Generation of submicron Arizona test dust aerosol:: Chemical and hygroscopic properties

This article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas-aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30-1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Sub-micron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100-200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.