Occupational exposure assessment for nanoparticles.

University of Minnesota Ph.D. dissertation. August 2009. Major: Environmental Health. Advisor: Gurumurthy Ramachandran. 1 computer file (PDF); xi, 165 pages.This dissertation consists of four sections which address various aspects of assessing exposure to nanoparticles and monitoring methods. The first section examines the appropriateness of different exposure metrics using multiple-metric measurements that were carried out in multiple locations of workplaces generating incidental nanoparticles to construct aerosol maps. The concentration peaks of SA and fine particle number agreed more with locations of nanoparticle sources and showed larger concentration ratios between work areas than mass concentration. This indicates that SA and fine particle number concentrations are more appropriate for nanoparticle than mass. The second section examines the ability of various exposure metrics to distinguish between exposure categories. Multiple-metric measurements were obtained in high and low exposure zones in workplaces generating incidental nanoparticles. SA and fine particle concentrations showed higher `contrast' in mean concentrations and larger concentration ratios between zones than mass concentrations. The results suggest that SA and fine particle number concentrations are more efficient than mass for classifying worker exposures into categories. The results suggest that the choice of appropriate exposure metrics is critical for classifying workers into similarly exposed groups. In the third section, SA concentrations were estimated in two ways based on number and/or mass concentrations using aerosol instruments and compared with SA directly measured using a diffusion charger. Estimated SA was derived from particle size distribution by number and was calculated using a simple inversion method. Both estimated SA overestimated measured SA but were correlated with measured SA. The results suggest that the estimated SA may a good predictor of measured SA. In the fourth section, three SA estimating methods were applied and evaluated based on number and/or mass concentrations measured by readily available instruments. Estimated SA was derived from particle size distribution by number and was calculated using two different inversion procedures. The estimated SA was compared with the reference SA obtained from the scanning mobility particle sizer and optical particle counter. All estimated SA had qualitatively similar trends to the reference. The results suggest that all estimation methods may be used as an interim solution for the purpose of classifying exposure zones within a workplace