Characteristics of airborne ultrafine and coarse particles during the Australian dust storm of 23 September 2009

Particle number concentrations and size distributions, visibility and particulate mass concentrations and weather parameters were monitored in Brisbane, Australia, on 23 September 2009, during the passage of a dust storm that originated 1400 km away in the dry continental interior. The dust concentration peaked at about mid-day when the hourly average PM(2.5) and PM(10) values reached 814 and 6460 mu g m(-3), respectively, with a sharp drop in atmospheric visibility. A linear regression analysis showed a good correlation between the coefficient of light scattering by particles (Bsp) and both PM(10) and PM(2.5). The particle number in the size range 0.5-20 mu m exhibited a lognormal size distribution with modal and geometrical mean diameters of 1.6 and 1.9 mu m, respectively. The modal mass was around 10 mu m with less than 10% of the mass carried by particles smaller than 2.5 mu m. The PM(10) fraction accounted for about 68% of the total mass. By mid-day, as the dust began to increase sharply, the ultrafine particle number concentration fell from about 6 x 10(3) cm(-3) to 3 x 10(3) cm(-3) and then continued to decrease to less than 1 x 10(3) cm(-3) by 14 h, showing a power-law decrease with Bsp with an R(2) value of 0.77 (p < 0.01). Ultrafine particle size distributions also showed a significant decrease in number during the dust storm. This is the first scientific study of particle size distributions in an Australian dust storm. (C) 2011 Elsevier Ltd. All rights reserved.