Photooxidation of Biogenically Produced Alkenes: Impacts on HOx, NOx, and Aerosol

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This project will employ state-of-the-art instrumentation to investigate the photo-oxidation of biogenic alkenes and their oxidation products as part of a multi-investigator field program in the forested environment of California's Sierra Nevada, a chemical regime where organic peroxy radicals react with hydrogen peroxide under conditions with relatively low levels of nitrogen oxides (NOx). This regime is currently poorly characterized; previous field observations have suggested that the mechanisms currently used in photochemical models are inconsistent with observed levels of NOX. A triple quadrupole mass spectrometer will be coupled to a custom, selected-ion chemical ionization inlet for real-time analysis of many short-lived, reactive compounds including the organic peroxides that have, to date, been poorly quantified. During the field campaign, a second chemical ionization mass spectrometer will be used to measure, via eddy covariance, the fluxes of hydrogen cyanide, hydrogen peroxide and nitric acid.The results will improve constraints on the mechanisms responsible for 1) production and loss of ozone, 2) the production and fate of organic nitrates, and 3) formation of secondary organic aerosol in Earth's atmosphere, thus providing substantially improved understanding of the nature of the organic chemistry that controls the burden of ozone and aerosol in many regions of the world. The work will involve collaborations with a broad spectrum of scientists, including other atmospheric chemists, meteorologists, and ecologists studying the biochemistry leading to the formation and release of biogenic alkenes from trees. These collaborations will expose graduate students and post-doctoral scholars involved in the work to the breadth of earth science.