Browsing by Author "Mitchell, RM"

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    Optical, physical and chemical characteristics of Australian desert dust aerosols: results from a field experiment
    (European Geosciences Union, 2009-11-25) Radhi, M; Box, A; Box, GP; Mitchell, RM; Cohen, DD; Stelcer, E; Keywood, MD
    Mineral dust is one of the major components of the world's aerosol mix, having a number of impacts within the Earth system. However, the climate forcing impact of mineral dust is currently poorly constrained, with even its sign uncertain. As Australian deserts are more reddish than those in the northern hemisphere, it is important to better understand the physical, chemical and optical properties of this important aerosol. We have investigated the properties of Australian desert dust at a site in SW Queensland, which is strongly influenced by both dust and biomass burning aerosol. Three years of ground-based monitoring of spectral optical thickness has provided a statistical picture of gross aerosol properties. In November 2006 we undertook a field campaign which collected 4 sets of size-resolved aerosol samples for laboratory analysis – both ion beam analysis and ion chromatography. © 2009, European Geosciences Union
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    Physical and chemical properties of Australian desert dust, Aeolian dust: its potential role as a carrier of terrestrial salt in Australia
    (Australian Nuclear Science and Technology Organisation, 2008-07) Radhi, M; Box, MA; Box, GP; Mitchell, RM; Keywood, D; French, D; Cohen, DD; Stelcer, E
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    Physical, chemical and optical properties of Australian desert dust: a multiple analysis from several sites
    (3rd International Workshop on Mineral Dust, 2008-09) Radhi, M; Box, MA; Box, GP; Mitchell, RM; Keywood, MD; French, D; Cohen, DD; Stelcer, E
    Australian dust aerosol was sampled at two desert locations, Birdsville (25.54 S, 139.20 E) and Muloorina (29.14 S, 137.64 E), using a 12-stage MOUDI sampler. Backgound TSP levels were 15.8 ± 3 μg/m3 at Birdsville, and 244 ± 10 μg/m3 at Muloorina. Ion beam analysis shows that the following elements are dominant at both sites: Na, Al, Si, Cl, K, Ca, Ti and Fe. Sulphur is the only pollutant element that occurred in the Muloorina analysis due to local vegetation burning. Weather conditions during sampling at Birdsville were classified as non-dusty to weak dust. At Muloorina we had different weather conditions: non-dust, weak dust and dust storm. The concentrations of the element loading in the atmosphere varied with weather conditions. The mass ratio of the other elements to Al also varied with the weather conditions. For both sites Fe occurred in fine and coarse size ranges, appearing strongly in the size range 1.8 to 10 μm in all events. The Fe/Al mass ratio was 1.97, 2.5, 0.96 and 1.02 for non dust, weak dust and north and south dust storm respectively at Muloorina, while at Birdsville the value was in the range 0.45 to 0.65, indicating Muloorina is rich in Fe. Both Na and Cl demonstrated a good correlation with Al as Australian desert dust also contains a mixture of salts from dry saline lakes. Selected filters are currently undergoing electron microscopy analysis in order to determine the mineralogical content, especially hematite vs. goethite. The monthly mean of the aerosol optical depth at Birdsville shows maximum values during summer (Feb. 0.06 ± 0.05) and spring (Oct. 0.11 ± 0.05), and minimum values in June (0.02 ± 0.001). The Ångström exponent was low (suggesting coarse particles) during summer and spring. The relationship between AOD and Ångström exponent shows a good pattern of decreasing α with increasing AOD, indicating the effects of dust particles.
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    Size-resolved mass and chemical properties of dust aerosols from Australia's Lake Eyre Basin
    (Elsevier, 2010-09) Radhi, M; Box, MA; Box, GP; Mitchell, RM; Cohen, DD; Stelcer, E; Keywood, MD
    Australia is the dominant mineral dust source in the southern hemisphere, yet the physical, chemical and optical properties of Australian dust aerosol are presently poorly understood. We have investigated the properties of Australian aerosol at a site near Lake Eyre in central Australia, which is strongly influenced by mineral dust. During a field campaign in November 2007 we collected eight sets of size-resolved aerosol samples for laboratory analysis: six during quiescent conditions, and two during dust storms. Ion Beam Analysis was used to determine the elemental composition of all filter samples. Scatter plots showed that Fe, Al and Ti were well correlated with Si, and hence soil-derived. The Fe/Si ratio was consistently higher than the global crustal average, confirming that Australian dusts are comparatively rich in Fe. Scatter plots for Na and Cl against Si showed clear evidence of a second aerosol population, associated with maritime advection. Profiles of water soluble ions for two sample sets, showed the importance of marine influences on both the fine and coarse modes, as well as the presence of organic acids. Estimates of the mass fraction of NaCl in our samples suggest that, for quiescent days, roughly 0.5% of the sample mass was NaCl. © 2010, Elsevier Ltd.