Preprints
https://doi.org/10.5194/amt-2021-431
https://doi.org/10.5194/amt-2021-431

  23 Dec 2021

23 Dec 2021

Review status: this preprint is currently under review for the journal AMT.

Contrasting Mineral Dust Abundances from X-Ray Diffraction and Reflectance Spectroscopy

Mohammad R. Sadrian, Wendy M. Calvin, and John McCormack Mohammad R. Sadrian et al.
  • Department of Geological Sciences and Engineering, University of Nevada, Reno, Reno, 89557, USA

Abstract. Mineral dust particles dominate aerosol mass in the atmosphere and directly modify Earth’s radiative balance through absorption and scattering. This radiative forcing varies strongly with mineral composition, yet there is still limited knowledge on the mineralogy of atmospheric dust. In this study, we performed X-ray diffraction (XRD) and reflectance spectroscopy measurements on 37 different atmospheric dust samples collected as airfall in an urban setting to determine mineralogy and the relative proportions of minerals in the dust mixture. Most commonly, XRD has been used to characterize dust mineralogy; however, without prior special sample preparation, this technique is less effective for identifying poorly crystalline or amorphous phases. In addition to XRD measurements, we performed visible, near-infrared, and short-wave infrared (VNIR/SWIR) reflectance spectroscopy for these natural dust samples as a complementary technique to determine minerology and mineral abundances. Reflectance spectra of dust particles are a function of a nonlinear combination of mineral abundances in the mixture. Therefore, we used a Hapke radiative transfer model along with a linear spectral mixing approach to derive relative mineral abundances from reflectance spectroscopy. We compared spectrally derived abundances with those determined semi-quantitatively from XRD. Our results demonstrate that total clay mineral abundances from XRD are correlated with those from reflectance spectroscopy and follow similar trends; however, XRD underpredicts the total amount of clay for many of the samples. On the other hand, calcite abundances are significantly underpredicted by SWIR compared to XRD. This is caused by the weakening of absorption features associated with the fine particle size of the samples, as well as the presence of dark non-mineral materials (e.g., asphalt) in these samples. Another possible explanation for abundance discrepancies between XRD and SWIR is related to the differing sensitivity of the two techniques (crystal structure vs chemical bonds). Our results indicate that it is beneficial to use both XRD and reflectance spectroscopy to characterize airfall dust, because the former technique is good at identifying and quantifying the SWIR-transparent minerals (e.g., quartz, albite, and microcline), while the latter technique is superior for determining abundances for clays and non-mineral components.

Mohammad R. Sadrian et al.

Status: open (until 09 Feb 2022)

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Mohammad R. Sadrian et al.

Mohammad R. Sadrian et al.

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Short summary
Mineral dust particles originate from surface soils, primarily in arid regions. They can stay suspended in the atmosphere, impacting Earth's radiation budget. Dust particles will have different perturbation effects, depending on their composition. We obtained compositional information of dust collected in an urban setting using two different techniques. We recommended using the combination of measurements to determine the variability of dust mineral abundances.