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Cavity Ring-Down and Multi-Pass Spectroscopies for Methane Source Attribution and Chemical Kinetics Studies


Shen, Linhan (2018) Cavity Ring-Down and Multi-Pass Spectroscopies for Methane Source Attribution and Chemical Kinetics Studies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/WE40-5W54.


Methane is the most abundant hydrocarbon in the Earth atmosphere, is also an important greenhouse gas, energy source, and microbial metabolic energy source and product. With the rapid increase of atmospheric methane concentration, it has become very important to quantify methane emissions from different sources. This thesis describes the applications of cavity ring-down applications on atmospheric ethane measurements and measurements of doubly substituted methane for methane source attributions. We also present our work on chemical kinetics studies of an alkene ozonolysis intermediate, Criegee intermediate, using a multi-pass absorption technique.

In Chapter 2, we demonstrated the performance of a continuous-wave (cw) interband cascade laser (ICL) based mid-infrared cavity ring-down spectroscopy (CRDS) sensor for atmospheric ethane (C2H6) detection. A 3.36 µm cw ICL with an was used to target two ethane absorption bands at 2976.788 cm-1 and 2983.383 cm-1. This technique utilizes the long effective pathlength (~ 4.5 km) of CRDS to increase sensitivity of atmospheric ethane detection. Our spectrometer can measure atmospheric ethane concentration as low as 200 pptv at standard temperature and pressure. We have used this instrument to measure the atmospheric ethane composition in ambient air collected in Pasadena, California. We have utilized this instrument to aid in the study of soil microbial response post the Porter Ranch gas leak. Results were shown in Chapter 3.

In Chapter 4, we demonstrate high sensitivity measurements of both 13CH3D and 12CH2D2 isotopologues using a high precision and high resolution spectroscopy technique, frequency stabilized cavity ring-down spectroscopy (FS-CRDS). Measurements of the abundances of doubly-substituted methane isotopologues (13CH3D and 12CH2D2) are important in methane source attributions. Currently, methods developed for 13CH3D and 12CH2D2 measurements have been mostly focused on the use of isotope ratio mass spectrometry (IRMS), which faces the challenges of mass resolutions. In this work, we focus on measuring these low abundant methane isotopologues optically, taking advantage of the distinct absorption features of them. This technique can be used as a potential complement to IRMS measurements for its ability to measure abundances of rare methane isotopologues with a short time average (~1 hour average per isotope ratio measurement).

In Chapter 5, we utilized our IR kinetic spectroscopy (IRKS) apparatus to study the formation of HCO radicals from the smallest Criegee Intermediate (CH2OO), which is an important intermediate from oznolysis of the smallest alkene.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Methane Isotopes; Criegee Intermediate; Cavity Ring-down 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
Thesis Committee:
  • Blake, Geoffrey A. (chair)
  • Marcus, Rudolph A.
  • Eiler, John M.
  • Christensen, Lance E.
  • Okumura, Mitchio
Defense Date:3 November 2017
Record Number:CaltechTHESIS:04122018-141241438
Persistent URL:
Shen, Linhan0000-0003-3871-655X
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10804
Deposited By: Linhan Shen
Deposited On:24 May 2018 23:33
Last Modified:04 Oct 2019 00:20

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