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Atmospheric Peroxy Radical Chemistry Studied by Infrared Kinetic Spectroscopy


Hui, Aileen Oyama Ah Yee (2019) Atmospheric Peroxy Radical Chemistry Studied by Infrared Kinetic Spectroscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9H0-1H20.


Peroxy radical (RO2) chemistry plays a central role in atmospheric science. RO2 radicals control the oxidative capacity of the atmosphere and are key intermediates in the cycling of ozone in the troposphere in regions where levels of nitrogen oxides (NOx ≡ NO + NO2) are high. In more remote regions of the Earth where NOx concentrations are low, RO2 loss is dominated by reaction with hydroperoxy (HO2) and other peroxy radicals, leading to removal of reactive radicals from the troposphere. However, for certain species of RO2, reaction with HO2 can also propagate radical chemistry by recycling hydroxyl (OH) radicals, a primary oxidant in the atmosphere. Both HO2 and OH radicals play important roles in atmospheric oxidation reactions. Accurate characterization of various RO2 reactions that contribute to consuming and recycling HOx (HOx ≡ HO2 + OH) are instrumental for understanding the effects of atmospheric composition on climate forcing, air quality, and the global ozone budget.

My thesis work used laboratory studies to characterize gas phase organic peroxy radical (RO2) reactions that are relevant to atmospheric chemistry. The main body of my work focused on studying the self reactions of HO2 and RO2 as well as their cross reactions (HO2 + RO2) using a time-resolved experimental technique called Infrared Kinetic Spectroscopy (IRKS), which combines infrared (IR) and ultraviolet (UV) absorption spectroscopy. Perfect isolation of one specific reaction is generally difficult or impossible due to radical recycling and secondary chemistry, which leads to numerous reactions occurring simultaneously. Thus, although laboratory studies provide controlled environments to study these reactions, the accuracy of the results are highly dependent on the experiment's selectivity and sensitivity to specific transient species. In this work, a new mid-IR (MIR) laser was implemented into the existing apparatus for measuring OH radicals. In addition to UV absorption spectroscopy, the IRKS apparatus was equipped for selective detection of HO2 and OH radicals in the near-IR (NIR) and MIR, respectively.

The kinetics and product yields of a reaction are two important factors for assessing the impact of these reactions on the atmosphere. IRKS was used to study the kinetics of the self reactions of acetylperoxy (CH3C(O)O2) and acetonylperoxy (CH3C(O)CH2O2), as well as their reactions with HO2. The OH and O3 yields from the reaction of HO2 + CH3C(O)O2 were also measured, providing the first parametrization of the temperature dependence of the OH product channel. The temperature dependence of the HO2 self reaction kinetics was re-investigated to resolve discrepancies in the results previously reported in the literature. Furthermore, this work identified and characterized rate enhancement effects on the HO2 self reaction by the adducts of HO2 formed from the reaction of HO2 with methanol (CH3OH), acetaldehyde (CH3CHO), and acetone (CH3C(O)CH3), which were used as radical precursors for HO2, CH3C(O)O2, and CH3C(O)CH2O2, respectively.

Finally, the improved sensitivity of the IRKS apparatus enabled the investigation of fast reaction kinetics. The rate constants of Cl atoms with CH3OH and CH3CHO were measured over a wide range of temperatures. The results were consistent with previously reported values in the literature and additionally validated assumptions that had been made regarding the temperature independence of these reactions. The temperature and pressure dependences of the OH yield from the reaction of CH3CO with O2 were also studied to resolve current discrepancies in the literature. The yield of HO2 from this reaction was also directly measured for the first time.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemical physics, kinetics, atmospheric chemistry, spectroscopy
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Okumura, Mitchio (advisor)
  • Sander, Stanley P. (co-advisor)
Thesis Committee:
  • Miller, Thomas F. (chair)
  • Blake, Geoffrey A.
  • Marcus, Rudolph A.
  • Okumura, Mitchio
  • Sander, Stanley P.
Defense Date:29 November 2018
Funding AgencyGrant Number
Record Number:CaltechTHESIS:01172019-135430092
Persistent URL:
Hui, Aileen Oyama Ah Yee0000-0003-4217-2698
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11345
Deposited By: Aileen Hui
Deposited On:30 Jan 2019 17:43
Last Modified:04 Oct 2019 00:24

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