AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Chemical Characterization of Organic Aerosol in a Northern Michigan Forest: Investigating Oxidation Products and Pathways
JENNA DITTO, Emily Barnes, Masayuki Takeuchi, Gamze Eris, Peeyush Khare, Nga Lee Ng, Drew Gentner, Yale University
Abstract Number: 47 Working Group: Aerosol Chemistry
Abstract Highly functionalized biogenic organic compounds are known to be a major component of organic aerosol in both remote and urban environments. However, little is known about the identity of many of these compounds, and their impact on local and regional air quality is poorly understood. In this study, we chemically speciate a variety of PM10 organic aerosols collected in July 2016 at the PROPHET field site in Northern Michigan. Oxidation products of varying volatility were analyzed via liquid chromatography coupled with electrospray ionization and quadrupole time-of-flight mass spectrometry (both MS and MS/MS analysis), as well as by gas chromatography coupled with electron ionization mass spectrometry. While the majority of detected compounds have an oxygen-to-carbon ratio (O/C) ranging from 0.2-0.5, compounds with O/C ratios ranging from 0.5 to greater than 1.0 were also observed. We characterize and propose chemical structures for a diverse set of functionalized compounds formed in this forested environment, including highly oxygenated organics, organic nitrates, and organic sulfates. Products observed during the day and at night are contrasted, and we examine possible formation pathways for these compound classes based on elemental ratios and proposed structures. In addition, we compare ambient aerosol products from the PROPHET campaign to chamber oxidation experiments, with a focus on nitrate radical oxidation of alpha- and beta-pinene. Similarity between many organic nitrate compounds observed in chamber experiments and those observed in ambient air suggests the prominence of nitrate radical oxidation at the PROPHET field site. Many nitrated products were observed at night, when nitrate radical oxidation is expected, as well as during the day, suggesting sufficient stability of certain products to persist into the daylight hours as well as additional daytime formation through NOx-dependent pathways.