Mineral Dust Aerosol

Derbyshire E. Aerosolic mineral dust and human health. In Medical Geology—Earth Science in Support of Public... 

Dry aerosols, or particulate matter, differ so much from the carrying gas stream that their removal should present no major difficulties. The aerosol is different physically, chemically, and electrically. It has vastly different inertial properties than the carrying gas stream and can be subjected to an electric charge. It may be soluble in a specific liquid. With such a variety of removal mechanisms that can be applied, it is not surprising that particulate matter, such as mineral dust, can be removed by a filter, wet scrubber, or electrostatic precipitator with equally satisfactory results. 

Li, X., H. Mating, D. Savoie, K. Voss, and J. M. Prospero, "Dominance of Mineral Dust in Aerosol Light-Scattering in the North Atlantic Trade Winds, Nature, 380, 416-419 (1996). 

Li-Jones, X., H. B. Mating, and J. M. Prospero, Effect of Relative Humidity on Light Scattering by Mineral Dust Aerosol As Measured in the Marine Boundary Layer over the Tropical Atlantic Ocean, J. Geophys. Res., 103, 31113-31121 (1998). 

Tegen, I., and A. A. Lacis, Modeling of Particle Size Distribution and Its Influence on the Radiative Properties of Mineral Dust Aerosol, J. Geophys. Res., 101, 19237-19244 (1996). 

The chemical composition of PM10 shows a considerable conformity in these countries. Always, secondary inorganic aerosols (SIA) are the major constituent ( 40%) followed by the carbonaceous compounds ( 25%). Contributions of sea salt and mineral dust vary between 10% and 15% depending on presence and distance of respective sources. The unidentified mass is some 15% indicating that the composition of PM10 in this region is fairly well known. 

Atmospheric particles in the troposphere are composed of a complex mixture of highly water-soluble inorganic salts, insoluble mineral dust, and carbonaceous material (which includes organic compounds plus elemental carbon) (Jacobson et al., 2000). Studies in which the chemical composition has been determined as a function of particle size demonstrate a correlation between the chemical composition and the size mode of atmospheric aerosols (Meszaros et al., 1997 Krivacsy and Molnar, 1998 Alves et al.,2000 Maenhaut et al.,2002 Smolik et al., 2003 Samara andVoutsa, 2005). 

GCM (Global) aimnomum, prescribed for mineral dust aerosol number not with prescribed properties based... 

BC, OC, sea-salt, dust, water, Ca " sea-salt Sectional (6) prescribed for mineral dust Modal (1) prescribed size distribution for other aerosols single size distribution for all aerosols externally mixed with internally-mixed S04 , sea-salt, and H2O different aerosol mixing states for chemistry and radiative forcing calculation included hygroscopicities on Mie theory with size- and wavelength- dependent refractive indices... 

The first application is the simulation of a mineral dust event over West Africa in March 2004. During this event there were high wind speeds and low temperature observed in the Sahara and heavy precipitations over Libya (Knipperts and Fink 2006). Figure 6.2 shows the simulated dust loading for 4th March 2004 at 12 UTC. To investigate the impact of the dust aerosols on radiation two simulations were performed one with no interaction between the actual aerosol concentration and radiation, and another that takes into account the interaction. 

A number of studies have speculated on diazotroph response to mineral dust Fe fertilization in the Atlantic (Mahaffey et al, 2003), and Pacific Oceans (Johnson et al, 2003). Circumstantial evidence for dust stimulation of marine diazotrophic biomass has recently been reported. A 1999 Saharan dust event coincided with increases in dissolved Fe concentrations on the west Florida shelf and a 100-fold increase in Trichodesmium biomass. N2 fixation rates were not measured, but DON concentrations doubled, presumably due to exudation by N2 fixers (Lenes et al, 2001). A recent Saharan dust addition experiment to surface water samples collected along a west African cruise transect (35°W-17°W), found a minimal increase in CO2 fixation and a large stimulation in N2 fixation, suggesting that diazotrophs were co-limited by both P and Fe (Mills et al, 2004). Note however, analysis of aerosol dust shows that while providing Fe, it also supplies P and combined N (Baker et al, 2003 Mills et al, 2004 Ridame and Guieu, 2002). 

A newly developed aerosol mass spectrometer (Jayne et ah, 2000 Allan et ai, 2003) deposits size-selected particles on a heated surface so that volatile and semi-volatile materials are vaporized. These are then analyzed quantitatively on line. The instrument is able to provide quantitative, short-time-resolution measurements of the compositions of particles in selected size ranges. However, the instrument has poor sensitivity for refractory materials such as mineral dust and provides no information on particle-to-particle variability in composition. 

Li X., Mating H., Savoie D., Voss K., and Prospero J. M. (1996) Dominance of mineral dust in aerosol light-scattering in the North Atlantic trade winds. Nature 380, 416-419. 

Reader M. C., Fung I., and McFarlane N. (1999) The mineral dust aerosol cycle during the Last Glacial Maximum. J. Geophys. Res. 104, 9381-9398. 

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