Formation of Nitrated Polycyclic Aromatic Hydrocarbons (NPAHs) in Combustion Engine Exhaust Studied by Laser Photofragmentation

硝化多环芳烃（NPAHs）及其母体化合物PAHs可能是对人体健康危害最大的非生物类物质。很大一部分，超过三分之一的环境空气诱变潜力可归因于NPAHs。NPAHs是在NO2存在下燃烧形成的。内燃机废气中的NPAHs特别危险，因为它们附着在烟灰颗粒上，烟灰颗粒充当运输工具，穿过肺泡膜进入生物体并穿过红细胞壁。柴油微粒过滤器（DPF）中使用的一些策略利用了过量的二氧化氮。这导致了关于废气后处理系统中NPAHs可能的去新生形成的激烈讨论。然而，与其他空气污染物相比，对其发生、形成和汇的了解更加零碎和不完整。造成这种差距的原因是现有测量技术的半挥发性、不稳定性和缺乏灵敏度。二十多年来，在大多数这些方面没有取得重大进展。在废气中，基于过滤器的采样和随后的分析特别容易产生伪影。在这里，我们建议通过(1)提供一种快速、无伪影的NPAHs和PAHs测量方法来推进对NPAHs的认识，这将允许(2)在模拟汽车排气系统的流动反应器中受控条件下研究气溶胶颗粒物上PAH的npaah形成、降解和吸收NPAH，(3)直接、无伪影地研究内燃机排气系统上NPAHs和PAHs。这一艰巨的挑战将由激光光碎片（PF）完成。PF是化学键在光作用下的选择性断裂。选择性是由所选择的波长来定义的，它对应于一个特定的光子能量，这个光子能量等于化学结合能。在我们检测NPAH的情况下，产生的碎片，硝基和剩余的PAH，将通过它们的光学发射来检测，当碎片在激发态产生时，或者通过碎片离子产生的电流来检测。虽然PF的基本原理已经知道了几十年，但我们相信，通过新的仪器，这种技术可以成功地用于高灵敏度在线NPAH检测的常规应用。

Nitrated Polycyclic Aromatic Hydrocarbons (NPAHs), together with its parent compound PAHs, are probably the abiotic class of substances which is most harmful for human health. A large part, more than one third of the mutagen potential of ambient air is attributable to NPAHs. NPAHs are formed during combustion in the presence of NO2. NPAHs in combustion engine exhaust are particularly hazardous due to their attachment to soot particles, which act as transport vehicles across the alveolar membrane into the organism and across walls of red blood cells. Some strategies used in Diesel particulate filters (DPF) make use of excess NO2. This led to intense discussions about possible de-novo formation of NPAHs within an exhaust aftertreatment system. However, compared to other air pollutants, knowledge of occurrence, formation, and sinks is much more fragmentary and incomplete. The reason for this gap is semivolatility, instability, and lack of sensitivity of existing measuring techniques. For more than two decades, no major progress was achieved with regard to most of these aspects. In exhaust gas, filter-based sampling and subsequent analysis is particularly prone to artifact formation. Here, we propose to advance knowledge of NPAHs by (1) providing a fast, artifact-free measurement method for NPAHs and PAHs, which will allow to (2) study NPAH formation, degradation and sorption of NPAH from PAH on aerosol particulate matter under controlled conditions in a flow reactor, simulating an automotive exhaust system, (3) direct, artifact-free study of NPAHs and PAHs on the exhaust system of a combustion engine. This demanding challenge will be performed laser-photofragmentation (PF). PF is the selective fragmentation of a chemical bond by light. Selectivity is defined by the selected wavelength, corresponding to a specific photon energy, which is equal to the chemical binding energy. The generated fragments, in our case of NPAH detection, the nitro group and the remaining PAH, will be detected either by their optical emission, when the fragments are generated in the excited state, or by the current due to fragment ions. Although the fundamentals of PF are known for decades, we believe that by novel instrumentation, this techniques can successfully be implemented for the routine application of the challenging task of a highly sensitive on-line NPAH detection.