| Popis: |
Chemical characterization of aerosols is essential to understand their health effects in environmental and occupational health studies. There has been a great interest in developing low cost, compact, hand-portable and direct-reading instruments for aerosol monitoring. Microplasma spectroscopy methods, such as laser induced breakdown spectroscopy (LIBS), spark emission spectroscopy (SES) and glow discharge optical emission spectroscopy (GD-OES), have been intensively studied and proved as practical technologies for detecting elemental composition of aerosols. The main focus of this dissertation is to develop a low cost and hand-portable methods for near real-time measurement of elemental concentration of aerosol using microplasma spectroscopy. The dissertation is divided into three parts. In the first part, a corona-based aerosol microconcentrator is designed for efficient concentrating aerosols to a substrate for subsequent analysis using microscale optical spectroscopies. Performance of this corona microconcentrator is determined experimentally by measuring collection efficiency, wall losses, and particle deposition density. An intrinsic spectroscopic sensitivity is determined for the aerosol microconcentrator using SES. Using this intrinsic sensitivity, it is shown that the corona-based microconcentration method provides the best measurement sensitivity compared to alternative particle collection methods, such as filtration, focused impaction using aerodynamic lens, and spot collection using condensational growth. This method has been demonstrated to be very suitable for compact hand-held analytical instrumentation. The second part of the dissertation focuses on the development of various methods for aerosol measurement using corona microconentration method coupled with microscale optical spectroscopies. First, a sensitive method has been developed for real-time measurement of carbonaceous aerosol using LIBS or SES. The measurement system is calibrated and detection limits are determined for total atomic carbon using a carbon emission line at 247.856 nm (C I) for various carbonaceous nanoparticles. Measurements of carbon nanotube aerosol at elevated electrode temperature showed improved selectivity to elemental carbon and compared well with the measurements from thermal optical method (NIOSH Method 5040). Second, a multivariate calibration approach has been developed for simultaneous measurement of multiple elements of aerosol using SES. Partial least squares (PLS) regression is performed to construct the relationship between spectra and elemental mass. The PLS model is applied to predict elemental concentration of welding aerosols, showing good measurement accuracy. Third, the corona aerosol microcoentrator is coupled with glow discharge optical emission spectroscopy (GD-OES), forming a low cost method for semi-continuous analysis of aerosol, compared with methods using LIBS and SES. The spectral features and signal stability of this GD-OES aerosol analysis system are investigated. Analytical performance, such as limits of detection and uncertainty, are determined for several elements, and compared with other aerosol analysis methods that employ microplasma spectroscopies. In the third part, spatial and temporal dynamics of spark microplasma used for aerosol measurement is systemically investigated. The spatial and temporal behavior of carbon emission in spark plasma from carbon black particles is investigated. The plasma parameters, such as excitation temperature and electron density are evaluated using spectroscopic means, and their dependences on interelectrode distance, delay time and pulse energy are presented. |
