Mineralogical, Chemical, and Optical Interrelationships of Airborne Mineral Dusts

Abstract:

The purpose of the project was to provide information on the mineralogical, chemical and physical interrelationships of re-suspended mineral dust samples collected as grab samples from global dust sources. Surface soil samples were collected from about 65 desert sites, including the southwestern USA (12), Mali (3), Chad (3), Morocco (1), Canary Islands (8), Cape Verde (1), Djibouti (1), Afghanistan (3), Iraq (6), Kuwait (5), Qatar (1), UAE (1), Serbia (3), China (5), Namibia (3), Botswana (4), Australia (3), and Chile (1).

The < 38 µm sieved fraction of each sample was re-suspended in an entrainment chamber, from which the airborne mineral dust could be monitored, sampled and analyzed. Instruments integrated into the entrainment facility included two PM₁₀ and two PM_2.5 filter samplers, a beta attenuation gauge for the continuous measurement of PM₁₀ and PM_2.5 particulate mass fractions, an aerodynamic particle size (APS) analyzer, and a three wavelength (405, 532, 781nm) photoacoustic resonator with integrating reciprocal nephelometer for monitoring absorption and scattering coefficients during the dust re-suspension process. Filter sample media included Teflon® membrane and quartz fiber filters for chemical analysis (71 species), and Nuclepore® filters for individual particle analysis by Scanning Electron Microscopy (SEM). The < 38 µm sieved fractions were also analyzed by X-ray diffraction for their mineral content while the > 38 µm, < 125 µm soil fractions were mineralogically characterized by optical microscopy.

We will be presenting results on the optical measurements, also showing the relationship between single scattering albedo (SSA) at three different wavelengths, and chemical as well as mineralogical content and interdependencies of the entrained dust samples. Examples showing the relationships between the single scattering albedos of airborne dusts, and iron (Fe) in hematite, goethite, and clay minerals (montmorillonite, illite, palygorskite), will be discussed. Differences between the clay minerals in samples from Mali and those from other localities are demonstrated.

We intend establishing a data base for applications in climate modeling, remote sensing, visibility, health (medical geology), ocean fertilization, and damage to equipment.