Synthetic, Experimental, and Computational Constraints on Pinene Secondary Organic Aerosol Formation

CHRISTOPHER KENSETH, Jing Chen, Olivia Hakan, Nathan Dalleska, Henrik Kjaergaard, Brian Stoltz, Paul Wennberg, John Seinfeld, Joel A. Thornton, University of Washington

     Abstract Number: 412
     Working Group: Aerosol Chemistry

Abstract
For decades, advanced mass spectrometric techniques have been employed to infer structures and develop formation mechanisms of molecular products in secondary organic aerosol (SOA) derived from the oxidation of pinene. These structures and mechanisms have been widely adopted (e.g., in explicit chemical mechanisms) yet remain largely unconstrained, leading to potential misinterpretation and significant uncertainty with respect to the composition, properties, and associated impacts of pinene SOA. In this work, we unambiguously determine the structures of the most abundant monomeric and dimeric products identified using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) in SOA from ozonolysis of α-pinene and β-pinene through independent synthesis of authentic standards. Based on targeted laboratory experiments featuring a selectively deuterated α-pinene isotopologue and using iodide-adduct chemical ionization mass spectrometry (I-CIMS) and LC/ESI-MS for analysis of molecular composition together with quantum chemical calculations of multigenerational α-pinene peroxy and alkoxy radical chemistry, we propose the most likely gas- and/or particle-phase formation mechanisms, which account for the observed H/D kinetic-isotope effects. These insights provide missing links that rationalize a number of observations from past studies and tie the atmospheric degradation of pinene to the production of low-volatility compounds capable of driving particle formation and growth.