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Chemistry of Secondary Organic Aerosol Formation


Yee, Lindsay Diana (2013) Chemistry of Secondary Organic Aerosol Formation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BPKE-M777.


The photooxidation of volatile organic compounds (VOCs) in the atmosphere can lead to the formation of secondary organic aerosol (SOA), a major component of fine particulate matter. Improvements to air quality require insight into the many reactive intermediates that lead to SOA formation, of which only a small fraction have been measured at the molecular level. This thesis describes the chemistry of secondary organic aerosol (SOA) formation from several atmospherically relevant hydrocarbon precursors. Photooxidation experiments of methoxyphenol and phenolic compounds and C12 alkanes were conducted in the Caltech Environmental Chamber. These experiments include the first photooxidation studies of these precursors run under sufficiently low NOx levels, such that RO2 + HO2 chemistry dominates, an important chemical regime in the atmosphere. Using online Chemical Ionization Mass Spectrometery (CIMS), key gas-phase intermediates that lead to SOA formation in these systems were identified. With complementary particle-phase analyses, chemical mechanisms elucidating the SOA formation from these compounds are proposed.

Three methoxyphenol species (phenol, guaiacol, and syringol) were studied to model potential photooxidation schemes of biomass burning intermediates. SOA yields (ratio of mass of SOA formed to mass of primary organic reacted) exceeding 25% are observed. Aerosol growth is rapid and linear with the organic conversion, consistent with the formation of essentially non-volatile products. Gas and aerosol-phase oxidation products from the guaiacol system show that the chemical mechanism consists of highly oxidized aromatic species in the particle phase. Syringol SOA yields are lower than that of phenol and guaiacol, likely due to unique chemistry dependent on methoxy group position.

The photooxidation of several C12 alkanes of varying structure n-dodecane, 2-methylundecane, cyclododecane, and hexylcyclohexane) were run under extended OH exposure to investigate the effect of molecular structure on SOA yields and photochemical aging. Peroxyhemiacetal formation from the reactions of several multifunctional hydroperoxides and aldehyde intermediates was found to be central to organic growth in all systems, and SOA yields increased with cyclic character of the starting hydrocarbon. All of these studies provide direction for future experiments and modeling in order to lessen outstanding discrepancies between predicted and measured SOA.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:secondary organic aerosol, volatile organic compound, alkane, methoxyphenol
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Seinfeld, John H.
Thesis Committee:
  • Wennberg, Paul O. (chair)
  • Seinfeld, John H.
  • Flagan, Richard C.
  • Okumura, Mitchio
Defense Date:10 April 2013
Record Number:CaltechTHESIS:03162013-090820386
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 3 adapted for ch. 4 adapted for Appendix A adapted for Appendix B 2012DOIArticle adapted for Appendix C 12-151-2012DOIArticle adapted for Appendix D adapted for Appendix E adapted for Appendix F adapted for Appendix G
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7521
Deposited By: Lindsay Yee
Deposited On:10 Jan 2014 00:29
Last Modified:03 Oct 2019 23:59

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