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The structural properties of the Saharan air layer (SAL) including chemical, morphological and optical properties were measured during the Saharan Aerosol Longrange TRansport and Aerosol Cloud interaction Experiment (SALTRACE- June/July 2013). Flight measurements were done from Cape Verde and the Caribbean. Changes happening with the chemical composition, mixing, shape and absorption of aerosol single particles (particle diameter range 0.5–3.0 µm) inside SAL during its transport are detailed. Dust-dominated SAL (relative number abundance >90%) and generally low mixing (

Understanding the effect of dust upon climate and ecosystems needs comprehensive analyses of the physiochemical properties of dust-emitting sediments in arid regions. Here, we analyse a diverse set of crusts and aeolian ripples (n=55) from various dust-hotspots within the Mojave Desert, California, USA, with focus on their particle size distribution (PSD), mineralogy, aggregation/cohesion state and iron mode of occurrence characterization. Our results showed differences in fully and minimally dispersed PSDs, with crusts average median diameters (92 and 37 µm, respectively) compared to aeolian ripples (226 and 213 µm, respectively). Mineralogical analyses unveiled variations between crusts and ripples, with crusts enriched in phyllosilicates (24 vs 7.8 %), carbonates (6.6 vs 1.1 %), Na salts (7.3 vs 1.1 %) and zeolites (1.2 and 0.12 %), while ripples enriched in feldspars (48 vs 37 %), quartz (32 vs 16 %), and gypsum (4.7 vs 3.1 %). Bulk Fe content analyses indicate higher concentrations in crusts (3.0±1.3 wt %) compared to ripples (1.9±1.1 wt %), with similar Fe speciation proportions; nano Fe-oxides/readily exchangeable Fe represent ~1.6 %, hematite/goethite ~15 %, magnetite/maghemite ~2.0 % and structural Fe in silicates ~80 % of the total Fe. We identified segregation patterns in PSD and mineralogy differences within the Mojave basins, influenced by sediment transportation dynamics and precipitates due to groundwater table fluctuations. Mojave Desert crusts show similarities with previously sampled crusts in the Moroccan Sahara for PSD and readily exchangeable Fe, yet exhibit differences in mineralogical composition, which could influence the emitted dust particles characteristics. [ABSTRACT FROM AUTHOR]

The mineralogical composition of airborne dust particles is an important but often neglected parameter for several physiochemical processes, such as atmospheric radiative transfer and ocean biochemistry. We present the development of the METAL-WRF module for the simulation of the composition of desert dust minerals in atmospheric aerosols. The new development is based on the GOCART-AFWA dust module of WRF-Chem. A new wet deposition scheme has been implemented in the dust module alongside the existing dry deposition scheme. The new model includes separate prognostic fields for nine (9) minerals: illite, kaolinite, smectite, calcite, quartz, feldspar, hematite, gypsum, and phosphorus, derived from the GMINER30 database and also iron derived from the FERRUM30 database. Two regional model sensitivity studies are presented for dust events that occurred in August and December 2017, which include a comparison of the model versus elemental dust composition measurements performed in the North Atlantic (at Izaña Observatory, Tenerife Island) and in the eastern Mediterranean (at Agia Marina Xyliatos station, Cyprus Island). The results indicate the important role of dust minerals, as dominant aerosols, for the greater region of North Africa, South Europe, the North Atlantic, and the Middle East, including the dry and wet depositions away from desert sources. Overall, METAL-WRF was found to be capable of reproducing the relative abundances of the different dust minerals in the atmosphere. In particular, the concentration of iron (Fe), which is an important element for ocean biochemistry and solar absorption, was modeled in good agreement with the corresponding measurements at Izaña Observatory (22% overestimation) and at Agia Marina Xyliatos site (4% overestimation). Further model developments, including the implementation of newer surface mineralogical datasets, e.g., from the NASA-EMIT satellite mission, can be implemented in the model to improve its accuracy. [ABSTRACT FROM AUTHOR]

• Geochemistry and mineralogy successfully separated dust sources across western US. • Across-site variability was more important than seasonal variability. • Playa dust was easily recognizable based on its distinct mineralogy and geochemistry. • Additional tracers needed to distinguish rangeland and grazing sites. • Linear discriminant analysis is a useful, but underutilized, dust fingerprinting tool. Dust events originate from multiple sources in arid and semi-arid regions, making it difficult to quantify source contributions. Dust geochemical/mineralogical composition, if the sources are sufficiently distinct, can be used to quantify the contributions from different sources. To test the viability of using geochemical and mineralogical measurements to separate dust-emitting sites, we used dust samples collected between 2018 and 2020 from ten National Wind Erosion Research Network (NWERN) sites that are representative of western United States (US) dust sources. Dust composition varied seasonally at many of the sites, but within-site variability was smaller than across-site variability, indicating that the geochemical signatures are robust over time. It was not possible to separate all the sites using commonly applied principal component analysis (PCA) and cluster analysis because of overlap in dust geochemistry. However, a linear discriminant analysis (LDA) successfully separated all sites based on their geochemistry, suggesting that LDA may prove useful for separating dust sources that cannot be separated using PCA or other methods. Further, an LDA based on mineralogical data separated most sites using only a limited number of mineral phases that were readily explained by the local geologic setting. Taken together, the geochemical and mineralogical measurements generated distinct signatures of dust emissions across NWERN sites. If expanded to include a broader range of sites across the western US, a library of geochemical and mineralogical data may serve as a basis to track and quantify dust contributions from these sources. [ABSTRACT FROM AUTHOR]

We investigated the variation in the mineralogical composition of surface soil samples from a wide range of atmospheric dust aerosol generating regions. These soils likely have mineral compositions similar to dust aerosols. We measured the visible, shortwave infrared (VSWIR) and long wave infrared (LWIR) reflectance spectra, as well as LWIR transmission spectra and carried out linear spectral mixture modeling on the transmission data. The spectroscopically identified minerals were compared with the mineralogy previously obtained using X‐ray diffraction (XRD) and optical microscopy (OM). The results showed that VSWIR is very sensitive to iron‐bearing minerals and better identifies their presence and type compared to XRD and OM. Clay minerals and carbonates have multiple distinct absorptions features in SWIR but are often overlapping, limiting our ability to uniquely assign spectral features. LWIR reflectance easily distinguishes carbonates, even in trace amounts that were not identified with other techniques. LWIR reflectance spectra for silicates were more complicated to interpret. In some samples, we were able to identify Si‐O features diagnostic of common silicates; however, in most cases these features were absent, and an unusual new peak (∼7.4–7.9 μm) was observed. LWIR transmission is characterized by strong absorption that arises from overlapping features from multiple silicate minerals, but carbonates are readily identifiable. Spectroscopy is complementary to XRD and can help identify additional minerals in these soil samples. Our results can help improve global soil atlases and can be used to support interpretation and validation of data acquired by current and future remote sensing instruments. Plain Language Summary: We measured global surface soils, whose composition is likely similar to atmospheric dust aerosols, in visible, shortwave and longwave infrared reflectance and transmission to determine their mineralogy. Spectroscopy is complementary to other techniques and often better identified specific minerals in these samples. These measurements can be used to improve global soil atlases and to support interpretation of data from current and future remote sensing instruments. Key Points: Global mineral dust aerosols have diverse mineralogy with complex spectral propertiesCoated grains and intimately mixed fine‐grained minerals have a large effect on the spectral characteristics of global dust aerosolsSpectral measurements of global parent soils can improve global soil atlases and validate data from Earth Surface Mineral Dust Source Investigation [ABSTRACT FROM AUTHOR]

Abstract Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-containing dust, which is easily transported by wind to the surrounding environment. To assess the human exposure to dust-derived metal(loid)s (As, Cd, Cu, Pb, Sb, Zn), as well as the potential risks related to incidental dust ingestion, we studied mine tailing dust (n = 8), slag dust (n = 5) and smelter dust (n = 4) from old mining and smelting sites in northern Namibia (Kombat, Berg Aukas, Tsumeb). In vitro bioaccessibility testing using extraction in simulated gastric fluid (SGF) was combined with determination of grain-size distributions, chemical and mineralogical characterizations and leaching tests conducted on original dust samples and separated PM 10 fractions. The bulk and bioaccessible concentrations of the metal(loid)s were ranked as follows: mine tailing dusts < slag dusts ≪ smelter dusts. Extremely high As and Pb bioaccessibilities in the smelter dusts were caused by the presence of highly soluble phases such as arsenolite (As 2 O 3) and various metal-arsenates unstable under the acidic conditions of SGF. The exposure estimates calculated for an adult person of 70 kg at a dust ingestion rate of 50 mg/day indicated that As, Pb (and also Cd to a lesser extent) grossly exceeded tolerable daily intake limits for these contaminants in the case of slag and smelter dusts. The high risk for smelter dusts has been acknowledged, and the safety measures currently adopted by the smelter operator in Tsumeb are necessary to reduce the staff's exposure to contaminated dust. The exposure risk for the local population is only important at the unfenced disposal sites at Berg Aukas, where the PM 10 exhibited high levels of bioaccessible Pb. Graphical abstract Unlabelled Image Highlights • Large amounts of dust in old mining sites in semi-arid areas of northern Namibia • Multi-method dust characterization for elucidation of metal(loid) binding/release • Metal(loid) bioaccessibility increase for mine tailings < slags ≪ smelter dusts • Highest risks of As, Pb (and Cd) intake for smelter-derived dusts [ABSTRACT FROM AUTHOR]

This paper promotes an understanding of the mineralogical, chemical, and physical interrelationships of re-suspended mineral dusts collected as grab samples from global dust sources. Surface soils were collected from arid regions, including the southwestern USA, Mali, Chad, Morocco, Canary Islands, Cape Verde, Djibouti, Afghanistan, Iraq, Kuwait, Qatar, UAE, Serbia, China, Namibia, Botswana, Australia, and Chile. The < 38 µm sieved fraction of each sample was re-suspended in a chamber, from which the airborne mineral dust could be extracted, sampled, and analyzed. Instruments integrated into the entrainment facility included two PM10 and two PM2.5 filter samplers, a beta attenuation gauge for the continuous measurement of PM10 and PM2.5 particulate mass fractions, an aerodynamic particle size (APS) analyzer, and a three wavelength (405, 532, 781 nm) photoacoustic instrument with integrating reciprocal nephelometer for monitoring absorption and scattering coefficients during the dust re-suspension process. Filter sampling media included Teflon® membrane and quartz fiber filters for chemical analysis, and Nuclepore® filters for individual particle analysis by Scanning Electron Microscopy (SEM). The < 38 µm sieved fractions were also analyzed by X-ray diffraction for their mineral content while the > 75 µm, < 125 µm soil fractions were mineralogically assessed by optical microscopy. Presented here are results of the optical measurements, showing the interdependencies of single scattering albedos (SSA) at three different wavelengths and chemical as well as mineralogical content of the entrained dust samples. Relationships between the SSA of airborne dusts, and iron (Fe) in hematite, goethite, and clay minerals (montmorillonite, illite, palygorskite) are demonstrated. Differences in clay mineralogy between samples from Mali and those from other localities are highlighted. Results from this study can be integrated into a database of mineral dust properties, for applications in climate modeling, remote sensing, visibility, health (medical geology), ocean fertilization, and impact on equipment. [ABSTRACT FROM AUTHOR]

Abstract: A fine grained magnetic iron oxide precipitate found in Denmark has been studied with regard to grain size, magnetic properties, aerosol transport, grain electrification, aggregation and optical reflectance. It has shown itself to be a good Martian dust analogue. The fraction of the Salten Skov I soil sample <63μm was separated from the natural sample by dry sieving. This fraction could be dispersed by ultrasonic treatment into grains of diameter ∼1μm, in reasonable agreement with suspended dust grains in the Martian atmosphere estimated from the Viking, Pathfinder and Mars Exploration Rover missions. Though mineralogical and chemical differences exist between this analogue and Martian dust material, in wind tunnel experiments many of the physical properties of the atmospheric dust aerosol are reproduced. [Copyright &y& Elsevier]

Abstract: The island of Gran Canaria is located in the eastern Atlantic, to the west of the Saharan Desert, and, as a result of its proximity, is regularly affected by Saharan dust. When this weather condition occurs (haze conditions) the particulate/aerosol accumulation rate was lightly higher than under non-haze conditions (5.4±3.8mgm−2 h−1 versus 4.3±2.1mgm−2 h−1). To quantify the contribution of airborne Saharan dust to soil development in northeastern Gran Canaria, aeolian dust was collected weekly at different altitudes and distances from the coast during a year in a series of collection plots. Mean values of dust accumulation rates decreased with increasing altitude (from 79 to 17gm−2 yr−1). The mineralogy of airborne dust, identified by XRD, was quartz, Mg-calcite, calcite, feldspars, dolomite, magnetite, aragonite, halite, and minor amounts of illite, kaolinite-chlorite and palygorskite. Quartz is considered allochthonous because it is not present in the volcanic substrate of the island. However, the difference in quartz concentration from haze to non-haze conditions was only 10% higher. This suggests an external source, but does not preclude a recycled origin. The recognition of well shaped dolomites, observed by SEM-EDX in collected dust samples and in soils samples of the lowest altitude plot, indicate an edaphic origin, but are later recycled as an airborne component. [Copyright &y& Elsevier]

Africa is the great source of airborne dust, and a very large proportion of it blows out of the Lake Chad basin. There are various types of dust, an initial simple division might be into large dust and small dust, but the small dust category is itself divided into essentially monomineralic dust and clay mineral agglomerate (CMA) dust. The monomineralic dust populations are separated by Tanner gaps. Long weathering times allow small CMA dust particles to be produced (the P1 process); the initial transportation processes (T1) have led to the vast accumulation of dust material in the Lake Chad basin. These early processes are important in the study of African dust. Ground material controls the nature of the dust cloud. Small dust is essentially old dust; large dust is young dust, and the two form distinct populations. CMA dust derived directly from old lake basins is basically controlled by the nature of the lake sediment. A simple Monte Carlo model shows how particle packing parameters control the size of small CMA dust, limiting it to the very fine silt fraction. [Copyright &y& Elsevier]

Dust deposition over the Dead Sea has been studied for 3 years (1997–1999) using two collectors installed on a buoy anchored 3·5 km off-shore, south-east of Ein-Gedi. Deposition rates ranged between lows during winter (6·7–15·2 g m−2 year−1) and summer (11·4–24·7 g m−2 year−1) and highs in spring (35·7–120·7 g m−2 year−1) and autumn (39·1–158·3 g m−2 year−1). Most of the deposition was in the form of pulses, generated by dust storms. A gradual increase in yearly deposition was observed from 255 kg ha−1 in 1997, to 605 kg ha−1 in 1999. The particle-size distribution is distinctly unimodal, with the mode close to 10 μm and is not season related. This distribution suggests that the dust had been transported from medium to long range and differs markedly from that of land based collectors, where the distribution curve is bimodal, indicating the presence of material of local origin. The deposit consists of soluble salts, carbonates, quartz, and aluminosilicates, principally feldspars and clay minerals.Soluble cations and anions, including bromide, are all related to Dead Sea water, except for nitrates which are of anthropogenic origin. Some of the sulphate may be air-borne gypsum. Calcite contents vary between 5·2% and 33·1%, dolomite in the range of 1·5–14·8%. The calcite/dolomite ratio rises with the rise in the deposition rate. Apatite is present in the range of 1–5% and apparently is season related. Small amounts of phosphate appear to be related to the frequency of winds blowing from a phosphate-mining area about 45 km away. Clay minerals include smectite, kaolinite, illite and minor amounts of palygorskite and differ distinctly from that of North-African Harmattan dust. The overall mineral composition of dust over the Dead Sea shows no relation to west and north Saharan dusts and suggests an origin principally in the Negev, Egyptian and Lybian deserts. [Copyright &y& Elsevier]

Exposure to dust particles enriched with arsenic (As) is a significant health threat for populations living in Southeast Asian megacities. The mineralogical composition of dust particles is the key factor that controls the retention and release of As. This study investigated the degree of metal(oid)s pollution (As, Ca, Fe, K, Ga, Rb, Sr, Ti, V, Y, and Zr) in road dust of Dhaka city, Bangladesh. Enrichment factor and geoaccumulation index suggested that the road dust was heavily enriched with As, which triggers a comprehensive investigation of its controlling mechanisms and potential health risks by combining physicochemical and mineralogical information with multivariate analysis and a simulated probabilistic risk estimation model. Alkaline road dust (pH 1:5 ranges from 8.02 to 10.34) in Dhaka city was found to have significant enrichment of As. Dust alkalinity was possibly controlled by the presence of carbonate minerals, such as calcite. Quartz was identified as the dominant mineral phase followed by magnesium carbon arsenide (MgCAs 2 ). Carbonate mineral driven alkaline pH conditions in road dust would potentially trigger the release and mobilization of As to the environment. However, organic complexation can stabilize As on particle surfaces. Monte Carlo simulation-based health risk forecast suggested that the probability of As associated cancer risk has greatly exceeded the threshold value of 1E-4 for adults and children, and children are more vulnerable than adults. According to sensitivity analysis, the concentration of As and exposure duration (ED) posed the most significant impact (>58%) on risk estimation., (Copyright © 2021 Elsevier Ltd. All rights reserved.)