Atmospheric oxidation of gaseous anthracene and phenanthrene initiated by OH radicals

作者：Zeng, Min; Liao, Zhihong; Wang, Liming^*

来源：Atmospheric Environment, 2020, 234: 117587.

DOI：10.1016/j.atmosenv.2020.117587

• PAHs
• OH Radical
• Oxidation mechanism
• Nitro-PAHs
• Oxygenated PAHs

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. In the atmosphere, PAHs are oxidized to oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs). However, the formation mechanism of OPAHs and NPAHs are unclear. Here we investigated the oxidation mechanism of anthracene (ANT) and phenanthrene (PHE) initiated by OH radical using quantum chemistry and chemical kinetic calculations. The oxidation starts by forming PAH-OH adducts which then react with O-2 and NO2 in the atmosphere. Reactions of PAH-OH and O-2 start mainly by reversible OO addition, forming PAH-OH-OO radicals, which then undergo backward decomposition to PAH-OH + OO, forward unimolecular isomerizations to OPAH products, and bimolecular reaction with NO. Effective rate of each route depends on the equilibrium constant of O-2 addition and the rates of forward unimolecular and bimolecular reactions of PAH-OH-OO. We predicted that ANT-9-OH, PHE-4-OH, and PHE-1-OH would react slowly with O-2 with effective rates at 298 K of similar to 18, similar to 50, and similar to 18 s(-1), forming OPAH (2,10-AQ for ANT); therefore, they would also react with atmospheric NO2, forming significant amounts of 9-NANT, 3-NPHE, and 2-NPHE, respectively. ANT-1-OH and PHE-10-OH would react rapidly with O-2, forming OPAHs only. Predicted formation of 9-NANT and 3-NPHE agrees with field measurements in urban atmosphere where NPAHs are more likely formed from reactions of PAHs with OH and/or NO3. On the other hand, observation of 9-NPHE might suggest a primary source of NPAHs such as biomass burning because 9-NPHE is highly unlikely formed in OH- and/or NO3-initiated reaction of PHE.