The Origin and Nature of Persistent Combustion-Generated Radicals

这项工作的目标是确定在什么燃料和什么条件下，在燃烧系统中形成持久自由基，并最终纳入空气中的细颗粒物（PM2.5）。具体目标包括：1。实验确定已知的半醌自由基前体在火焰后燃烧条件下如何反应以及在何种条件下形成自由基。采用高温流动反应器/气相色谱仪/质谱仪系统研究对苯二酚和儿茶酚在氧化和热解条件下的热反应。利用低温技术捕获废水，通过电子顺磁共振（EPR）进行分析。2. 实验确定各种常用燃料产生稳定自由基的燃烧条件。实验室反应器用于研究各种燃料的热降解和捕获自由基进行表征。候选燃料包括：丙烷、汽油、柴油、生物柴油、6号燃料油、煤、木材和氯化烃混合物。确定哪些前体和颗粒表面形成并稳定持久自由基。采用填充床反应器系统，用半醌型自由基前体给药替代粒子样品，研究了化学吸附自由基假说。所研究的颗粒包括掺杂铁、铜、镁、钙或锌的活性炭和二氧化硅或氧化铝。研究的自由基前体包括对苯二酚、儿茶酚、酚类、苯和氯化类似物。测定含碳物质是否形成持久的自由基。本然自由基假说是通过产生和修饰燃料热降解形成的烟灰或炭来研究的。在不同氧化剂（O2, NO2， OH， O和Cl）部分氧化前后，将对颗粒进行自由基表征。自由基浓度和寿命由epr测定。利用从头算方法研究半醌类自由基的结构、稳定性和反应性。密度泛函理论（DFT）程序被用来计算从对苯二酚和儿茶酚衍生的自由基的结构、能量和自旋密度，以及在实验任务中确定的相关自由基。6. 为了证明类似的持久性自由基是否与全尺寸燃烧衍生和环境PM2.5样本有关。对有限数量的全尺寸燃烧和空气中PM2.5样本进行了表征，以量化相关的自由基和可能在稳定它们方面起作用的金属（铁、铜、镁、钙、锌）。持久的、燃烧产生的自由基的概念是一个需要探索性研究的领域，以确定这些自由基的性质、来源和在各种条件下的反应性。该项目旨在提供这些信息，以便研究界能够进一步探索持久性自由基在特定条件下和特定应用中的影响。它还支持与博士的持续合作。路易斯安那州立大学生物动力学研究所的William A. Pryor和Guiseppe Squadrito以及路易斯安那州立大学和杜兰医学院的其他健康影响研究人员。本研究结果为深入研究持久性自由基的生物化学和健康影响奠定了基础。

PROJECT SUMMARYThe goal of this work is to determine from what fuels and under what conditions persistent radicals are formed in combustion systems and ultimately incorporated into airborne fine particulate matter (PM2.5). Specific objectives include:1. To determine experimentally how known semiquinone radical precursors react under post-flame combustion conditions and under which conditions they form radicals. This is done using a high-temperature flow reactor/gas chromatograph/mass spectrometer system to study the thermal reactions of hydroquinone and catechol under oxidative and pyrolytic conditions. Effluent is trapped using cryogenic techniques for analyses by electron paramagnetic resonance (EPR). 2. To determine experimentally the combustion conditions under which various common fuels generate stable free radicals. Laboratory reactors are used to study the thermal degradation of various fuels and to trap free radicals for characterization. Candidate fuels include: propane, gasoline, diesel fuel, biodiesel fuel, No. 6 fuel oil, coal, wood, and a chlorinated hydrocarbon mixture.3. To identify which precursors and particle surfaces form and stabilize persistent free radicals. The chemisorbed radical hypothesis is investigated by dosing surrogate particle samples with semiquinone-type radical precursors using a packed-bed reactor system. The particles investigated include activated carbon and silica or alumina doped with iron, copper, magnesium, calcium or zinc. Radical precursors studied include hydroquinone, catechol, phenols, benzenes, and chlorinated analogues..4. To determine if carbonaceous materials form persistent free radicals. The intrinsic radical hypothesis is investigated by generating and modifying soots or chars formed by thermal degradation of fuels. The particles will be characterized for radicals before and after partial oxidation with various oxidants (O2, NO2, OH, O, and Cl). The radical concentrations and lifetimes are determined by EPR.5. To elucidate the structure, stability, and reactivity of semiquinone-type radicals using ab-initio calculation techniques. Density function theory (DFT) procedures are used to calculate the structures, energies, and spin densities of radicals derived from hydroquinone and catechol as well as related radicals identified in the experimental tasks. 6. To demonstrate whether similar persistent radicals are associated with full-scale combustion-derived and ambient PM2.5 samples. A limited number of full-scale combustion and airborne PM2.5 samples are characterized to quantify associated radicals and the metals (iron, copper, magnesium, calcium, zinc) that may have a role in stabilizing them. Broader Impacts The concept of persistent, combustion-generated free radicals is an area that needs exploratory research to establish the nature, origin, and reactivity of these radicals under a variety of conditions. This project is designed to provide this information so that the research community can further explore the impact of persistent radicals under specific conditions and for specific applications. It also supports an ongoing collaboration with Drs. William A. Pryor and Guiseppe Squadrito of the Biodynamics Institute at LSU and other health-effects researchers at LSU andTulane Medical School. The results of this study form a basis for detailed studies of the biological chemistry and health impacts of persistent free radicals.