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. The optical properties of airborne mineral dust depend on its mineralogy,size distribution, and shape, and they might vary between different sourceregions. To date, large differences in refractive index values found in theliterature have not been fully explained. In this paper we present a newdataset of complex refractive indices (    m  =  n  -  i  k) and single-scattering albedos(SSAs) for 19 mineral dust aerosols over the 370–950 nm range in dryconditions. Dust aerosols were generated from natural parent soils fromeight source regions (northern Africa, Sahel, Middle East, eastern Asia,North and South America, southern Africa, and Australia). They were selectedto represent the global-scale variability of the dust mineralogy. Dust wasresuspended into a 4.2 m 3  smog chamber where its spectral shortwavescattering ( βsca ) and absorption ( βabs )coefficients, number size distribution, and bulk composition were measured.The complex refractive index was estimated by Mie calculations combiningoptical and size data, while the spectral SSA was directly retrieved from βsca  and  βabs  measurements. Dust is assumed to bespherical in the whole data treatment, which introduces a potential sourceof uncertainty. Our results show that the imaginary part of the refractiveindex ( k ) and the SSA vary widely from sample to sample, with values for  k  inthe range 0.0011 to 0.0088 at 370 nm, 0.0006 to 0.0048 at 520 nm, and 0.0003to 0.0021 at 950 nm, as well as values for SSA in the range 0.70 to 0.96 at 370 nm,0.85 to 0.98 at 520 nm, and 0.95 to 0.99 at 950 nm. In contrast, the realpart of the refractive index ( n ) is mostly source (and wavelength)independent, with an average value between 1.48 and 1.55. Thesample-to-sample variability in our dataset of  k  and SSA is mostly related todifferences in the dust iron content. In particular, awavelength-dependent linear relationship is found between the magnitude of k  and SSA and the mass concentrations of both iron oxide and total elementaliron, with iron  oxide better correlated than total elemental iron with both k  and SSA. The value of  k  was found to be independent of size. When the ironoxide content exceeds 3 %, the SSA linearly decreases with an increasingfraction of coarse particles at short wavelengths (   Compared to the literature, our values for the real part of the refractiveindex and SSA are in line with past results, while we found lower values of k  compared to most of the literature values currently used in climate models.   We recommend that source-dependent values of the SW spectral refractiveindex and SSA be used in models and remote sensing retrievals instead ofgeneric values. In particular, the close relationships found between  k  or SSAand the iron content in dust enable the establishment of predictive rules forspectrally resolved SW absorption based on particle composition.

Complex refractive indices and single-scattering albedo of global dust aerosols in the shortwave spectrum and relationship to size and iron content