Dixon, S.L.; (2005) Instrumental development for understanding atmospheric chemistry and kinetic studies of chlorine oxide dimerisation. Doctoral thesis , University of London.

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Abstract

Numerous current environmental problems result from changes to the trace gas composition of the Earth's atmosphere. Issues such as smog formation, acid rain and stratospheric ozone depletion all result from the chemical transformation of pollutants in the atmosphere and understanding the nature and rapidity of these chemical changes is consequently an important goal of atmospheric science. Laboratory studies of the kinetics and product channels of important atmospheric reactive species - atoms and free radicals - aim to provide data for inclusion into numerical models to simulate changing atmospheric compositioa Typically, the limitation of such laboratory studies is the sensitivity required for monitoring very low concentrations of very short-lived gas phase species. The work described in this thesis addresses mislimitation in new instrument development and in application of an existing instrument to studies of reactions of the atmospherically important CIO free radical. This thesis therefore describes two principal areas of research. In the first part, the design, construction, and testing of an experimental technique for the study of gas phase chemical reactions in a flow system are detailed. This apparatus consists of a conventional discharge flow tube in which reactions take place, coupled to a novel detection system This detection, based upon chemical ionisation mass spectrometry (CIMS), uses a novel chemical ionisation scheme using proton transfer from H3+ ions. A high-pressure electrical discharge system using H2 has been developed and used as the source of H3+ An electrostatic ion guide has also been designed and tested to transport ions efficiently from their region of interaction with the gas under study, to the detector. Experiments to characterise the detection efficiency and instrumental sensitivity have been carried out, along with studies of a variety of chemical systems.

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