The objective of this research area is to study key reactions relevant to atmospheric chemistry, climate change and remote sensing.
The main experimental apparatus used is a flow-tube interfaced to a photoelectron spectrometer. This is used to measure reaction rate constants and branching ratios of atom-molecule and molecule-molecule reactions of atmospheric importance. Reaction mechanisms are also investigated through detection and characterisation of reaction intermediates with uv photoelectron spectroscopy and infrared matrix isolation spectroscopy. This project is also supported with appropriate molecular orbital calculations.
Particular attention is currently being given to the study of reactions of atmospheric importance involving dimethyl sulphide and ozone. For example, in the remote marine boundary layer, where contributions from anthropogenic SO2 are small, gas-phase oxidation of DMS is the most important source of oxidized sulphur compounds---notably SO2, methanesulphonic acd (MSA), dimethylsulphoxide (DMSO) and sulphuric acid. Through the production of sulphuric acid, it has been proposed that atmospheric oxidation of DMS may lead to aerosol production and cloud formation, and hence reduction of the solar radiation reaching the earth. This negative feedback to the earth’s radiative balance is the basis of the CLAW hypothesis. The mechanisms of reactions of DMS with key atmospheric reagents such as Cl, Cl2, BrCl, Br2,OH and NO3 are being investigated and the rate constants of these reactions will be measured. The information derived will then be used in atmospheric modelling.
Ozone-alkene reactions are also currently being investigated using the flow-tube interfaced to a photoelectron spectrometer. Ozone plays important roles in the urban atmosphere and the stratosphere, and ozone reactions with alkenes are important removal pathways in the urban atmosphere. Of particular importance is the production of the OH radical and the Creigee intermediate. The mechanism of production of these reactive intermediates is currently being investigated.