Environment Research Institute, Shandong University , Jinan 250100, China.
Environ Sci Technol. 2014 May 6;48(9):5051-7. doi: 10.1021/es500453g. Epub 2014 Apr 11.
Nitro-PAHs are globally worrisome air pollutants because their high direct-acting mutagenicity and carcinogenicity. A mechanistic understanding of their formation is of crucial importance for successful prevention of their atmospheric pollution. Here, the formation of nitro-PAHs arising from the OH-initiated and NO3-initiated atmospheric reactions of PAHs was investigated by using quantum chemical calculations. It is widely assumed that OH or NO3 radicals attack on the C atoms of the aromatic rings in the PAH molecule, followed by the addition of NO2 to the OH-PAH or NO3-PAH adducts at the ortho position and the loss of water or nitric acid to form nitro-PAHs. However, calculations show that the direct loss of water from the OH-NO2-PAH adducts via the unimolecular decomposition is energetically unfavorable. This study reveals for the first time that water molecule plays an important catalytic effect on the loss of water from the OH-NO2-PAH adducts and promotes the formation of nitro-PAHs. In addition, the introduction of water unwraps new formation pathway through the addition of NO2 to the OH-PAH or NO3-PAH adduct at the para position. The individual and overall rate constants for the addition reactions of PAHs with OH and NO3 radicals were deduced by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory.
硝基金多环芳烃是全球令人担忧的空气污染物，因为它们具有很高的直接致突变性和致癌性。对其形成机制的理解对于成功预防其大气污染至关重要。本研究采用量子化学计算方法，研究了 OH 引发和 NO3 引发的多环芳烃大气反应生成硝基金多环芳烃的过程。人们普遍认为，OH 或 NO3 自由基攻击多环芳烃分子中芳香环上的 C 原子，然后在邻位加成 NO2 到 OH-PAH 或 NO3-PAH 加合物，同时失去水或硝酸生成硝基金多环芳烃。然而，计算表明，OH-NO2-PAH 加合物通过单分子分解直接失去水在能量上是不利的。本研究首次揭示了水分子在 OH-NO2-PAH 加合物失去水中发挥了重要的催化作用，促进了硝基金多环芳烃的生成。此外，水的引入通过在对位加成 NO2 到 OH-PAH 或 NO3-PAH 加合物，开辟了新的形成途径。通过 Rice-Ramsperger-Kassel-Marcus（RRKM）理论，推导出了 PAHs 与 OH 和 NO3 自由基加成反应的个体和总速率常数。
