The overall objective of this proposal is to develop quantitative chemical mechanisms for the gas phase and heterogeneous/multiphase reactions involved in the formation of secondary organic aerosol (SOA) from the hydroxyl (OH) radical-initiated reactions of selected classes of alkanes and alkenes and their reaction products over a wide range of conditions, and to use these mechanisms with information on gas-particle-wall partitioning to develop comprehensive models of SOA formation and oxidative aging. The approach will involve experimental studies of OH radical-initiated reactions over a wide range of carbon numbers. These compounds contain most of the basic structural features present in atmospheric volatile organic compounds (VOC) and SOA. Reactions will be conducted in a large, Teflon environmental chamber under conditions representative of polluted and clean air, and the effects of relative humidity and particle chemical composition, acidity, and mass loading on the reactions will be explored. Reaction products present in the gas and particle phases will be identified and quantified using real-time and offline methods including thermal desorption particle beam mass spectrometry, liquid and gas chromatography coupled to a variety of detectors, and spectrophotometry without and with the aid of functional group derivatization. Experiments will also be conducted in the environmental chamber and in smaller reactors with authentic or surrogate reaction products to investigate gas-wall partitioning, vapor pressures, and activity coefficients of reaction products, as well as the kinetics and equilibria of their potential heterogeneous/multiphase reactions. The results will be used to develop comprehensive kinetic models of these processes that incorporate gas phase and heterogeneous/multiphase reactions and gas-particle-wall partitioning.
Broader impacts of the data obtained on reaction products and branching ratios for gas phase reaction pathways, heterogeneous/multiphase reaction kinetics and equilibria, and gas-particle-wall partitioning will be their application to many other VOC-oxidant systems because of the similarity in fundamental reaction pathways, products, and functional groups. Because of the widespread use of Teflon chambers, the results will be useful for evaluating and improving methodology and interpretation of environmental chamber studies, which provide valuable data that is widely used by the atmospheric chemistry and aerosol modeling community, as well as improving chemical reaction mechanisms and SOA models that serve as modules in 3-dimensional air quality models. These models are used to evaluate potential effects of gases and particles on regional visibility, human health, ecosystems, and climate. This project will also educate two or more graduate students and serve as the basis for their Ph.D. dissertations, and provide research opportunities for undergraduate students. Students will be trained in the areas of organic analysis, kinetics, and atmospheric gas phase and aerosol chemistry, and, depending on their degree program, will also be educated more broadly in chemistry, environmental toxicology, or environmental science. Students will publish research results in scientific journals and attend and present results at local, regional, and national conferences. As a result, students will be well prepared for future careers in industry, academia, or a government agency working on environmental problems. Data and results will be disseminated through publications, conference presentations, and a website, which will expand the value and use of the data.
