Investigations of the March 2006 African dust storm using ground‐based column‐integrated high spectral resolution infrared (8–13 μm) and visible aerosol optical thickness measurements: 2. Mineral aerosol mixture analyses

Abstract

The mineral aerosol mixture composition for the March 2006 Saharan dust storm is assessed in this paper on the basis of the analysis of visible to near‐infrared (VIS‐NIR) and infrared (IR) aerosol optical thickness (AOT) spectra obtained during the Portable Infrared Aerosol Transmission Experiment (PIRATE). The AOT spectra from 8 to 13 μm were determined using column‐integrated solar transmission measurements using a Fourier transform infrared spectrometer. To determine the mineralogy and mixture composition of the dust, we determined the expected mineralogy of dust from the Algerian source region in a dust storm environment. Then we computed the modeled VIS‐IR AOT spectra using Mie theory for external and internal mixtures. We compared the modeled VIS‐NIR AOT spectra and derived index of refraction and single‐scattering albedo with the measured values from AERONET and compared the modeled IR AOT spectra with the values from our IR measurements. The fit between the measured and modeled values was best when we used an extinction resonance correction to the Mie theory results to better account for the exact wavelengths and shapes of some of the AOT peaks for mineral particles. The mineralogy and mixture composition of the best dust model includes external mixtures, internal mixtures, and mineralogy dominated by quartz, illite, and calcite. The modeled mean radius was determined, and several modes were computed in agreement with AERONET results.