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Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum

Baldo, Clarissa; Formenti, Paola; Di Biagio, Claudia; Lu, Gongda; Song, Congbo; Cazaunau, Mathieu; Pangui, Edouard; ... Shi, Zongbo; + view all (2023) Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum. Atmospheric Chemistry and Physics , 23 (14) pp. 7975-8000. 10.5194/acp-23-7975-2023. Green open access

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Abstract

Icelandic dust can impact the radiative budget in high-latitude regions directly by affecting light absorption and scattering and indirectly by changing the surface albedo after dust deposition. This tends to produce a positive radiative forcing. However, the limited knowledge of the spectral optical properties of Icelandic dust prevents an accurate assessment of these radiative effects. Here, the spectral single scattering albedo (SSA) and the complex refractive index (mCombining double low linen-ik) of Icelandic dust from five major emission hotspots were retrieved between 370-950 nm using online measurements of size distribution and spectral absorption (βabs) and scattering (βsca) coefficients of particles suspended in a large-scale atmospheric simulation chamber. The SSA(λ) estimated from the measured βabs and βsca increased from 0.90-0.94 at 370nm to 0.94-0.96 at 950nm in Icelandic dust from the different hotspots, which falls within the range of mineral dust from northern Africa and eastern Asia. The spectral complex refractive index was retrieved by minimizing the differences between the measured βabs and βsca and those computed using the Mie theory for spherical and internally homogeneous particles, using the size distribution data as input. The real part of the complex refractive index (n(λ)) was found to be 1.60-1.61 in the different samples and be independent of wavelength. The imaginary part (k(λ)) was almost constant with wavelength and was found to be around 0.004 at 370nm and 0.002-0.003 at 950nm. The estimated complex refractive index was close to the initial estimates based on the mineralogical composition, also suggesting that the high magnetite content observed in Icelandic dust may contribute to its high absorption capacity in the shortwave part of the spectrum. The k(λ) values retrieved for Icelandic dust are at the upper end of the reported range for low-latitude dust (e.g., from the Sahel). Furthermore, Icelandic dust tends to be more absorbing towards the near-infrared. In Icelandic dust, k(λ) between 660-950nm was 2-8 times higher than most of the dust samples sourced in northern Africa and eastern Asia. This suggests that Icelandic dust may have a stronger positive direct radiative forcing on climate that has not been accounted for in climate predictions.

Type: Article
Title: Complex refractive index and single scattering albedo of Icelandic dust in the shortwave part of the spectrum
Open access status: An open access version is available from UCL Discovery
DOI: 10.5194/acp-23-7975-2023
Publisher version: https://doi.org/10.5194/acp-23-7975-2023
Language: English
Additional information: © Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License.
Keywords: Science & Technology, Life Sciences & Biomedicine, Physical Sciences, Environmental Sciences, Meteorology & Atmospheric Sciences, Environmental Sciences & Ecology, HIGH-LATITUDE DUST, VOLCANIC ASH AEROSOL, IN-SITU MEASUREMENTS, MINERAL-DUST, RADIATIVE PROPERTIES, SIZE DISTRIBUTION, MULTIPLE-SCATTERING, OPTICAL-PROPERTIES, BODELE DEPRESSION, IRON
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL SLASH
UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS
UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS > Dept of Geography
URI: https://discovery.ucl.ac.uk/id/eprint/10177505
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