Physical, chemical and optical properties of Australian desert dust: a multiple analysis from several sites.

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.Leibniz Institute for Tropospheric Research; Georgia Institute of Technolog