Articles | Volume 16, issue 17
Atmos. Chem. Phys., 16, 10809–10830, 2016
Atmos. Chem. Phys., 16, 10809–10830, 2016

Technical note 31 Aug 2016

Technical note | 31 Aug 2016

Technical note: Mineralogical, chemical, morphological, and optical interrelationships of mineral dust re-suspensions

Johann P. Engelbrecht1, Hans Moosmüller1, Samuel Pincock1, R. K. M. Jayanty2, Traci Lersch3, and Gary Casuccio3 Johann P. Engelbrecht et al.
  • 1Desert Research Institute (DRI), Reno, Nevada 89512-1095, USA
  • 2RTI International, Raleigh, North Carolina 27675-9000, USA
  • 3RJ Lee Group, Inc., Monroeville, Pennsylvania 15146, USA

Abstract. This paper promotes an understanding of the mineralogical, chemical, and physical interrelationships of re-suspended mineral dusts collected as grab samples from global dust sources. Surface soils were collected from arid regions, including the southwestern USA, Mali, Chad, Morocco, Canary Islands, Cabo Verde, Djibouti, Afghanistan, Iraq, Kuwait, Qatar, UAE, Serbia, China, Namibia, Botswana, Australia, and Chile. The  <  38 µm sieved fraction of each sample was re-suspended in a chamber, from which the airborne mineral dust could be extracted, sampled, and analyzed. Instruments integrated into the entrainment facility included two PM10 and two PM2.5 filter samplers, a beta attenuation gauge for the continuous measurement of PM10 and PM2.5 particulate mass fractions, an aerodynamic particle size analyzer, and a three-wavelength (405, 532, 781 nm) photoacoustic instrument with integrating reciprocal nephelometer for monitoring absorption and scattering coefficients during the dust re-suspension process. Filter sampling media included Teflon® membrane and quartz fiber filters for chemical analysis 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  >  75,  <  125 µm soil fractions were mineralogically assessed by optical microscopy. Presented here are results of the optical measurements, showing the interdependency of single-scattering albedos (SSA) at three different wavelengths and mineralogical content of the entrained dust samples. To explain the elevated concentrations of iron (Fe) and Fe ∕ Al ratios in the soil re-suspensions, we propose that dust particles are to a large extent composed of nano-sized particles of micas, clays, metal oxides, and ions of potassium (K+), calcium (Ca2+), and sodium (Na+) evenly dispersed as a colloid or adsorbed in amorphous clay-like material. Also shown are differences in SSA of the kaolinite/hematite/goethite samples from Mali and those from colloidal soils elsewhere. Results from this study can be integrated into a database of mineral dust properties, for applications in climate modeling, remote sensing, visibility, health (medical geology), ocean fertilization, and impact on equipment.

Short summary
This laboratory study was performed on re-suspended dust samples collected from several known dust sources of the world. We measured dust by multiple analytical techniques to understand their physical and chemical characteristics. Studies of the properties of dust are necessary to assess the magnitude of the growing dust problem, identify sources of dust, and, where feasible, apply preventative measures and remediation practices. Results can be used in global climate and health studies.
Final-revised paper