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https://doi.org/10.5194/egusphere-2025-3512
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-3512
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
30 Jul 2025
| 30 Jul 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
Mid- and Far-Infrared Spectral Signatures of Mineral Dust from Low- to High-Latitude Regions: significance and implications
Abstract. Mineral dust absorbs and scatters solar and infrared radiation, thereby affecting the radiance spectrum at the surface and top-of-atmosphere and the atmospheric heating rate. While half of the outgoing thermal radiation is emitted in the far infrared (FIR, 15–100 μm), knowledge of the optical properties and thermal radiative effects of dust is currently limited to the mid-infrared region (MIR, 3–15 μm). In this study we performed pellet spectroscopy measurements to evaluate the MIR and FIR contribution to dust absorbance and explore the variability and spectral diversity of the dust signature within the 2.5–25 μm range. Thirteen dust samples re-suspended from parent soils with contrasting mineralogy were investigated, including low and mid latitude dust (LMLD) sources in Africa, America, Asia, and Middle East, and high latitude dust (HLD) from Iceland. Results show that the absorbance of dust in the FIR up to 25 μm is comparable in intensity to that in the MIR. Also, spectrally different absorption (position and shape of the peaks) is observed for HLD compared to LMLD, due to differences in mineralogical composition. Corroborated with the few available literature data on absorption properties of natural dust and single minerals up to 100 μm wavelength, these data suggest the relevance of MIR and FIR interactions to the dust radiative effect for low to high latitude sources. Furthermore, the dust spectral signatures in the MIR and FIR could potentially be used to characterise the mineralogy and differentiate the origin of airborne particles based on infrared remote sensing observations.
How to cite. Di Biagio, C., Bru, E., Orta, A., Chevaillier, S., Baldo, C., Bergé, A., Cazaunau, M., Lafon, S., Nowak, S., Pangui, E., Andreae, M. O., Dagsson-Waldhauserova, P., Dintwe, K., Kandler, K., King, J. S., Chaput, A., Okin, G. S., Piketh, S., Saeed, T., Seibert, D., Shi, Z., Williams, E., Sellitto, P., and Formenti, P.: Mid- and Far-Infrared Spectral Signatures of Mineral Dust from Low- to High-Latitude Regions: significance and implications, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-3512, 2025.
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RC1: 'Comment on egusphere-2025-3512', Anonymous Referee #1, 04 Sep 2025
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This paper articulates and fills a clear gap in the literature: the scarcity of measurements of mineral dust optical properties beyond a wavelength of ~15 um. The paper is also well written and the methodology rigorous, following previous very well-regarded work by the main authors. I do have two important comments about the framing of the paper that should be addressed before publication.
Major comments:
- The authors take two samples of Icelandic dust to be representative of high-latitude dust. However, because Iceland is a volcanic island the mineralogical composition of its dust is likely to be quite different (more basaltic and darker) than that of other high-latitude sources, which are normally more silicate and quartz rich. The mineralogy of Icelandic dust might thus be an outlier among high-latitude dust sources and should not be taken as representative of high-latitude dust sources. I recommend that the authors replace “high latitude dust” with “Icelandic dust” in the title, abstract, and so forth. If the authors do want to take the Icelandic dust as representative then they should provide evidence that this is reasonable to do, for instance from a comparison of the mineralogy of Icelandic dust to that of other high-latitude sources.
- The authors state at various locations in the manuscript that the optical properties in the far infrared region (beyond 15 um) are important to climate and remote sensing. However, conventional wisdom is that (dust) absorption (well) outside of the atmospheric window does not matter much because the atmosphere is very opaque beyond 15 um due to abundant absorption by water vapor. So I have a hard time imagining that the dust interaction with radiation would normally matter much for Earth’s radiation budget. Two exceptions worth highlighting are for dust in the upper troposphere and for dust in the Arctic (mentioned in the paper), but the dust concentration is very low in both locations. A clearer argument could be made for remote sensing, as long as it’s made clear that this would only work in the upper troposphere / stratosphere and the dry poles. If the authors do want to make the point that dust interactions with radiation beyond 15 um matter for Earth’s climate, I recommend they show (1) Earth’s outgoing radiation as a function of wavelength and (2) the height in the atmosphere at which the optical depth to TOA equals 1 (the emission height) for one or more standard profiles (e.g., mid-latitude summer). That can make at least a qualitative argument that the dust optical properties for wavelengths larger than 15 um matter for Earth’s radiation budget.
Minor comments:
- Line 68: the 88% here seems very specific. My recollection of these papers also is that the error bar on the net DRE overlapped with zero, meaning that the dust-radiation interactions in the infrared could be >100% of those in the shortwave spectrum.
- Many citations that are part of the sentence are listed with parentheses, which is a bit tedious to read. For instance, line 263 should probably be “The Sadrian et al. (2023) dataset…” instead of “The (Sadrian et al., 2023) dataset…”
Citation: https://doi.org/10.5194/egusphere-2025-3512-RC1
Data sets
Absorbance spectra of Mineral Dust from Low- to High-Latitude Regions in the Mid- and Far-Infrared spectral range (2.5-25 µm) Claudia Di Biagio et al. https://doi.org/10.57932/905eff0b-d508-4aad-a422-5708e3132790
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Claudia Di Biagio
CORRESPONDING AUTHOR
Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
Elisa Bru
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Avila Orta
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Servanne Chevaillier
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Clarissa Baldo
Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Antonin Bergé
Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
now at: Laboratoire des Sciences du Climat et de l'Environnement, CEA–CNRS–UVSQ, IPSL, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
Mathieu Cazaunau
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Sandra Lafon
Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
Sophie Nowak
Université Paris Cité, CNRS, ITODYS, Paris F-75013, France
Edouard Pangui
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Meinrat O. Andreae
Max Planck Institute for Chemistry, 55128 Mainz, Germany
Department of Geology and Geophysics, King Saud University, Riyadh, Saudi Arabia
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
Pavla Dagsson-Waldhauserova
Faculty of Environmental and Forest Sciences, Agricultural University of Iceland, 311 Hvanneyri, Iceland
Faculty of Environmental Sciences, Department of Water Resources and Environmental Modeling, Czech University of Life Sciences Prague, 165 00 Prague, Czech Republic
Kebonyethata Dintwe
Department of Environmental Science, University of Botswana, Gaborone, Botswana
Konrad Kandler
Institute of Applied Geosciences, Technical University of Darmstadt, 64287 Darmstadt, Germany
James S. King
Université de Montréal, Québec, Canada
Amelie Chaput
Université de Montréal, Québec, Canada
now at: Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore
Gregory S. Okin
Department of Geography, University of California – Los Angeles, Los Angeles, California, USA
Stuart Piketh
NorthWest University, Potchefstroom, South Africa
Thuraya Saeed
Department of Physics, Lakehead University, Thunder Bay, Ontario, Canada
David Seibert
Walden University, Minneapolis, Minnesota, USA
Zongbo Shi
School of Geography, Earth and Environmental Science, University of Birmingham, Birmingham, B15 2TT, U.K.
Earle Williams
Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Pasquale Sellitto
Univ Paris Est Creteil and Université Paris Cité , CNRS, LISA, F-94010 Créteil, France
Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy
Paola Formenti
Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
Short summary
Spectroscopy measurements show that the absorbance of dust in the far-infrared up to 25 μm is comparable in intensity to that in the mid-infrared (3–15μm) suggesting its relevance for dust direct radiative effect. Data evidence different absorption signatures for high and low/mid latitude dust, due to differences in mineralogical composition. These differences could be used to characterise the mineralogy and differentiate the origin of airborne dust based on infrared remote sensing observations.
Spectroscopy measurements show that the absorbance of dust in the far-infrared up to 25 μm is...