The atmospheric oxidation of volatile organic compounds (VOCs) influences the production of tropospheric ozone and secondary organic aerosol (SOA) with consequences for human health and global climate. Isoprene emitted by vegetation is the dominant VOC in many environments. However, both the ozone- and SOA-forming potential of isoprene remains uncertain. Modeled ozone production from isoprene is highly sensitive to the uncertain mechanistic representation of nitrogen oxides (NOx). In addition, "bottom-up" calculations based on isoprene emission data and chemical mechanisms underestimate SOA concentrations in isoprene-dominated environments. These gaps in understanding constrain the accuracy of air pollution and climate models. While the initial set of reactions that follow the OH radical attack on isoprene have been reasonably well characterized, the subsequent chemical processing of these first generation products (also known multi-generation steps) have received considerably less study and many of the key kinetics parameters that are required for quantitative prediction have not been characterized. This project will investigate the gas- and particulate-phase chemistry of the multi-generation isoprene oxidation products. Specifically, it will evaluate (a) the kinetics and products of the OH radical-initiated reactions of the organic nitrates formed as first-generation products of OH + isoprene, (b) kinetics and products of the OH radical-initiated reactions of dihydroxy-epoxides formed from OH + isoprene, (c) products of OH + methacrolein, including the H-atom abstraction/OH addition branching ratio, and (d) the esterification kinetics of 2-methylglyceric acid and 2-nitrato-2-methylglyceric acid (previously identified as components of isoprene-derived secondary organic aerosol), and of the reverse hydrolysis reaction. The gas-phase experiments will utilize the turbulent flow chemical ionization mass spectrometry technique, which allows OH and NOx levels to be controlled independently. The particulate-phase experiments will utilize bulk solution/NMR and aerosol chamber/aerosol scrubbing/NMR techniques.
Results of this research effort will help improve current predictive capabilities for atmospheric chemistry and thereby facilitate informed public policy decisions regarding mitigation strategies for regional air pollution and climate change. This project will also contribute towards the development of the human resources necessary for the nation's scientific enterprise. The direct involvement of undergraduate students in original research will help prepare them for future careers in science as well as contribute to the increasingly interdisciplinary nature of the science experience at Oberlin College. The project will take place at an institution that is a national leader in the area of undergraduate science education and research and that has had an enduring commitment to increasing the number of underrepresented students in the sciences.
