT is the most popular measure of the aerosol amount, the IDDI index is compared to it.…”

Section: Introductionmentioning

confidence: 99%

Improvement of the detection of desert dust over the Sahel using METEOSAT IR imagery

et al. 2006

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Abstract.Desert dust over the arid regions of Africa is detected using the Infrared Difference Dust Index (IDDI) derived from the thermal infrared (TIR) channel of METEOSAT. However, the comparison with photometric aerosol optical thickness (AOT) of this dust index reveals some discrepancies. Using an instrumented site in Sahel where aerosol properties and meteorological conditions were monitored daily during the dry season, we performed radiative transfer computations with the MODTRAN 4.1 code to develop a method to improve the IDDI usefulness. We found that discrepancies between AOT and IDDI variations mostly come from changes in the surface temperature (T s ), which is an important parameter for radiative transfer computations in the TIR. We show that this temperature varies from day to day with the surface wind speed and during the course of the season with the solar elevation, and that it is possible, for the site considered, to correct T s from these combined effect using a simple parameterization. We also observe that the dust layer itself has an impact on T s by reducing the amount of solar radiation at the surface, and that this phenomenon can also be accounted for by adding an AOT-dependence to the above parameterization of T s . We show that this parameterization allows improving the agreement between the IDDI and the photometric AOT.

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Mineralogy of Saharan dust transported over northwestern tropical Atlantic Ocean in relation to source regions

Cited by 186 publications

References 51 publications

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Ambient Particulate Matter Concentration Levels and their Origin During Dust Event Episodes in the Eastern Mediterranean

Improvement of the detection of desert dust over the Sahel using METEOSAT IR imagery

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