Comparison of Different Approaches for Measurement of Surface Area of Nanoaerosols

BON KI KU, Pramod Kulkarni

Centers for Desease Control and Prevention, National Institute for Occupational Safety and Health

     Abstract Number: 280
     Last modified: May 3, 2010

Abstract
Recent studies have indicated that the toxicity of low-solubility nanoparticles may be more appropriately associated with particle surface area than mass (Heitbrink et al., 2009), suggesting that surface area as a dose metric may be more appropriate for exposure studies. There are a range of instruments and techniques available for measurement of aerosol surface area, each with its own advantages and limitations. Portable and semi-empirical instruments, that are most attractive for field measurements, also tend to be limited in terms of reliability of their measurements while reliable laboratory instruments and methods are not conducive to field measurements. Diffusion charging-based semi-empirical instruments are being increasingly used for field exposure studies; however these instruments have not been adequately characterized in terms of their measurement accuracy and precision. In this study, four different approaches for measuring surface area were compared in the submicrometer size range: (i) three diffusion charging-based sensors (nanoparticle surface area monitor, TSI Inc., model 3550; diffusion charger, Ecochem, model DC2000CE; diffusion charger, Matter Engineering, model LQ1-DC), (ii) mobility diameter based approach, (iii) surface area based on mobility diameter of a chain aggregate with uniform particle size, and finally, (iv) tandem mobility-mass approach. It was found that the response of the three diffusion charging-based sensors to silver agglomerates were similar but substantially underestimated the true geometric surface area by a factor of 3 - 10 in the size range studied. These differences in true geometric area and that measured by diffusion charging based instruments could be even more drastic for complex aerosols with high dynamic shape factors, such as carbon nanotube agglomerates. The results show that caution should be exercised in the interpretation of measurements from diffusion charging-based semi-empirical instruments.