Conferences, Lectures, & Seminars
Events for August
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Environmental Engineering Oral Dissertation Defense
Thu, Aug 01, 2013 @ 03:00 PM - 05:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Nancy Daher, Ph.D. Candidate, USC Astani Department of Civil and Environmental Engineering Graduate Students
Talk Title: Size-Resolved Particulate Matter (PM) in Urban Areas: Toxico-Chemical Characteristics, Sources, Trends and Health Implications
Abstract:
Compelling epidemiological and toxicological evidence indicates consistent associations between exposure to particulate matter (PM) and increased risk of adverse health outcomes. Many of these health effects may result, at least in part, from cellular oxidative stress. However, although an association between PM and health endpoints has been observed, the contribution of specific particle components to aerosol toxicity remains unknown. Most of the evidence is based on mass measures of PM albeit aerosol mass is probably only a surrogate for the real causative particle components. An accurate identification of specific agents of aerosol toxicity, with subsequent targeted emission controls, necessitates an improved characterization of PM composition (chemical and physical), variability (temporal and spatial), sources and their relation to particle oxidative potential.
This dissertation focused on determining the chemical and oxidative properties of size-resolved PM (PM10-2.5, PM2.5, PM2.5-0.25, PM0.25) in distinct urban and roadway environments. Target sites ranged from highly-polluted metropolitans to desert-like locations in the Greater Beirut area, Milan and the Los Angeles basin. PM chemical composition was determined by conducting a chemical mass closure. Specific emphasis was given to the organic and elemental aerosol fractions. PM oxidative potential was quantified using a macrophage-based in vitro reactive oxygen species (ROS) assay. Its association with size-fractionated and chemically-speciated particle components was determined using univariate and multivariate linear regression analyses. The role of water-soluble metals in PM-induced redox activity was particularly investigated. At near-freeway and urban settings in the Greater Beirut area, Mn, Cu, Co, V, Ni and Zn, many of which are air toxics, were mostly distributed in PM2.5-0.25 and PM0.25, with high water-solubility in these modes (> 60%). These physico-chemical characteristics may lead to increased adverse biological effects. Of particular concern were water-soluble metals which strongly correlated with ROS formation. In PM10-2.5, Mn and Co, which are road dust components, were highly associated with ROS-activity. Cu -a tracer of vehicular abrasion-and Co -a road dust element- were potential mediators of PM2.5-0.25-based ROS-activity. In PM0.25, V and Ni, both originating from fuel oil combustion, were strongly correlated with ROS formation. Water-soluble organic carbon was also implicated in PM2.5-induced ROS generation. Moreover, intrinsic (i.e. PM-mass normalized) ROS-activity displayed a particle size-dependency, with lowest activity associated with PM10-2.5. The intrinsic ROS-activity of PM collected from a variety of worldwide urban settings, including Milan, Beirut and Los Angeles, was also quantitatively assessed and compared across areas. Additionally, monthly variation in primary and secondary PM2.5 sources was quantified using the Chemical Mass Balance (CMB) model and fixed tracer-to-OC ratios applied to fine PM collected at a centrally-located urban site in Milan for a year-long period. Spatial variability in quasi-ultrafine PM (PM0.25) in the Los Angeles basin was examined using coefficients of divergence analysis. While PM0.25 mass is relatively spatially homogeneous in the basin, some of its components, mainly elemental carbon, nitrate and several toxic metals, were unevenly distributed, suggesting that population exposure to quasi-ultrafine particles can vary substantially over short spatial scales.
Findings from this work provide additional insight on PM composition, variability, sources and their relation to particle oxidative potential. Advancing our knowledge of PM characteristics that are mostly influential in particle toxicity is essential for establishing more cost-effective and source-specific regulatory strategies for mitigating PM toxicity. Furthermore, an improved understanding of the spatial and temporal complexities of hazardous particle components provides guidance for more carefully-targeted epidemiological studies for personal exposure assessment.
Advisor: Prof. Costas Sioutas
Host: Nancy Daher
Location: Kaprielian Hall (KAP) - 209 Conference Room
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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CEE Oral Dissertation Defense
Wed, Aug 14, 2013 @ 10:00 AM - 12:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Ziyi Huang, Ph.D. Candidate, Astani Departmentof Civil and Environmental Engineering, USC
Talk Title: OPEN CHANNEL FLOW INSTABILITIES: MODELING THE SPATIAL EVOLUTION OF ROLL WAVES
Abstract:
This study is concerned with "roll waves", which are a series of intermittent shock-like waves occurring in turbulent water flows down a wide, rectangular open channel due to the natural instability. Most literatures on the subject of roll waves have concentrated on theoretical investigations. Only two of them made efforts on computationally simulating real roll-wave flows, but no validation tests were implemented.
A computational model capable of simulating the spatial evolution of roll waves is constructed in the present work. The equations of motion are the one-dimensional viscous Saint Venant equations, incorporating the turbulently viscous force to describe the momentum diffusion resulting from tremendous gradient and curvature of roll waves. The equations are solved by a high-resolution, shock-capturing numerical scheme. The scheme is based on the conservative finite volume formulation and adopts the second-order TVD Lax-Wendroff Riemann solver. The computational model, written in FORTRAN 95, is named as "Shallow Water Analyzed by a TVD Scheme at University of Southern California'' with an acronym "USC SWAT''. It can be applied to analyze a wide range of shallow water flows.
The numerical scheme is tested through comparisons with both transient linear and quasi-steady nonlinear theories. The numerical solutions of maximum amplitude of progressing roll waves match the linear theory at time levels in which the wave amplitude is small. The numerical solution of converged progressing roll waves match a mathematical solution of roll waves deduced from the governing equations in a progressing coordinate.
The constructed computational model is utilized to simulate real roll-wave flows in a constant-slope channel. In the validation test, the spatial development curves of time-averaged wave crest and trough depths achieved from the simulation are compared with those from experimental data. It is shown that the value of the turbulent viscosity needs to be appropriately selected so as to agree with the experimental data. The comparison results manifest the simulation satisfactorily predicts the spatial evolution of wave crest and trough depths.
Some of important roll-wave properties are investigated. The simulation discovers three types of wave-wave interactions, which impact characteristics of the roll-wave evolution. The spatial evolution of roll waves obeys a generality despite different hydraulic conditions. The nonperiodicity of roll waves increases from upstream to downstream channel locations.
The extent of the flow instability is weakened in channels with rough bottom. A concept of the breaking-slope open channel is tested through a computational experiment. This concept is found to be useful in suppressing growth of the roll-wave amplitude.
This computational study covering the comparison with experimental data enriches the knowledge of computational mechanics regarding free-surface water flows, and provides a complete insight on simulating the spatial evolution of roll waves using the Saint Venant equations. Findings from the computational experiments on mitigating the roll-wave evolution could help overcome difficulties caused by open channel flow instabilities.
Advisor: Prof. J.J. Lee
Location: Kaprielian Hall (KAP) - 209 Conference Room
Audiences: Everyone Is Invited
Contact: Evangeline Reyes