| The pace of nanomaterial manufacturing is accelerating, exposing increasing numbers of workers to potentially adverse health effects. At sites where nanomaterials are synthesized or used, they may enter workers' breathing zones. Toxicity studies suggest that, of all the categories of nanomaterials, carbon nanotubes are of particular concern.Effective exposure assessment methods for airborne nanomaterials are lacking. This shortfall is related to their ability to confound detection because of their unusual properties. Such properties include small mass despite large number concentration, large surface area, and for nanotubes, large aspect ratio.Air monitoring instruments such as differential mobility analyzers are aerosol-based detection methods. These are not necessarily the preferred method for studying nanoparticles in air. Many such instruments can detect the presence of aerosols but not identify their composition. On the other hand, the composition of some aerosol particles can be identified using Raman spectroscopy and other techniques. Nonetheless, air-monitoring instruments have their merits, are widely used, and were the main detection method considered in this dissertation. Understanding how these instruments interact with aerosols containing nanotubes requires the ability to routinely generate a test aerosol. However, carbon nanotubes are difficult to aerosolize. To this end, an electrospray system was developed (Chapter 2), making possible the reproducible generation of occupationally relevant mass concentrations of nanotubes in carrier gas.Using this electrospray system, five kinds of nanotube aerosols were produced and their morphologies studied (Chapter 3) using electron microscopy. One of these morphologies, a super nanostructure called "the coil", was detected and has not been observed before as an aerosol particle to our knowledge. Electron microscopy also revealed residual metal particles so deeply embedded within the nanotube structure, their removal would be impossible, despite rigorous post-processing.Air monitoring instruments were challenged with nanotube aerosols, and their responses evaluated (Chapter 4). These studies revealed that the P-Trak, P-CPC, and DustTrak under-report number and mass concentration. Likewise, some electric mobility-based instruments are unable to accurately measure particle size distribution. Specifically, the SMPS configuration UCPC/NDMA is unusable with nanotube aerosols, and if an electric mobility-based instrument must be used, the CPC/LDMA is recommended. |
