The development of portable chemosensors for atmospheric radicals

The complex photochemical oxidation cycles involved in the degradative removal of
anthropogenic and biogenic hydrocarbons from the atmosphere are mediated by a range
of radical intermediates (e.g. peroxyl radicals). Thus these radicals are of particular
interest in relation to air quality and human health. Speciated measurements of
atmospheric radicals pose considerable challenges to analytical chemists. Owing to their
low concentrations, high reactivity and short lifetimes, free radical species cannot be easily
sampled; therefore direct offline analysis is extremely difficult. Issues such as selectivity,
full structure determination, portability and cost (logistics, power, expertise) remain
challenging obstacles to atmospheric radical analysis.

Within this thesis, the synthesis and development of a series of novel chemosensors is
presented. These are organic trapping compounds that can efficiently and selectively react
with a range of radical species. The chemosensor is designed with the aim of radical
addition to a double bond, resulting in the loss of a stable radical leaving group. The
trapped radical structure is maintained in the reaction products, which are sufficiently
stable for offline mass spectrometry. This approach allows for accurate determination of
the radical structures and is different to traditional spin trapping, with the captured radical
now converted to a stable non radical form.

The developed chemosensors have been tested and evaluated in laboratory and chamber
experiments by application to a range of atmospherically relevant systems (e.g. alkene ozonolysis and reactions of .OH with alkanes), giving key insights into radical selectivity and
reaction mechanisms. They have also been applied to measurements of indoor and
outdoor air, providing evidence for the function of this system at atmospheric radical
concentrations.