Abstract

Criegee biradicals (RCH2OO) are key reaction intermediates in the atmospheric degradation of unsaturated volatile organic compounds (VOCs) and have been implicated in radical chain branching reactions in combustion of the biofuel dimethyl ether (DME). In the atmosphere, Criegee biradicals play an important role in the production of OH and HO2 radicals, and the OH source from Criegee biradicals has been shown to be particularly important in urban environments in winter when photolytic sources are low.

Recent interest in Criegee intermediates has largely focused on the kinetics of their bimolecular reactions. However, unimolecular decomposition reactions of stabilised Criegee intermediates are potentially significant as loss mechanisms in the atmosphere, and unimolecular decomposition of CH2OO is likely to be important under combustion conditions. In addition, the atmospheric impacts of Criegee intermediates are dependent on the nature of the reaction products, which are subject to large uncertainties.

Current work in Leeds is focussed towards the measurement of direct reaction kinetics for Criegee intermediates using broadband time-resolved ultraviolet absorption spectroscopy, and the development of time-resolved infrared absorption spectroscopy for the determination of product yields. Recent investigations of the reactions of CH2OO with SO2 and NO2 will be discussed, and the results of a recent study of the unimolecular decomposition reactions of CH2OO and CH3CHOO , conducted in collaboration with groups at the Sandia National Laboratory, US, will be presented.