Development of a semivolatile aerosol dichotomous sampler

Abstract

This dissertation consists of three main sections which report the procedures used to develop the semivolatile aerosol dichotomous sampler (SADS) and their results. The first section describes the theoretical background of SADS and the validation of its performance using numerical simulations and experimental data. SADS was proposed as an alternative method to overcome some of the problems of existing personal sampling methods such as evaporative loss during filter sampling. The main difference between virtual impactors and the SADS was the inverted flow ratio between the major and the minor flow. Sampling in the SADS settings gave a lower cutsize in both numerical simulations and experimental results. The second section reports the results of an optimization procedure for SADS and experimental confirmation with the optimized sampler. Using numerical modeling, the relationships between four major design and operating parameters significantly affecting the performance of the SADS and four performance parameters were expressed in polynomial equations. Utilizing an optimization procedure, values for the major parameters giving the best performance were determined and used as the base model for optimizing minor parameters. Five minor parameters were then investigated for their possible contribution to better performance of the SADS. Experimental tests confirmed that the performance of the new sampler was improved although not as much as expected from the numerical simulation. In the third section, the sampling performance of SADS was compared with existing vapor and particle sampling methods. Seven different test fluids were used to generate test droplets and the concentrations and composition in each phase were evaluated using gas chromatography. Combined vapor and particle concentrations for each test aerosol were not statistically different from one another as a function of test method. However, the particle concentrations estimated using the SADS were statistically higher than those from the other methods. In the tests of a chemical mixture and oil mists, a similar pattern of vapor/particle concentration ratio to the individual compounds was observed. SADS worked better than a filtration method and measured higher particle concentrations than other methods.