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Download fileRole of Water Molecule in the Gas-Phase Formation Process of Nitrated Polycyclic Aromatic Hydrocarbons in the Atmosphere: A Computational Study
journal contribution
posted on 2014-05-06, 00:00 authored by Qingzhu Zhang, Rui Gao, Fei Xu, Qin Zhou, Guibin Jiang, Tao Wang, Jianmin Chen, Jingtian Hu, Wei Jiang, Wenxing WangNitro-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.
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Keywords
Nitrated Polycyclic Aromatic HydrocarbonsWater Moleculerate constants3 radicalsortho positionpara positionOHunimolecular decompositionPAH moleculenitric acidformation pathway3 radicals attackadductquantum chemical calculationscalculations showRRKMwater moleculeair pollutantsaddition reactionsC atoms