AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Estimation of Electron Microscopy Image-based Aerodynamic and Diffusion Diameters for Carbon Nanotube Aerosols
BON KI KU, Pramod Kulkarni, Centers for Disease Control and Prevention, NIOSH
Abstract Number: 442 Working Group: Health Related Aerosols
Abstract Knowing transport characteristics of aerosol particles is important in assessing their fate in the respiratory system. Diffusion and aerodynamic diameters typically capture key deposition mechanisms in the submicrometer size range. However, for nonspherical particles with high aspect ratios, such as aerosolized carbon nanotubes, these diameters can vary widely, requiring their independent measurement. The objective of this study was to estimate aerodynamic and diffusion-equivalent diameters of airborne carbon nanotubes (CNTs) and compare these estimates with those directly measured using real-time instruments. The as-received nanomaterials were aerosolized using different techniques including dry dispersion and nebulization. The airborne properties of the particles were measured using real-time instruments by tandem mobility-mass approach. Particles with single electrical mobility were collected on a grid and analyzed by Transmission Electron Microscopy (TEM) to obtain an aerodynamic diameter of the particles. From the TEM image analysis, projected area, maximum length, and 2-D radius of gyration were measured. An approach was developed to estimate the aerodynamic diameter by estimating radius of gyration and projected area equivalent diameter from the particle image, and the material density known from the manufacturer. Without accounting for particle shape correction, the aerodynamic diameters calculated from microscopy were overestimated compared to direct measurements. After accounting for the dynamic shape factor correction, most of the estimated data agree with the direct measurements within 30%. The uncertainty of these estimates depends on degree of overlapping features in the particle structure, and nonuniformity in tube diameter and material density. The approach could be useful in calculating approximate airborne properties from microscopy images of carbon nanotube agglomerates with relatively open structures, when other methods are not readily available.