10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Comparison of Composition and Volatility of Soa Formed from Oxidation of α-Pinene and Scots Pine Emissions
ARTTU YLISIRNIÖ, Angela Buchholz, Claudia Mohr, Andrew Lambe, Celia Faiola, Eetu Kari, Taina Yli-Juuti, Sergey Nizkorodov, Douglas Worsnop, Siegfried Schobesberger, Annele Virtanen, University of Eastern Finland
Abstract Number: 1234 Working Group: Oxidation Flow Reactor: Development, Characterization, and Application to Aerosols
Abstract Secondary organic aerosol (SOA) formed via oxidation of volatile organic compounds (VOCs) is composed of numerous chemical compounds with different functionalities. These compounds dictate chemical and physical properties of the particles, such as hygroscopicity, viscosity and density. A major part of the chemical complexity of SOA stems from the diversity of the initial VOCs and how these compounds are exposed to different oxidative conditions.
In this study, we investigated how differences in oxidative conditions alter volatility and composition of resulting SOA, when particles were formed from oxidation of either α-pinene or Scots Pine VOC emissions. VOCs were introduced into an Aerodyne PAM oxidation flow reactor (OFR). Volatility and composition of the formed SOA particles were measured utilizing a filter inlet for gases and aerosols on a time-of-flight chemical ionization mass spectrometer (FIGAERO-ToF-CIMS) using iodide ionization. The particles were additionally monitored with an Aerodyne aerosol mass spectrometer (AMS). VOC emissions from Scots Pine seedlings were monitored by proton transfer reaction and gas chromatography mass spectrometry (PTR-ToF-MS, GC-MS).
For α-pinene emissions, we used three different oxidative conditions in increasing trend of oxidative strength termed “low”, “medium” and “high”. Due to varying emission profile from Scots Pines we used fixed oxidative conditions comparable to “medium” case in three separate tree emission experiments and stronger oxidative conditions in one tree emission experiment. The α-pinene results show clear correlation between strength of oxidative conditions and volatility of the resulting SOA: The volatility of the particle phase decreased by ~3 orders of magnitude and approximate O:C increased from 0.65 to 0.9 as the level of oxidative exposure increased. The Scots Pine experiments demonstrate the importance of sesquiterpenes in the oxidation processes as emissions from the trees consisted of 20-50 % sesquiterpenes by mass concentration, which are within the range of values measured from Scots pine emissions in the field. The sesquiterpene-influenced SOA had lower volatility than for any of the α-pinene experiments, even when resulting from oxidative conditions comparable to “medium” exposure.
These results are important for understanding formation and transformation of SOA particles in the atmosphere, since coniferous tree emissions are often assumed to be mostly α-pinene and other monoterpenes.