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Insights on the Formation and Fate of Organic Nitrates in the Atmosphere from Field and Laboratory Observations

Citation

Teng, Alexander Pai-Chung (2017) Insights on the Formation and Fate of Organic Nitrates in the Atmosphere from Field and Laboratory Observations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9RV0KRJ. http://resolver.caltech.edu/CaltechTHESIS:06042017-134711204

Abstract

Alkenes are oxidized rapidly in the atmosphere by addition of OH and subsequently O2, leading to the formation of peroxy radicals. These peroxy radicals react with NO to form organic nitrates through a minor radical-terminating branching pathway. Over large regions of the continental boundary layer, the formation of organic nitrates control tropospheric ozone and the lifetime of NOx. Laboratory investigations described herein show that the yield of nitrates through this pathway is larger than previously described for alkenes, and the yield increases with the number of heavy atoms. This result is used to interpret field observations taken over Houston in the summer of 2013. These measurements show that small alkenes still play a large role in ozone production more than a decade after they had been identified as a causal factor. In further studies, measurements of isoprene hydroxy nitrates (ISOPN) and hydroperoxides, formed from the OH oxidation of isoprene, are used to diagnose the complexities of reversible O2 addition for allylic hydroxy isoprene radicals. It is shown that over most of the atmosphere, isoprene's peroxy radical isomers are in their equilibrium distribution. In this regime, hydroxy peroxy radical isomers comprise approximately 95% of the radical pool, a much higher fraction than in the nascent (kinetic) distribution. Intramolecular H-shift isomerization from the Z hydroxy peroxy radical isomers produced from OH addition to C4 is estimated to be 4s-1 at 297K. While the Z isomer is initially produced in low yield, it is continually reformed via decomposition of the hydroxy peroxy radicals. As a result, unimolecular chemistry from this isomer contributes as much as half of the atmospheric fate of the entire pool of peroxy radicals formed via addition of OH at C4. In contrast, unimolecular chemistry following OH addition at C1 is slower and less important. Field observations of alkyl nitrates over the Southeastern United States during the summer over forested environments show that there are still gaps in our understanding of the organic nitrate budget. The formation of isoprene hydroxy nitrates (ISOPN) is shown to be a dominant NOx loss pathway during the day.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Isoprene, atmopsheric chemistry, peroxy radicals, volatile organic compounds, oxidative mechanisms
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):
  • Wennberg, Paul O.
Group:Wennberg Group
Thesis Committee:
  • Seinfeld, John H. (chair)
  • Okumura, Mitchio
  • Sander, Stanley P.
  • Wennberg, Paul O.
Defense Date:22 February 2017
Funders:
Funding AgencyGrant Number
National Science FoundationAGS- 1240604, CHE-1508526
National Aeronautics and Space AdministrationNNX14AP46G
Record Number:CaltechTHESIS:06042017-134711204
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:06042017-134711204
DOI:10.7907/Z9RV0KRJ
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/jacs.6b12838DOIArticle adapted for Ch. 3.
https://doi.org/10.5194/acp-15-4297-2015DOIArticle adapted for Ch. 2.
ORCID:
AuthorORCID
Teng, Alexander Pai-Chung0000-0002-6434-0501
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10265
Collection:CaltechTHESIS
Deposited By: Alexander Teng
Deposited On:07 Jun 2017 17:37
Last Modified:16 Jun 2017 22:46

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