Photodegradation Reactions Mono and Dinitro PAHs

描述（由申请人提供）：颗粒物（PM2.5）与一系列严重的呼吸和心血管健康问题有关。在PM2.5中发现的硝基多环芳烃是在燃烧过程中或由污染大气中多环芳烃的化学或光化学反应形成的。硝基多环芳烃已在城市污染空气中收集的可吸入颗粒物、柴油尾气颗粒、汽车尾气、煤飞灰和木材烟雾的提取物中被鉴定出来。硝基多环芳烃在环境空气中的含量通常低于多环芳烃，其浓度范围为pg/m3至ng/m3。尽管如此，在实验室生物测定中，它们中的一些可能比母体多环芳烃更具诱变性或致癌性。因此，了解它们在大气中的来源和转化，对评估环境暴露和风险具有重要意义。具体来说，它们在固体/空气界面或燃烧产生的气溶胶的有机部分的液体环境中的转化可以对控制它们在环境中的停留时间产生重大影响。研究这两种环境下的光化学是很重要的，因为它们的光降解可以通过完全不同的机制进行，这取决于反应介质。

DESCRIPTION (provided by applicant): Particulate matter (PM2.5) has been linked to a range of serious respiratory and cardiovascular health problems. The nitroPAHs found in the (PM2.5) are formed during combustion processes or by either chemical or photochemical reactions of polycyclic aromatic hydrocarbon in polluted atmospheres. NitroPAHs have been identified in extracts of respirable particles collected from polluted urban air, diesel exhaust particles, automobile exhaust, coal fly ash and wood smoke. The nitroPAHs are typically less abundant in ambient air than PAHs and are found at concentrations in the range of pg/m3 to ng/m3. Nonetheless, some of them could be more mutagenic or carcinogenic in laboratory bioassays than the parent PAH. Thus, it is of great significance to understand their sources and transformations in the atmosphere in assessing environmental exposure and risks. Specifically, their transformations at the solid/air interface or in the liquid-like environment of the organic fraction of the combustion derived aerosols can have a significant impact on controlling their residence time in the environment. It is important to study the photochemistry in these two environments because their photodegradation can proceed by entirely different mechanisms depending on the reaction medium. We are proposing to utilize techniques, already developed in our laboratory, to study the photochemical transformation mechanisms of nitroPAHs adsorbed or absorbed into models of atmospheric particulate matter in order to provide some understanding of the fate of these contaminants in the atmosphere. As we have found with PAHs, that phototransformations at the solid/air interface can have a significant impact in controlling their residence time in the environment, and are thus important in the evaluation of the potential risks of these contaminants, as well as in the possible design of systems for their removal. The working hypothesis is that the physical and chemical properties of the particulate matter are determining factors in the reactivity of the excited states and intermediates participating in the photochemical transformations of these pollutants in that environment. In order to understand the phototransformation mechanism of adsorbed or absorbed nitroPAHs we will: (1) isolate/and characterize the principal stable photoproducts and determine their quantum yields and the effect of the nature of the solvent (polar, non polar, polar aprotic, hydrogen abstraction easiness), and of organic compounds found in the atmospheric aerosols on the product yields, (2) isolate and characterize the principal stable photoproducts produced on adsorbents that mimic the atmospheric particle matter such as inorganic oxides, and sulfate salts, and determine the effect of the physical and chemical properties of the surfaces of these solids (such as composition average pore diameter, surface coverage) on the products relative yields, and to compare their relative yields and distribution with those obtained in the different solvents. The effect of coadsorbed water and oxygen on the yields will also be examined and (3) identify and characterize the participating excited states and reactive intermediates in the phototransformation process occurring in solution and on the surfaces. Related to this aim is the determination of the effect of organic cosolutes encountered in the atmospheric aerosol on the reaction kinetics of the intermediates. The physical properties of the participating excited states and reactive intermediates will be supported by quantum mechanical calculations.