Year

1997

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

Studies in recent years have revealed that the global atmosphere is undergoing rapid change due to anthropogenic activities, potentially leading to climate change through greenhouse warming, and to harmful stratospheric ozone dq)letion. There is a need for more and better measurements of the atmospheric trace gases implicated in these processes, so that the global anthrqpograic impact can be quantified and, if possible, minimised. The three main anthropogenic greenhouse gases are carbon dioxide, methane and nitrous oxide. Nitrous oxide is also implicated in stratospheric ozone depletion. Carbon monoxide, while not directly a greenhouse gas, is intimately connected with the oxidative state of the atmosphere. Measurements of the background atmosphere mixing ratios and of biosphere-atmosphere fluxes of trace gases typically employ seme ensemble of Gas-Chromatogr^hy (GC), Non-Dispersive Infrared (NDIR) spectroscopy and Tunable Diode Laser (TDL) spectroscopy instrumentation. If, in addition, stable isotope ratio data are to be retrieved, Isotope-Ratio-Mass-Spectrometry (IRMS) instrumentation is required. These iostruments all provide high-predsiou measurements. However, their usual singlespecies focus, their variety of deteaor response functions, calibration requirements, varying degree of mobility, as well as their complexity and expense, seriously constrains the accumulation of data in both laboratory and field investigations. This thesis reports the development of a mediod of trace gas and isotope ratio analysis based on Icm"^ resolution FITR spectroscopy, deployable in both laboratory and field implications. The species CO2, CH4, CO and N2O may be analysed simultaneously in a single air sample using this method. Its mixing ratio analytical precision is in all cases superior to or competitive with that of the more usual methods mentioned above. In addition, the FTIR instrument may be used to measure the stable isotope ratio of CO2 in ambient air to a gepphysically useful degree of precision; still exceeded, however, by that attainable using IRMS. The novel FTIR method relies on calibration using synthetically calculated absorbance spectra and a chem(Hnetric multivariate calibration algorithm. Classical Least Squares (CLS). Careful experimental design and control of the instrument environment also contributes to the high degree of precision achieved.

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