Theses and Dissertations from UMD
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Item Experimental Investigations and Scaling Analyses of Whirling Flames(2020) Hariharan, Sriram Bharath; Gollner, Michael J; Oran, Elaine S; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Swirling flows are ubiquitous in nature, occurring over a large range of length scales -- on the order of many tens-of-thousands of kilometers in the case of Saturn's hexagonal polar vortex, to just a few centimeters in dandelion flight. Most instances of swirling flow involve momenta competing in two different directions, axial and azimuthal. Whirling flames (also known as fire whirls) occur at the intersection of vortical flow fields and buoyant, reactive plumes, and they represent a general class of flows that may be considered slender vortices involving axial momentum from heat-release and tangential momentum from air entrainment. In this work, two previously unexplored characteristics of whirling flames are considered over a wide range of scales, spanning three orders of magnitude in length and four orders in heat-release rate. First, emissions of particulate matter (PM) from fire whirls (FW) were measured and compared to those from free-buoyant pool fires (PF). For different pool diameters and fuels, FWs showed higher burning rate and fuel-consumption efficiency, but lower PM-emission rate, leading to lower PM-emission factors. The lower PM emissions from FWs is attributed to a feedback cycle between higher oxygen consumption from improved entrainment, higher average temperatures, increased heat feedback to the fuel pool, which in turn increases burning rate and entrainment. A scaling analysis showed that the PM emission factor decreased linearly with the ratio of inverse Rossby number to nondimensional heat-release rate. Second, the structure of the blue whirl (BW), a soot-free regime, was investigated using dimensional analysis and non-intrusive optical diagnostics. Experimental data of heat-release rates and circulation for BWs and FWs from the literature were used to define the nondimensional equivalents of buoyant and azimuthal momenta. The combinations of these parameters showed that FWs primarily formed in a buoyancy-dominated regime, and that a circulation-dominated regime was required for BW formation, corroborating hypotheses that the transition was caused by the bubble mode of vortex breakdown, resulting in the formation of a recirculation zone. Finally, OH- and PAH-PLIF, OH* and CH* chemiluminescence suggest a triple-flame structure anchored at the blue ring region of the BW, with the rich branch formed by the lower blue cone, and the lean branch by the upper purple haze. These results show that the mixing process occurs upstream of the conical region and that the recirculation zone is comprised of combustion products.Item Relationships of social and physical environmental factors with cardiometabolic outcomes(2019) Huang, Dina; Puett, Robin; Nguyen, Quynh C; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The social and physical environmental factors impact health in general and have been linked with increased risks of cardiometabolic outcomes including obesity, diabetes, hypertension and cardiometabolic biomarkers. The dissertation added to important knowledge on this topic in two ways: 1) by leveraging innovative Twitter-derived characteristics to study the potential influence of social environment on cardiometabolic outcomes, 2) investigating the effects of air pollution exposures on cardiometabolic outcomes in youth living with type I diabetes. The first study investigated the associations between Twitter-derived area-level predictors (happiness, diet, physical activity) with cardiometabolic outcomes (obesity, diabetes, hypertension) using a nationally representative sample from National Health and Nutrition Examination Survey (NHANES). People living in neighborhoods with higher happiness, healthier diet and more physical activity had lower prevalence of obesity and hypertension but not diabetes. Twitter-derived social neighborhood characteristics can be used to identify communities with higher risk of cardiometabolic outcomes. We obtained data from SEARCH for Diabetes in Youth (SEARCH) study for the second and the third study. The second study examined the associations between chronic exposure to air pollution and glucose hemostasis (HbA1c) in youth living with type I diabetes. Particulate matter with aerodynamic diameter <2.5 (PM2.5), proximity to heavily trafficked roads and annual average daily traffic count were associated with higher HbA1c in study site South Carolina, Colorado and Washington, but not in study site Ohio and California. Differences in particulate matter compositions may explain the inconsistent results. The third study assessed the effect of acute exposure to air pollution on subclinical CVD markers including pulse wave velocity (PWV), augmentation index (AIx) and brachial distensibility (BrachD) using a repeated measures design. Reduction in PM2.5 on the day prior to assessment was associated with lower AIx, but not associated with either PWV or BrachD. In summary, exposure to air pollution may be associated with cardiometabolic outcomes and reducing air pollution may have implications in early prevention of cardiovascular complications for youth living with type I diabetes. Overall, reducing social stressors and reducing hazardous physical environmental factors may decrease the risk of cardiometabolic outcomes, providing possible directions for CVD prevention for public health practitioners.Item AIR QUALITY ASSESSMENT OF RESIDENTIAL EXPOSURE TO PARTICULATE MATTER AND VOLATILE ORGANIC COMPOUNDS NEAR A CONCRETE BLOCK PLANT AND TRAFFIC IN BLADENSBURG, MARYLAND(2018) Ezeugoh, Rosemary Ifeoma; Wilson, Sacoby M; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ambient air pollution from stationary sources, industrial traffic, and commuter traffic can negatively impact air quality and human health. Ernest Maier, a concrete block plant located in Bladensburg, Maryland wants to expand to include a concrete batching plant on the same property. This expansion could further degrade air quality and impact the health of vulnerable residents. Air quality monitoring were conducted in the community at five personal sites using the Airbeam and Atmotube, which are wearable, real-time sensors that can measure PM2.5 and VOCs respectively. Sampling and traffic counts were conducted in thirty minutes’ periods to capture morning on-peak, afternoon off-peak and evening on-peak periods. Pearson’s correlation revealed that a weak correlation among the PM2.5 and VOC concentrations observed between the different sites and some of the values were found to be statistically significant. ANOVA analysis showed that the PM2.5 levels were significantly different at the different sites (p-value 0.001).Item ASSESSING THE EFFECTIVENESS OF VEGETATIVE ENVIRONMENTAL BUFFERS IN MITIGATING POULTRY-EMITTED AIR POLLUTANTS(2017) Yao, Qi; Torrents, Alba; Hapeman, Cathleen J.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The noticeable expansion of the concentrated feeding operation in the poultry industry has been putting considerable stress on the atmospheric environment and is also a public health concern. Poultry manure has been widely identified as a potential water pollutant source by regulators and researchers. However, less is known about the atmospheric emissions from poultry houses which includes particulate matter (PM), ammonia, and volatile organic compounds (VOCs). Vegetative Environmental Buffers (VEBs) have been introduced as a possible air pollutant migration technology to poultry farms. VEBs are vegetation designed to serve as a visual screen and consist of trees, shrubs, grass and other plants. Preliminary studies suggested that VEBs are able to reduce air pollutant emissions, however quantitative studies are needed to improve the overall design and assess their effectiveness. In this project, field experiments at three different poultry houses were conducted to quantify the efficacy of VEBs in migrating air pollutants. Time-integrated particulate, ammonia, and air samples were collected at multiple locations and heights. A small-scale Gaussian plume model was used to predict pollutant emissions from a poultry house without a VEB under the same meteorological conditions. Results showed significant TSP, PM10, PM2.5, and NH3 concentration decreases behind the VEB. Methanol, acetone, and ethanol were the most abundant VOCs emitted from the poultry house, but these compounds can also can contribute to the formation of ground level ozone. VEBs were showed promising potential in decreasing the ozone formation potential of VOCs. This project will contribute to the National Conservative Practice Standard (NCPS # 380 or # 420) by providing important expertise to the design and proper installation of VEBs. The work has been presented in extension and outreach programs.Item ASSOCIATIONS BETWEEN AMBIENT PARTICULATE MATTER EXPOSURES, STROKE, AND MARKERS OF CARDIOVASCULAR INFLAMMATION(2017) Fisher, Jared A.; Puett, Robin C; Epidemiology and Biostatistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stroke is a leading cause of morbidity and mortality in the United States with 795,000 people experiencing a new or recurrent stroke every year. Identifying modifiable risk factors for stroke should therefore be considered a research priority. While associations between ambient exposure to air pollution and other cardiovascular diseases are well established in the literature, the evidence linking particulate matter (PM) air pollution exposures to the risk of ischemic or hemorrhagic stroke remains equivocal. Furthermore, the exact pathophysiologic mechanisms by which exposure to PM may lead to cerebrovascular events are not yet fully understood. Hypothesized pathways include the mediation of effects through a combination of inflammatory responses, autonomic dysregulation, and/or vascular endothelial disturbances. This dissertation addresses existing gaps in the literature in three separate studies. Two time-stratified case-crossover studies examined the association between short-term PM exposures and stroke risk, one in the Health Professionals Follow-up Study (HPFS) and the other among a large database of Maryland stroke hospitalizations. Conditional logistic regression models were used to examine associations by stroke subtype, population subgroups, and clinically-relevant variables. Our third study took place within the Nurses’ Health Study cohort. Multivariable linear regression models were used to examine the associations between PM and residential distance to road exposures and four inflammatory biomarkers (CRP, IL-6, fibrinogen, and ICAM-1). We found positive significant associations between PM10 and ischemic stroke events in the HPFS cohort, and associations were elevated for nonsmokers, aspirin nonusers, and those without a history of high cholesterol. Concentrations were elevated for both CRP and IL-6 among participants who lived close to a major roadway, but no significant results were found by estimated PM exposure. This work provides additional evidence that PM exposure is associated with ischemic stroke and adds to the current literature that those not currently taking aspirin and those without a history of high cholesterol may be at elevated risk. Although the direct role of inflammatory processes requires more investigation, this work does provide additional evidence that proximity to traffic may influence cardiovascular-related inflammation.Item Development, enhancement, and evaluation of aircraft measurement techniques for criteria pollutants(2014) Brent, Lacey Cluff; Dickerson, Russell R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The atmospheric contaminants most harmful to human health are designated Criteria Pollutants. To help Maryland attain the national ambient air quality standards (NAAQS) for Criteria Pollutants, and to improve our fundamental understanding of atmospheric chemistry, I conducted aircraft measurements in the Regional Atmospheric Measurement Modeling Prediction Program (RAMMPP). These data are used to evaluate model simulations and satellite observations. I developed techniques for improving airborne observation of two NAAQS pollutants, particulate matter (PM) and nitrogen dioxide (NO2). While structure and composition of organic aerosol are important for understanding PM formation, the molecular speciation of organic ambient aerosol remains largely unknown. The spatial distribution of reactive nitrogen is likewise poorly constrained. To examine water-soluble organic aerosol (WSOA) during an air pollution episode, I designed and implemented a shrouded aerosol inlet system to collect PM onto quartz fiber filters from a Cessna 402 research aircraft. Inlet evaluation conducted during a side-by-side flight with the NASA P3 demonstrated agreement to within 30%. An ion chromatographic mass spectrometric method developed using the NIST Standard Reference Material (SRM) 1649b Urban Dust, as a surrogate material resulted in acidic class separation and resolution of at least 34 organic acids; detection limits approach pg/g concentrations. Analysis of aircraft filter samples resulted in detection of 8 inorganic species and 16 organic acids of which 12 were quantified. Aged, re-circulated metropolitan air showed a greater number of dicarboxylic acids compared to air recently transported from the west. While the NAAQS for NO2 is rarely exceeded, it is a precursor molecule for ozone, America's most recalcitrant pollutant. Using cavity ringdown spectroscopy employing a light emitting diode (LED), I measured vertical profiles of NO¬2 (surface to 2.5 km) west (upwind) of the Baltimore/Washington, area in the morning, and east (downwind) in the afternoon. Column contents (altitude integrals of concentration) were remarkably similar (≈3x1015 molecules cm−2). These measurements indicate that NO2 is widely distributed over the eastern US and help quantify the regional nature of smog events and prove extensive interstate transport of pollutants. These results were used to help shape air pollution control policy based on solid science.Item CHARACTERIZATION OF CARBONACEOUS AEROSOL: IMPROVED METHODS, SOURCES AND SIZE DISTRIBUTIONS(2006-11-30) Crimmins, Bernard Shawn; Baker, Joel E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A highly sensitive method was developed for measuring polycyclic aromatic hydrocarbons and nitro-substituted polycyclic aromatic hydrocarbons in ambient aerosol. Using large volume injection, this technique provided an order of magnitude increase in sensitivity compare to conventional injection techniques. This method facilitated the measurement of the first reported diurnal size distribution of NPAHs. Size resolved samples were collected using a Berner low-pressure impactor deployed at the Baltimore PM2.5 Supersite in April 2002. Both classes of compounds were found predominantly on particles less than 0.49μm with similar size distributions among samples for most of the 12 hr periods. A linear relationship between compound geometric mass median aerodynamic diameter (GMMAD) and log sub-cooled vapor pressures (pl°) was observed for PAHs and NPAHs, respectively, during each sampling period. The inter-relationhips between the slopes and y-intercepts from the GMMAD/log vapor pressure correlations suggest the source of PAHs to the Baltimore atmosphere reside on particles with GMMADs equal to 0.18 μm, consistent with vehicle emissions. Bulk organic aerosol was collected in Baltimore, MD during the spring, summer and winter of 2002-2003. Concentrations of n-alkanes, hopanes, polycyclic aromatic hydrocarbons (PAH), and nitro-substituted polycyclic aromatic hydrocarbons (NPAH) were measured in the gas and particle phase. The organic compounds varied little, with seasonal concentrations typical of North American urban atmospheres. Principal Components Analysis/Multiple Linear Regression (PCA/MLR) and Positive Matrix Factorization (PMF) were used to determine the sources of individual compound classes (PAHs, NPAHs, hopanes and alkanes) and total particulate carbon and PM2.5 to the Baltimore atmosphere for during 2002-2003. PMF was used to determine the total carbon and PM2.5 source estimates to the Baltimore atmosphere. The sources identified included tire wear/road dust, gasoline and diesel exhaust, oil combustion, biogenic, secondary organic aerosol, incineration, and coal explaining 64% of the variability in the total carbon and PM2.5 concentrations.