Absorbance spectra of Mineral Dust from Low- to High-Latitude Regions in the Mid- and Far-Infrared spectral range (2.5-25 µm)

Laboratory measurements of the absorbance spectra for thirteen mineral dust aerosol samples of different origin. Data are reported as absorbance versus wavelength. The name of each dataset indicate the origin of the dust sample.
Absorbance spectra were acquired based on a pellet spectroscopy technique that consists in dispersing the aerosol particles in a matrix of transparent material which is then pressed to form a homogeneous pellet. The transmission spectrum of the pellet was measured to obtain the absorbance of the aerosol sample. To apply this technique aerosol samples were re-suspended in the laboratory from natural soil samples using the same protocol previously described by Di Biagio et al. (2017) (https://doi.org/10.5194/acp-17-1901-2017) and Baldo et al. (2023) (https://doi.org/10.5194/egusphere-2023-276).
The collected dust aerosols were used to produce pellets. Pellet samples were realized using Potassium Bromide (KBr for IR spectroscopy Uvasol®, CAS No 7758-02-3, lot. B1978207 142) as transparent matrix in which the dust grains collected from soil resuspension were dispersed. A quantity of 0.5 mg of dust was weighed and diluted in 300 mg of KBr (corresponding to 0.16% of dust in KBr). Additionally, six pure 300 mg KBr pellets were produced. All the pellets were kept in the oven at 110 °C until they were used for spectroscopy measurements in order to minimize water vapour absorption on their surface.
Absorbance spectra were recorded between 2.5 and 25 µm (4000-400 cm-1 wavenumber) at 0.5 cm 1 resolution by means of a PerkinElmer Spectrum Two FT-IR spectrometer. The instrument uses a Globar source, with a KBr beamsplitter and a deuterated triglycine sulphate (DTGS) detector. Pellets were placed in the spectrometer chamber. A background spectrum was acquired prior each pellet measurement and subtracted to remove the signatures of CO2 and H2O possibly present in the cell. A total of 10 scans were averaged to produce the dust-KBr and the pure KBr spectra, respectively. Each dust-KBr spectrum was corrected by subtracting the pure KBr spectrum that best fit the baseline of each dust-KBr pellet. The uncertainty in the measured absorbance is less than 5% and has been estimated as the 3σ variability of the signal in the regions of no dust absorption (A< 0.01).
Thirteen dust samples were investigated in this study from different source areas worldwide. Samples from low and mid latitude areas originated from: Morocco, Niger, Bodélé (Chad), Saudi Arabia, Kuwait, Gobi (China), Arizona, Atacama (Chile), Namibia (two samples named Namib-1 and Namib-H), and Botswana. Samples from high latitude areas originated from Iceland (two samples named Iceland-M and Iceland-H).