Abstract View
Formation and Aging of Carboxylic Acids and Dimer Esters in α-Pinene and β-Pinene Secondary Organic Aerosol
CHRISTOPHER KENSETH, Yuanlong Huang, Nicholas Hafeman, Nathan Dalleska, Brian Stoltz, John Seinfeld, California Institute of Technology
Abstract Number: 513
Working Group: Aerosol Chemistry
Abstract
Multifunctional carboxylic acids and dimer esters have been identified using advanced mass spectrometric techniques as significant components of secondary organic aerosol (SOA) formed from oxidation of α-pinene and β-pinene. Due to a lack of authentic standards, however, structures of these SOA molecular products are inferred from accurate mass/fragmentation data and, therefore, mechanistic understanding of their formation and aging remains unconstrained. Here, informed by detailed structural analyses (MS and MS/MS, 13C isotopic labeling, and H/D exchange), we synthesize the first authentic pinene-derived dimer ester and elucidate its formation mechanism from a series of targeted SOA formation experiments using chemical ionization mass spectrometry (CIMS) and liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) for analysis of gas- and particle-phase composition. Additionally, we investigate the aqueous-phase (photo)chemistry (kinetics, products, and mechanisms) of six recently synthesized, pinene-derived carboxylic acid and dimer ester homologues at cloudwater-relevant concentrations as a function of pH using LC/ESI-MS. These studies provide a missing link tying the atmospheric degradation of α-pinene and β-pinene to the observed formation of low-volatility compounds capable of driving particle formation and growth, as well as key insight into the dependence of aqueous-phase photochemical processing on molecular size/functionality and applicability of aqueous-phase structure-activity relationships (SARs).