I’m a physical chemist researching heterogeneous free radical reactions at the Chemical Dynamics Beamline of the ALS. Currently I am studying the reactions of simple radicals (such as OH) with liquid and solid organic aerosol droplets at atmospheric pressure. Despite the high relevance of such particle-radical reactions to combustion and atmospheric chemistry, the details of the chemical reaction mechanisms involved are still poorly understood, in large part due to the complex radical chain cycling chemistry which takes place within the particle. Typically radical reaction mechanisms are elucidated by monitoring the reactants and products using a mass spectrometer. However, conventional ionization techniques (such as electron ionization) cause the large organic molecules of the aerosol droplets to fragment, causing difficulty in differentiating between reactants. The aim of this research is therefore to combine the “soft” ionization technique of VUV photoionization available at the ALS’s Chemical Dynamics Beamline with kinetic modeling in an attempt to develop a much more detailed understanding of the chemical mechanisms of these aerosol reactions.