Multiphase Reactivity of Atmospheric Organic Radicals: Gas- vs. Liquid- vs. Particle-phase Chemistry

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This award is supported by the Chemistry Division's Environmental Chemical Sciences Program. Prof. Jesse Kroll and William Green and their graduate and undergraduate students study the reactions of highly reactive species in the atmosphere, called radicals, with organic compounds. Many environmental chemical processes central to human health, ecological health, and climate occur via the oxidation of organic compounds. This includes the chemical reactions that control the levels of air and water pollutants. The reaction mechanisms can be extremely complex, involving a large of number of chemical intermediates and products. Highly reactive radical intermediates, organic peroxy radicals (RO2) and alkoxy radicals (RO), are formed. These radicals can react via a number of channels, and form a wide range of products. This project aims to improve our understanding of the rates and the products of these reactions. The focus is on how the reaction conditions may control such reactivity. This understanding can ultimately lead to improved models of a wide range of important environmental processes. This enables better predictions and ultimately more informed policy decisions. This project involves both experimental (laboratory) and computational (modeling) studies of RO and RO2 radical reactivity under a wide range of environmental conditions. In the experiments, the radicals are generated by photolysis of appropriate precursor molecules. This is done in the gas phase (using a flow reactor), the bulk liquid phase (using a liquid batch reactor), and within submicron aerosol particles (in an aerosol flow tube). Products are detected primarily by two instruments, an aerosol mass spectrometer for the condensed-phase products and a chemical ionization mass spectrometer for the gaseous products. The laboratory studies are carried out in parallel with the modeling work. This links rates and product distributions with detailed chemical mechanisms. Computational tools include quantum-chemical calculations of structures and energies, calculations of reaction rates, and chemical kinetic modeling of complex reaction mechanisms using the Reaction Mechanism Generator.