Dissertation
Measuring Diesel Exhaust Gas Phase Organics with a Thermal Desorption Proton Transfer Reaction Mass Spectrometer
Doctor of Philosophy (PhD), Washington State University
01/2013
Handle:
https://hdl.handle.net/2376/4953
Abstract
Photochemical processing of organic compounds from vehicle emissions forms ozone and increases organic particulate matter concentrations through the formation of secondary organic aerosol (SOA), which is a poorly understood, complex process in urban areas. Recent research has stressed the importance of intermediate volatility organic compounds (IVOCs) in vehicle emissions to SOA formation. A thermal desorption sampling technique was developed and coupled with a Proton Transfer Reaction Mass Spectrometer (PTR-MS) to measure C<sub>10</sub>-C<sub>18</sub> alkanes and other IVOC species. It utilizes an adsorbent resin to collect IVOCs and periodically desorb them into the PTR-MS for measurement. We demonstrated that the PTR-MS is sensitive to alkanes larger than C<sub>9</sub>, which fragment to a common set of ions following a C<sub>n</sub>H<sub>2n+1</sub> (n≥3) pattern. The PTR-MS sensitivity to these alkanes was 1.5 Hz ppbv<super>-1</super>, a factor of 6 lower than toluene, likely due to the proton affinities being less than water. The instrument was used in an urban field experiment and in the laboratory sampling diluted diesel and gasoline engine emissions. Relative to CO<sub>2</sub>, IVOC compound emissions of bicycloalkanes were a factor of 17 and naphthenic monoaromatics were a factor of 3 more abundant in diesel exhaust than in gasoline exhaust. The IVOC alkanes were a factor of 3.5 times more abundance in the diesel exhaust. We calculate the abundance of these IVOC compounds appears to be enough to reconcile the measured to modeled discrepancy related to SOA formation reported from aerosol chamber experiments. The abundance of IVOC alkanes measured in the urban field experiment in Sacramento, CA reached nearly 3 ppbv and was approximately 40% lower on average than the total abundance of benzene and C<sub>1</sub>-C<sub>3</sub> alkylbenzenes which are traditional SOA precursors. The IVOC alkanes were well correlated with soot concentrations (r<super>2</super>>0.95) during two large pollution events. This work indicates that IVOC compound emissions from diesel exhaust may have an important role in urban SOA chemistry.
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Details
- Title
- Measuring Diesel Exhaust Gas Phase Organics with a Thermal Desorption Proton Transfer Reaction Mass Spectrometer
- Creators
- Matthew Howard Erickson
- Contributors
- Tom Jobson (Advisor)Tim VanReken (Committee Member)Heping Liu (Committee Member)Shelley Pressley (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Voiland College of Engineering and Architecture
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 267
- Identifiers
- 99900581848801842
- Language
- English
- Resource Type
- Dissertation