AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
3-D Reconstruction of Individual Ambient Dust Particles to Study Variation in Aerosol Optical Properties
DIANA ORTIZ-MONTALVO, Joseph Conny, Robert Willis, National Institute of Standards and Technology
Abstract Number: 361 Working Group: Single Aerosol Particle Studies - Techniques and Instrumentation
Abstract Ambient particles are ubiquitous in the atmosphere and exert a strong influence on the climate by altering the Earth's radiative balance. Their optical properties depend highly on the shape and how the chemical compounds are arranged in its internal structure. The objective of this study is to characterize the morphology and composition of ambient dust particles and study their optical properties using a method that combines advanced microscopy techniques and optical property modeling. Focused ion-beam scanning electron microscopy and energy-dispersive x-ray spectroscopy (FIB-SEM-EDS) was successfully used to reconstruct the three-dimensional (3-D) configuration of particles. 3-D reconstruction included the particle's inherent shape, voids and inclusions whether the inclusions were light-absorbing or light-scattering phases. The 3-D reconstructions were then used in a discrete dipole approximation method (DDA) to determine their optical properties such as single-scattering albedo (SSA) and fraction of backscattered light. Optical properties where obtained using actual-shapes of the particles, as well as, (theoretical) equivalently-sized shapes that would scatter light isotopically: spheres, cubes, and tetrahedral. This presented an interesting opportunity to test the commonly used assumption in climate models that particles are spherical. Results from a limited number of samples indicate that the shape of the particle was the dominant factor affecting the variation of optical properties. Also, SSA for the tetrahedral geometric model was much closer to the albedo of reference particles. These findings perhaps suggest that the use of tetrahedral geometric models would be a better way of representing atmospheric dust in modeling studies, rather than commonly used spherical models. Lastly, the effect that size has on the optical properties of these 3-D reconstructions is currently being explored.
Overall, the use of 3-D reconstructions of individual particles offers a more realistic way of reproducing irregularly shaped ambient particles to study their optical properties with models such as DDA.