Events Calendar

Environmental Engineering Oral Dissertation Defense

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