Alam, Mohammed Salim (2011)
Ph.D. thesis, University of Birmingham.
The gas-phase reactions of ozone with alkenes can be significant sources of free radicals (OH, HO2 and RO2) in the Earth’s atmosphere. While there are a number of quantitative indirect OH and HO2 yield measurements from ozonolysis in the literature, obtained, for example, through the use of radical tracer / scavenger species, few direct observations have been reported. This thesis presents the first direct measurements of OH and HO2 by Laser Induced Fluorescence for a homologous series of alkenes. The radical and stable products from ethene, propene, 1-butene, 2 methylpropene, cis-2-butene, trans-2-butene and 2,3-dimethyl-2-butene ozonolysis have been observed. The experiments were carried out in the EUPHORE atmospheric simulation chamber, utilising various instrumentation including Fourier Transform Infrared Spectroscopy and Peroxy Radical Chemical Amplification. The alkene-ozone reaction systems were investigated with and without an OH radical scavenger and as a function of humidity. The results were interpreted through detailed chemical chamber box modelling, incorporating the Master Chemical Mechanism degradation scheme for each specific alkene, supplemented with a more explicit representation of the alkene-ozone reaction mechanism. The observed yields are interpreted in terms of branching ratios for each channel within the postulated alkene ozonolysis mechanism, and their implications for atmospheric radical production were considered.
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