AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Molecular Characterization of Biogenic SOA Using Online Extractive Electrospray Ionization Mass Spectrometry: On the Fate of Condensed Phase ELVOC
FELIPE LOPEZ-HILFIKER, Veronika Pospisilova, Ugo Molteni, Mao Xiao, Josef Dommen, Andre Prévôt, Urs Baltensperger, Jay Slowik, Paul Scherrer Institute
Abstract Number: 291 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Recent measurements of the oxidation products from biogenic precursors by chemical ionization mass spectrometry (CIMS) have revealed a large source of extremely low volatility organic molecules (ELVOC) formed at high yield. These molecules can contribute to new particle formation and subsequent particle growth despite their low gas phase abundance. Measurements of particle composition and volatility by CIMS is largely consistent with a significant source of secondary organic aerosol (SOA) formed from the condensation of initially low volatility organic vapors; however, the tendency of these molecules to undergo ionization-induced fragmentation and/or thermal decomposition has to date prevented their direct measurement. As such, the fate of highly oxidized organics formed in the gas phase in the condensed phase remains an open question.
Here, we present the first direct online measurements of individual organic aerosol components at atmospherically relevant particle mass loadings without thermal decomposition or ionization-induced fragmentation, using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) recently developed at PSI. We focus on the measurement of highly oxidized, low volatility organic molecules and oligomers, which are formed rapidly from biogenic precursors and the fate of these molecules in the particle phase during ageing. To investigate these particle-phase formation and ageing mechanisms the EESI-TOF was deployed at the PSI atmospheric simulation chamber where biogenic precursor compounds were oxidized under a variety of conditions.
Our measurements utilizing the EESI-TOF and a variety of biogenic precursor molecules provide a new level of molecular insight that allows the direct assessment of particle phase oligomerization, fragmentation and ageing reactions. We discuss these individual and combined effects on SOA formation, lifetime and response to atmospheric changes as well as the implications of these findings for measurements of gas-particle partitioning and validation of SOA formation models.