| dc.description.abstract | The objective of this research is to develop novel automated gas chromatographic (GC) systems aiming at performing unattended analysis of volatile organic compounds (VOCs). The content comprises of two parts. The first part describes a series of innovated heart-cut GC techniques, which stem from the applications of the Deans switch. The second part addresses the actual employment of the developed GC system in the field.
To measure the full range of VOCs from C2 to C12 and to increase the versatility of the system, the Deans switch was adopted as the core for developing a series of 2-D heart-cut techniques. Methods were developed to add now roles for the Deans switch in 2-D GC applications. In one design, the Deans switch was controlled in a manner to temporary hold-up fluents in the pre-column and, thus, allowed peaks to emerge in the desired retention windows. As a result, peaks from two columns of a Deans switch can be merged into a single flame ionization detector (FID) without overlapping. This concept is termed ?§peak tailoring??.
In the second design, dual detectors were connected to the forth-mentioned system. Two types of compounds, i.e., VOCs and halocarbons, can be measured simultaneously by FID and electron capture detection (ECD), respectively. The most prominent merit arising from this configuration is to exploit atmospheric CFC-113, whose concentration has been proven steady in the atmosphere, as the ?§intrinsic?? to validate the stability of the continuous measurements.
In the third desing, the Deans switch was developed into an adjustable splitter. This device splits the fluents to any desired ratio between two columns at any desired only via the adjustment of the auxillary flow. Under this concept, two columns of different phases, i.e., DB-1 and Cyclodex?VB columns, were adopted to successfully resolve the structural isomers of some mono-aromatics.
The second part of the thesis addresses the characteristics of ambient VOCs and the ozone formation mechanism in the Pearl River Delta (PRD), China based on a measurement campaign. Discussion will then focus on the relationship between ozne and VOCs based on the observation from the Photochemical Assessment Monitoring Station (PAMS) in central Taiwan.
Results from the PRD campaign revealed that vehicular exhaust is the main source of VOCs in Guangzhou. Using the ratio of ethylbenzene to m,p-xlene as an effective age indicator, it is found that the air in Xinken is substantially photochemically processed than that in Guangzhou, consistent with the less alkenes found in Xinken than in Guangzhou. The consistency in time and amplitude between the peaks of ozone and age indicator provides a strong evidence to tie ozone to photochemistry of VOCs in the downwind area of PRD.
Data from PAMS in central Taiwan revealed that high correlation between ozone and the ratios of ethylbenzene to m,p-xlene was found. The aging concept was then usd to explain the high ozone phenomena in downwind areas of central Taiwan. Principal component analysis (PCA) and cluster analysis were also employed to classify sources and their contribution to the observed VOC species and their abundance. Motor vehicular exhaust was found to be the main contributor of ozone formation in this area. | en_US |