Microstructural Pathway of EPFR Formation and their Decay Mechanisms

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Project Summary/Abstract: Project 5 There is strong evidence that environmentally persistent free radicals (EPFRs) associated with partic- ulate matter (PM) and soils found in/around declared and potential Superfund sites pose adverse health effects. Mitigation of the associated environmental risks requires a detailed understanding of EPFR-contaminated air and soil systems. Specifically, Project 5 is in direct alignment with SRP Man- date 4, which is elucidating chemical and physical methods to reduce the amount and toxicity of these hazardous substances. Project 5 will study the microscopic, or atomistic, properties of EPFR for- mation, including their remarkable stability in the environment, and will model the resulting influences of chemical decay on a broad base of metal oxide (MO) platforms. Employing a toolbox of state-of- the-art experimental and molecular ab initio computational methods across differing material plat- forms (surfaces, nanoclusters/powders, clays, EPA fly ash, soil), our continued focus is on elucidating individual details of and corresponding local effects (electronic/chemical/atomic structure) on organic molecular-metal oxide/center chemisorption, ensuing charge transfer (redox), and consequent chemi- cal degradation pertinent to EPFR-containing systems such as PM, powders, clays, and real-world (field EPFR) materials. Our Aims focus on answering three simple questions at an atomistic level: 1) How do EPFRs chemically form? 2) What causes EPFR decay? and 3) Why are EPFR properties simi- lar across differing platforms? While our previous efforts have elucidated trends in EPFR formation, the connection between EPFR decay mechanisms, lifetimes, and dependence on MO—the path to destabilization/remediation (SRP Mandate 4)—has not yet been addressed and is a main goal of our project. Although focused primarily on revealing fundamental environmental science, our Project will work symbiotically with the Center. By identifying material factors from our other SRP Projects and correlating results across differing material platforms, we will obtain synergistic/antagonistic tendency parameters for EPFR destabilization/remediation that translate to other Projects, and in turn, initiate and clarify mitigation and remediation strategies. By employing experimental processes that both model and recapitulate real world exposures, Project 5 will provide a picture of the microscopic sys- tems generating the EPFRs and related adsorbate systems, but more importantly, will interrogate ef- fects that promote/hinder degradation and the corresponding products that influence and enhance activities across the Center (Projects 1–4 and all the Cores). Integrating closely with and expanded by Project 4, this will allow our Center to synergistically elucidate the atomic mechanisms of the EPFR chemistry in a scalable and predictive manner that contributes to understanding biochemical health effects, mitigation, and remediation of these particle-bound pollutants at Superfund sites.