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ULTRAFINE PARTICLE CONCENTRATION INSIDE VEHICLES:
MODELS FOR EXPOSURE ASSESSMENT
by
Neelakshi Hudda
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 (ENVIRONMENTAL ENGINEERING)
August 2012
Copyright 2012 Neelakshi Hudda
Object Description
| Title | Ultrafine particle concentration inside vehicles: models for exposure assessment |
| Author | Hudda, Neelakshi |
| Author email | hudda@usc.edu;neelakshi.hudda@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Environmental Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2012-05-23 |
| Date submitted | 2012-07-15 |
| Date approved | 2012-07-16 |
| Restricted until | 2012-07-16 |
| Date published | 2012-07-16 |
| Advisor (committee chair) | Sioutas, Constantinos |
| Advisor (committee member) |
Henry, Ronald Phares, Dennis Fruin, Scott |
| Abstract | Despite the proven toxicity of ultrafine particles (UFP), epidemiological studies focusing on them are rare. This is at least in part because accurate exposure assessment for such studies is challenging due to the ubiquitous and dynamic nature of UFP, and successful epidemiological studies will depend on the ability to characterize personal exposure in several key microenvironments. The in-vehicle or in- transit microenvironment is one such microenvironment. This is because for large sections of the population, highest UFP concentrations are often encountered during travel, i.e., where close proximity to relatively undiluted vehicular emissions occurs. ❧ This thesis focuses on developing useful models for linking roadway UFP concentrations to in-vehicle concentrations. Even when roadway concentrations are known, correct assignment of exposure requires an additional parameter, the inside-to-outside UFP ratio (I/O), which reflects the combined effects of multiple mechanisms that either limit the pollutant penetration inside vehicles or cause loss therein. I/O ratios can vary from nearly zero to one, within an individual vehicle, depending on the ventilation condition, fan setting and speed. It also varies widely within a vehicle fleet due to differences in vehicle age, model and manufacturer. However, it is not feasible to measure I/O ratios for thousands of individual vehicles, as is required in large epidemiological studies, hence the need for accurate predictive models. ❧ Results from a test fleet representative of the U.S. fleet in terms of age, mileage, volume and manufacturer distribution, suggest that UFP I/O ratio is strongly dependent on air exchange rate (AER) of the vehicle, which in turn is determined by ventilation mode, ventilation fan setting, driving speed, cabin volume and age of the vehicle. The UFP I/O ratios measured under recirculation (RC) ventilation mode were far lower than those under outside air intake (OA) conditions due to typically an order of magnitude lower AERs under RC mode than under OA mode. Predictive models developed for AER and I/O ratios were able to account over 70% of variation in measured data. All the predictive variable values are easily obtainable through questionnaire, which will be useful to exposure and epidemiological studies. ❧ As a demonstration of model usefulness and scalability to dynamic real world scenarios, UFP I/O ratio distributions were further linked to UFP concentrations measured on-road on multiple routes (freeways and arterial roads) in Los Angeles. In-vehicle concentrations varied by over a magnitude due to inter-vehicle variability and ventilation choice (windows open, RC or OA), and inter-vehicle variation in I/O ratios was often larger than the variability in on-road concentrations. In general, exposure concentration increased two to four fold when ventilation mode was switched from RC to OA. In a real-world setting, 1) ventilation setting, 2) roadway type (arterial or freeway) and 3) the totality of vehicle and driving characteristics (age, manufacturer and speed) each are all of roughly similar impact on in-vehicle UFP concentration. ❧ The research described in this thesis demonstrates that the in-vehicle microenvironment is unique in its extreme variability, but that in-vehicle UFP concentrations are predictable based on easily obtainable information. Furthermore, the key physical mechanism determining in-vehicle concentrations is AER, which too is predictable. Therefore, determining UFP exposures in vehicles, previously a difficulty and key gap in UFP exposure assessment, is now possible. The work can also serve as a basis for other particulate pollutants and reactive gaseous species in in-vehicle and other indoor environments. |
| Keyword | air exchange rate; exposure model; in-vehicle; microenvironment; roadway exposure; ultrafine particle |
| 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-m |
| Rights | Hudda, Neelakshi |
| Access conditions | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@usc.edu |
| Archival file | uscthesesreloadpub_Volume4/etd-HuddaNeela-956.pdf |
Description
| Title | Page 1 |
| Full text | ULTRAFINE PARTICLE CONCENTRATION INSIDE VEHICLES: MODELS FOR EXPOSURE ASSESSMENT by Neelakshi Hudda 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 (ENVIRONMENTAL ENGINEERING) August 2012 Copyright 2012 Neelakshi Hudda |
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