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DEVELOPMENT OF A NOVEL HETEROGENEOUS KINETICS REACTOR AND
CHEMICAL CHARACTERIZATION OF SOOT PARTICLES
by
Jeremy Patrick Cain
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MECHANICAL ENGINEERING)
May 2011
Copyright 2011 Jeremy Patrick Cain
Object Description
| Title | Development of a novel heterogeneous kinetics reactor and chemical characterization of soot particles |
| Author | Cain, Jeremy Patrick |
| Author email | jeremycain@me.com; jcain@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Mechanical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2011-02-18 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-03-03 |
| Advisor (committee chair) | Wang, Hai |
| Advisor (committee member) |
Campbell, Charles Phares, Denis Gupta, Malancha |
| Abstract | There is a significant amount of uncertainty in the radiative forcing of black carbon (BC, i.e., soot) on the environment. This is primarily due to its indirect effects (e.g., cloud formation). Several important pieces of information, with regards to particle surface chemistry, are currently unknown and elucidate a complete quantitative assessment: its impact on particle hygroscopicity and cloud condensation (CCN) and ice nuclei (IN) activities, any chemical size dependency and the effects of emission source / fuel, combustion conditions and particle ageing on chemistry. Moreover, heterogeneous processing in the atmosphere is highly dependent upon the surface chemistry and, thus, plays a key role in properly assessing soot’s radiative forcing.; Many previous heterogeneous reaction experiments with soot have inherent reactor design flaws (diffusion) and are conducted at atmospherically peripheral conditions. Thus, a novel reactor, particle–on–substrate stagnation flow reactor, was developed to circumvent these problems. Its design parameters were chosen on the basis of computational fluid dynamics results, and the parameters ensure that all substrate–deposited particles undergoing reaction are subjected to the same diffusive flux. The reaction extent is determined by EDX spectroscopy. Two well–studied heterogeneous reactions were investigated to validate its ability to process particles.; Three different tests for the reaction of NaCl + HNO₃ were investigated first. The reaction rate dependency on surface number density (Ns) for multiple HNO₃ concentrations at a fixed particle size was examined. Second, the uptake coefficient was measured as a function of relative humidity for NaCl, a sea salt–like mixture (NaCl + MgCl₂, Mg/Cl = 0.114) and sea salt. Measurements were also made at one particle size for this series. Lastly, a resistance model was used to reveal rather interesting uptake behavior as a function of particle size. Comparisons with literature values in each case show that the reactor produces quite reasonable results. Cases 1 and 2 were repeated for CaCO₃ + HNO₃. Results were also found to agree reasonably well with the literature.; In addition to the reactor design flaws, a majority of previous heterogeneous reaction studies neither chemically characterize the soot particles under investigation, react the particles in bulk and do not generate or sample particles in a well–controlled manner. Thus, a new technique is implemented: a burner–stabilized, 1–D, laminar, premixed flat flame burner generates soot particles, and a probe sampling system removes the particles from the flame. Particles from the flame are collected in a cascade impactor and analyzed with micro–FTIR spectroscopy. The dependency of aliphatic C–H, C–O and C=O functionalities (relative to aromatic C–H) are quantitatively determined as a function of the maximum flame temperature, particle size and ageing. These groups are currently not accounted for in soot formation models, and are hypothesized to form by persistent free radicals. Moreover, they play a critical role in heterogeneous kinetics, hygroscopicity and CCN and IN activity of soot. Results show that care must be taken in both the generation and sampling processes in order to react chemically similar particles and, thus, remove its contribution to the uptake coefficient uncertainty.; Soot from an aircraft engine was also examined with micro–FTIR spectroscopy. Relative functional group concentrations were measured as a function of particle size and engine power. Analysis of soot from aircraft at various engine powers is needed to determine the surface chemistry of these aerosols produced at airports while taxying and at low, mid and cruise altitudes throughout the flight course. And given that soot from aircraft is not readily available for numerous experimental testing, the feasibility of other readily available generation–sampling systems needs to be assessed so that a proper surrogate may be used to estimate their reactive uptake by various trace gas species. Quantitative comparisons of surface–bound groups are made with samples generated by the flat flame burner operating at different conditions for this purpose. |
| Keyword | soot; heterogeneous kinetics; sea salt; mineral dust; climate change |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3680 |
| Rights | Cain, Jeremy Patrick |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Cain-4379 |
| Archival file | uscthesesreloadpub_Volume23/etd-Cain-4379.pdf |
Description
| Title | Page 1 |
| Full text | DEVELOPMENT OF A NOVEL HETEROGENEOUS KINETICS REACTOR AND CHEMICAL CHARACTERIZATION OF SOOT PARTICLES by Jeremy Patrick Cain A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (MECHANICAL ENGINEERING) May 2011 Copyright 2011 Jeremy Patrick Cain |
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