Understanding of the chemical composition of the atmosphere requires knowledge of its physical and chemical properties, reaction mechanisms and rate constants of the elementary reactions involved. Laboratory experiments involving state-of-the-art techniques in physical chemistry are used to obtain this information, which can be used to interpret atmospheric observations and to predict atmospheric composition and how it affects climate, air quality and the stratospheric ozone layer.
A major current focus is on aerosols and heterogeneous reactions. We use infra-red spectroscopy and particle counting instruments to establish physical and chemical properties of model aerosols generated in the laboratory. We investigate the reactivity of the aerosols towards gases by measurement of the kinetics of uptake of trace gases onto aerosols, and also onto bulk surfaces representative of atmospheric particles, in a flow system coupled to a molecular beam sampling quadrupole mass spectrometer. Currently we are investigating processes on ice surfaces, which are present in the upper atmosphere.
An example is the uptake of HCl on ice surfaces, which is prerequisite to chemical reaction leading to release of active chlorine in the lower stratosphere. The existence of a quasi-liquid layer on the ice surface gives a strong temperature dependence to HCl uptake. We are also studying heterogeneous reactions on salt aerosols, which predominate in the marine and terrestrial boundary layer.
Another aspect of our work is the study of the mechanism of gas phase oxidation of volatile organic species at low temperature, characteristic of the upper troposphere. This involves measurements of yields and product types from photochemically initiated reactions, using gas chromatography, UV and IR spectroscopy.
Our work also involves evaluation and recommendation of kinetic and photochemical data for atmospheric modelling, which is part of an IUPAC project, for which we host the website.