Laboratory studies of halogen-containing and organic species of atmospheric importance

Thesis

This thesis describes laboratory studies of the kinetics of some reactions of atmospheric significance. The species of interest were Cl atoms, IO radicals and several organic compounds. In particular, the chemistry of acetone and the acetonylperoxy radical was investigated. These species are of importance in the troposphere and the stratosphere, where they may influence the concentrations of HO_x, NO_x and O₃.

The experiments were performed using low-pressure discharge-flow tubes coupled to a variety of detection techniques, including conventional methods such as resonance fluorescence (RF) and electron-impact mass spectrometry (EEVIS). However, much of the thesis is concerned with the development of techniques that offer a greater sensitivity and selectivity, namely, laser-induced fluorescence (LIF) and chemical-ionization mass spectrometry (CIMS).

The reactions of Cl atoms with acetone and butanone were monitored with Cl RF. The study of the former reaction was extended in order to obtain information about the chemistry of the acetonylperoxy radical. IO was observed with LIF. This work involved the first reported coupling of IO LIF to a discharge-flow tube. The system was shown to be a suitable method by which to study reactions of IO. The results of these investigations demonstrate that reaction with Cl and IO may be an important sink for several organic compounds in the marine boundary layer.

The design, construction and commissioning of the EIMS system is described. The apparatus was used in an attempt to follow the self-reaction of the acetonylperoxy radical by monitoring the products. The complications that arose during the study illustrated the need for a more versatile form of MS. It was decided to convert the instrument to a CMS system that would allow direct observation of the peroxy radical. The construction of two ion sources, one employing a cartridge of polonium-210 and the other a simple discharge, as well as an electrostatic ion guide, is described. The discharge source was shown to be better suited to the low-pressure conditions.

Authors: Wagner, K

• Peer review status: Peer reviewed
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford