Photochemical Transformations of Pollutants: Nitropyrene

1-硝基吡喃是一种已知的致癌多环芳烃(PAH)，是柴油机排气中含量最高的硝化多环芳烃，也存在于燃煤飞灰、熟肉制品和煤油加热器的排放中。已在城市和郊区的空气中发现其浓度在pg/m~3范围内，因此有可能通过吸入使人接触到这种物质。这些无处不在的污染物在大气中的变化仍然存在争议，可能的环境问题 硝基多环芳烃的命运是通过它们在颗粒物上的光解来实现的。虽然在溶液研究中已经确定了一些光降解速率和产物，但还没有活性中间体的特征来支持所提出的机理。对于吸附在底物上的这些分子的类似研究，就像它们在环境中的状态一样，要有限得多。 在这项工作中，我们建议利用我们实验室已经开发的技术，研究吸附到大气气溶胶模型中的硝基吡喃的光化学转化机理，以便对这些污染物在大气中的去向提供一些了解。正如我们在多环芳烃中发现的那样，固体/空气界面上的光转化可以对控制它们在环境中的停留时间产生重大影响，因此在评估这些污染物的潜在风险以及可能设计去除这些污染物的系统时都很重要。为了了解吸附的硝基吡喃的光转化机理，我们将：(1)考察吸附分子与不同底物的相互作用，并用吸收和荧光技术确定参与激发态的性质；(2)测定相对光降解速率；(3)根据时间分辨鉴定中间物种和三重态。 漫反射激光光谱和电子自旋共振；(4)鉴定稳定的产物，并将它们与溶液光化学中的结果进行比较。这一建议的一个基本目的是研究吸附剂的某些化学和物理性质，如组成、水含量、共吸附气体的存在、平均孔径和表面覆盖度对吸附的硝基吡喃的光物理和光化学过程的影响。此外，激光在模拟气溶胶的极性和非极性溶剂中照射产生的激发态和活性中间体将通过激光闪光瞬变光谱进行表征。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雾剂的有机液体核心中找到。

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.