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Original Research Papers

Spectral absorption coefficients and imaginary parts of refractive indices of Saharan dust during SAMUM-1

Authors:

T. Müller ,

Leibniz Institute for Tropospheric Research, DE
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A. Schladitz,

Leibniz Institute for Tropospheric Research, DE
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A. Massling,

Leibniz Institute for Tropospheric Research, DE
About A.
Now at: National Environmental Research Institute, Aarhus University, 4000 Roskilde, Denmark
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N. Kaaden,

Leibniz Institute for Tropospheric Research, DE
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K. Kandler,

Applied Geosciences Department, Darmstadt University of Technology, DE
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A. Wiedensohler

Leibniz Institute for Tropospheric Research, DE
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Abstract

During the SAMUM-1 experiment, absorption coefficients and imaginary parts of refractive indices of mineral dust particles were investigated in southern Morocco. Main absorbing constituents of airborne samples were identified to be iron oxide and soot. Spectral absorption coefficients were measured using a spectral optical absorption photometer (SOAP) in the wavelength range from 300 to 800 nm with a resolution of 50 nm. A new method that accounts for a loading-dependent correction of fibre filter based absorption photometers, was developed. The imaginary part of the refractive index was determined using Mie calculations from 350 to 800 nm. The spectral absorption coefficient allowed a separation between dust and soot absorption. A correlation analysis showed that the dust absorption coefficient is correlated (R2 up to 0.55) with the particle number concentration for particle diameters larger than 0.5 μm, whereas the coefficient of determination R 2 for smaller particles is below 0.1. Refractive indices were derived for both the total aerosol and a dust aerosol that was corrected for soot absorption. Average imaginary parts of refractive indices of the entire aerosol are 7.4 × 10−3, 3.4 × 10−3 and 2.0 × 10−3 at wavelengths of 450, 550 and 650 nm. After a correction for the soot absorption, imaginary parts of refractive indices are 5.1 × 103, 1.6 × 103 and 4.5 × 104.

How to Cite: Müller, T., Schladitz, A., Massling, A., Kaaden, N., Kandler, K. and Wiedensohler, A., 2009. Spectral absorption coefficients and imaginary parts of refractive indices of Saharan dust during SAMUM-1. Tellus B: Chemical and Physical Meteorology, 61(1), pp.79–95. DOI: http://doi.org/10.1111/j.1600-0889.2008.00399.x
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  Published on 01 Jan 2009
 Accepted on 22 Sep 2008            Submitted on 12 Mar 2008

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