AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Measurements and Modeling of Isoprene Photooxidation Products: The Role of Oligomeric Material and Particle Phase Reactions
EMMA D'AMBRO, Felipe Lopez-Hilfiker, Claudia Mohr, Cassandra Gaston, Ben Lee, Jiumeng Liu, John Shilling, Rahul Zaveri, Avram Gold, Zhenfa Zhang, Jason Surratt, Joel A. Thornton, University of Washignton
Abstract Number: 395 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Isoprene is the predominant non-methane volatile organic compound emitted globally with the potential to produce large quantities of secondary organic aerosol (SOA) affecting climate, air quality, and human health. However, the mechanisms controlling isoprene SOA formation remain uncertain. We present novel measurements and modeling of isoprene SOA formation observed in environmental simulation chambers using dry neutral seed particles, thereby suppressing IEPOX multiphase chemistry, at a variety of atmospherically relevant conditions. A high resolution time of flight chemical ionization mass spectrometer utilizing iodide adduct ionization coupled to the Filter Inlet for Gas and AEROsol (FIGAERO) allowed for the simultaneous online sampling of the gas and particle composition. Under high HO2 and low NO conditions, SOA yields reached > 10% and dihydroxy dihydroperoxides and related products were major components (~50%). A similarly large fraction of SOA was also detected as smaller compounds that desorbed at unexpectedly high temperatures, indicative of thermal decomposition of lower volatility components, likely larger molecular weight oligomers. A detailed chemical box model based on the University of Leeds Master Chemical Mechanism, with several custom updates and an online Raoult’s law gas-particle partitioning module accurately reproduces the time evolution and approximate quantity of SOA, as well as a dominant role for dihydroxy dihydroperoxides, in both our chamber experiments and those conducted in other chambers. However, the predicted SOA composition and evaporation kinetics do not adequately reflect the measurements. These findings, together with observed composition evolution over time, strongly suggest efficient particle phase organic chemistry, in the absence of aqueous-phase acidity, leads to oligomeric material which accounts for ~50% of the SOA mass formed after 3-5 hours. We use these insights and observations of the same SOA components made during the SOAS field campaign to assess the importance of isoprene photo-oxidation as a local SOA source.