Photochemical Transformations of Pollutants: Nitropyrene

1-硝基芘（1-Nitropyrene）是一种具有致突变性和高度致癌性的多环芳烃（PAH），是柴油机尾气中含量最多的硝化PAH，也存在于燃煤飞灰、熟肉制品和煤油加热器的排放物中。在城市和郊区的空气中发现的浓度在皮克/立方米范围内，因此人类有可能通过吸入接触。这些无处不在的污染物在大气中的转化仍然存在争议， 硝基多环芳烃的命运是通过颗粒物质的光分解。虽然在溶液研究中已经确定了一些光降解速率和产物，但没有活性中间体被表征以支持所提出的机制。类似的研究，这些分子吸附在基板上，这类似于他们的环境中的状态，已经受到了更多的限制。 在这项工作中，我们建议利用技术，我们已经在我们的实验室开发，研究吸收到大气气溶胶模型的硝基芘的光化学转化机制，以提供一些了解这些污染物在大气中的命运。正如我们在多环芳烃中发现的那样，固体/空气界面的光转化可以对控制其在环境中的停留时间产生重大影响，因此对于评估这些污染物的潜在风险以及可能的设计非常重要。系统去除。为了更好地理解吸附态硝基芘的光转化机理，我们将：（1）通过吸收和荧光技术研究吸附态分子与不同底物的相互作用，并确定参与的激发态的性质;（2）测定相对光降解速率;（3）通过时间分辨确定中间物种和三重态 漫反射激光光谱和电子自旋共振和（4）鉴定稳定产物并将它们与在溶液光化学中发现的那些进行比较。本建议的一个基本目的是研究的一些化学和物理性质的吸附剂，如组合物，水含量，共吸附气体的存在下，平均孔径和表面覆盖度上的吸附的硝基芘的物理和光化学过程的影响。此外，从模拟气溶胶的极性和非极性溶剂中的激光照射产生的激发态和活性中间体的特征在于激光闪光瞬态光谱。这最后一个目标的实现是最重要的，因为硝基多环芳烃也可以在燃烧气溶胶的有机液体样核心中发现。

1-Nitropyrene, a well known mutagenic and highly possible carcinogenic polycyclic aromatic hydrocarbon (PAH), is the most abundant nitrated PAH emitted in diesel engine exhaust and also found in coal combustion fly ash, cooked meat products and kerosene heaters emissions. It has been found at concentrations in the pg/m3 range in the air over urban and suburban areas and thus it has potential for human exposure through inhalation. The transformations in the atmosphere of these ubiquitous pollutants is still debated and a possible environmental fate for nitroPAHs is through their photodecomposition on particulate matter. Although some photodegradation rates and products have been determined in solution studies no reactive intermediates have been characterized to support the proposed mechanisms. Similar studies on these molecules adsorbed on substrates, which resemble their state on the environment, have been much more limited. In this work we are proposing to utilize techniques, we have already developed in our laboratory, to study the photochemical transformation mechanisms of nitropyrenes adsorbed into models of atmospheric aerosols in order to provide some understanding of the fate of these contaminants in the atmosphere. As we have found with PAHs, 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. In order to understand the phototransformation mechanism of adsorbed nitropyrenes we will: (1) examine the interactions of the adsorbed molecules with the different substrates and establish the nature of the participating excited states by absorption and fluorescence techniques, (2) determine relative photodegradation rates, (3) identify intermediate species and triplet states by time resolved diffuse reflectance laser spectroscopy and electron spin resonance and (4) identify the stable products and compare them with those found in the solution photochemistry. A fundamental aim of this proposal is to study the effect of some chemical and physical properties of the adsorbent such as composition, water content, presence of coadsorbed gases, average pore diameter and surface coverage on the photophysical and photochemical processes of the adsorbed nitropyrenes. Also, the resulting excited states and reactive intermediates from the laser irradiation in polar and non polar solvents that mimic the aerosol will be characterized by laser flash transient spectroscopy. The accomplishment of this last aim is of most importance since nitroPAHs can be also found in the organic liquid like-core of combustion aerosols.