27 Aug 2021

27 Aug 2021

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

Inferring iron oxides species content in atmospheric mineral dust from DSCOVR EPIC observations

Sujung Go1,2, Alexei Lyapustin2, Gregory L. Schuster3, Myungje Choi1,2, Paul Ginoux4, Mian Chin2, Olga Kalashnikova5, Oleg Dubovik6, Jhoon Kim7,8, Arlindo da Silva2, Brent Holben2, and Jeffrey S. Reid9 Sujung Go et al.
  • 1University of Maryland Baltimore County, Baltimore, MD, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 3NASA Langley Research Center, Hampton, VA, USA
  • 4Geophysical Fluid Dynamics Laboratory, Princeton, NJ, United States
  • 5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 6Laboratoire d’Optique Atmosphérique, Université de Lille-1, CNRS, Villeneuve d’Ascq, France
  • 7Yonsei University, Seoul, Korea
  • 8Particulate Matter Research Institute, Samsung Advanced Institute of Technology, Korea
  • 9US Naval Research Laboratory, Monterey, CA, USA

Abstract. The iron-oxide content of dust in the atmosphere and most notably its apportionment between hematite (α-Fe2O3) and goethite (α-FeOOH) are key determinants in quantifying dust's light absorption, its top of atmosphere UV radiances used for dust monitoring, and ultimately shortwave dust direct radiative effects (DRE). Hematite and goethite column mass concentrations and iron-oxide mass fractions of total dust mass concentration were retrieved from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) measurements in the ultraviolet–visible (UV–Vis) channels. The retrievals were performed for dust-identified aerosol plumes using aerosol optical depth (AOD) and spectral imaginary refractive index provided by the Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm over six continental regions (North America, North Africa, West Asia, Central Asia, East Asia, and Australia). The dust particles are represented as an internal mixture of non-absorbing host and absorbing hematite and goethite. We use the Maxwell–Garnett effective medium approximation with carefully selected complex refractive indices of hematite and goethite that produce mass fractions of iron oxides species consistent with in situ values found in the literature to derive the hematite and goethite volumetric/mass concentrations from MAIAC EPIC products. We compared the retrieved hematite and goethite concentrations with in situ dust aerosol mineralogical content measurements, as well as with published data. Our data display variations within the published range of hematite, goethite, and iron-oxide mass fractions for pure mineral dust cases. A specific analysis is presented for 15 sites over the main dust source regions. Sites in the central Sahara, Sahel, and Middle East exhibit a greater temporal variability of iron oxides relative to other sites. Niger site (13.52° N, 2.63° E) is dominated by goethite over Harmattan season with median of ~2 weight percentage (wt.%) of iron-oxide. Saudi Arabia site (27.49° N, 41.98° E) over Middle East also exhibited surge of goethite content with the beginning of Shamal season. The Sahel dust is richer in iron-oxide than Saharan and northern China dust except in Summer. The Bodélé Depression area shows a distinctively lower iron-oxide concentration (~1 wt. %) throughout the year. Finally, we show that EPIC data allow to constrain the hematite refractive index. Specifically, we select 5 out of 13 different number of hematite refractive indices widely variable in published laboratory studies by constraining the iron-oxide mass ratio to the known measured values. Provided climatology of hematite and goethite mass fractions across main dust regions of the Earth will be useful for dust shortwave DRE studies and climate modeling. 

Sujung Go et al.

Status: open (until 08 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-599', Anonymous Referee #1, 16 Sep 2021 reply

Sujung Go et al.


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Short summary
This paper presents a retrieval algorithm of iron oxides species (hematite, goethite) content in the atmosphere from observation of EPIC satellite instrument. Our results display variations within the published range of hematite, goethite both spatially and temporally over the main dust source regions. It implies single-viewing satellite instruments may provide essential information in shortwave dust direct radiative effects study of climate modeling.