Laboratory studies of Criegee radical reactions

Chemicals entering the atmosphere come from a number of sources, but in broad terms are either from human activity or from the biosphere (natural systems). What happens to these chemicals once in the atmosphere is very important of course. If they are toxic they can impact on the health of humans, animals and natural ecosystems. Therefore, it is vital that we understand how pollutants are removed by the atmosphere. One very important removal process involves the so called hydroxyl radical. This is an extremely reactive species that acts like a chemical detergent, destroying pollutants and cleaning up the atmosphere. It has emerged in recent investigations that an important source of the hydroxyl radical must be coming from Criegee radicals. However, these Criegee radicals have been impossible to measure until recently. Work carried out by us, using a facility in the USA, has allowed us to observe a Criegee radical for the first time. In this project we will develop a state-of-the-art experimental system that will allow us to investigate the chemistry of Criegee radicals and therefore to help us to understand how they affect the amount of hydroxyl radical is present in the atmosphere. Such work will not only improve our understanding of the urban environment but will also have implications for climate studies as well. Reactions of Criegee intermediates, over a wide range of pressure and temperature, are of importance in atmospheric chemistry. The proposed UV-PE apparatus will be the first of its kind and will enable us to carry out a range of experiments to study reactions of these radicals that, as far as we are aware, no one else in the world can do. To demonstrate how versatile the apparatus is we propose a carefully designed set of experiments to look at the source and fate of Criegee radicals in the troposphere. Quantum chemistry calculations of the reactions studied will provide detailed understanding of their mechanisms and the kinetic data will be incorporated into models describing the troposphere and compared with available measurements.