文摘
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鈥揚AH or NO3鈥揚AH 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鈥揘O2鈥揚AH 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鈥揘O2鈥揚AH 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鈥揚AH or NO3鈥揚AH 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鈥揜amsperger鈥揔assel鈥揗arcus (RRKM) theory.