Using a laser aureole to study aerosols

Aerosol optical scattering experiments are often large, expensive, and provide poor control of dust uniformity and size distribution. The size distribution of such suspended atmospheric aerosols varies rapidly in time, since larger particles settle quickly. Even in large chambers, 10 micron particles settle in tens of seconds. We describe lab-scale experiments with stable particle distributions. A viscous colloidal solution can stabilize the particles for sufficient time to measure optical scattering properties. Colloids with different concentrations or size distributions enable nearly time independent studies of prepared distributions. We perform laser aureole scattering from a colloid containing a few percent by volume of Arizona Road Dust (ARD) in mineral oil and glycerin, and 1-micron polystyrene spheres in water. We discuss aureole analysis, the differences expected in scattering properties due to the index of refraction of the mineral oil medium versus air, and the impact of non-spherical shape on the scattering. This research demonstrates that particles suspended in a viscous medium can be used to simulate aerosol optical scattering in air, while enabling signal averaging, offering reproducibility, and easing problems resulting from parameter variations in studies of dust properties.

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