| Summary: | 碩士 === 中國醫藥大學 === 職業安全與衛生學系碩士班 === 101 === Ambient ultrafine particles (diameters < 100 nm) are chemically complex mixtures. Because of their small sizes, these particles have little mass and evolve rapidly in ambient air, thus making the measurements of their physicochemical properties a major technical challenge. Nevertheless, as different chemicals exhibit different volatility, direct measurements of the particle volatility could allow us to infer particle’s chemical composition and mixing state. With that in mind, the aims of this study were to develop a volatility tandem mobility analyzer (V-TDMA) system for measuring ultrafine particles’ volatility, to apply the system for assessing the size-dependent volatility as a function of time, and to identify the relative volume fractions of different volatile components.
The developed V-TDMA system includes a TDMA that selects and measures the particle size, a thermodenuder that thermally desorbs volatile compounds from the particles at three different temperatures (26°C, 100°C and 320°C) and then removes them from the gas stream, and a scanning mobility particle sizer and condensation particle counter that measures the number size distribution of particles between 5.5-350 nm. The measurement results were subsequently used for the estimation of particle shrinkage factor (SF) and volatile volume fraction (VF).
A series of quality assurance and quality control measures were taken to characterize the temperature profile, particle losses, sizing precision/accuracy, and volatile particle removal efficiency of the V-TDMA system. The test results suggest that the performance of the V-TDMA system is inline with earlier work. In the field application, the results show that the particle volatility under different temperature was strongly dependent on the particle size but showed little temporal patterns. Overall, the results indicate that ultrafine particles mainly consist of low-volatile compounds and the remaining of minor non-volatile and high-volatile compounds; however, the nucleation mode particles could consist a notable amount of high-volatile compounds.
|
|---|
