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The degradation of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere can lead to toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. This paper aimed to investigate the mechanism of the OH-initiated oxidation degradation of benzo[α]pyrene (BaP), a cancer risk indicator. High-accuracy molecular orbital calculations were carried out, and all of the possible degradation pathways were discussed. The theoretical results were compared with the available experimental observation. The possible secondary reactions were also investigated. The rate constants of the crucial elementary steps were evaluated by using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The dominant degradation products involve benzo[α]pyren-ol, nitro-benzo[α]pyrene, benzo[α]pyrene-7,10-dione as well as several ring-opened products such as alkyl substituted benzanthraldehyde et al. In particular, water plays an important role in the degradation pathways leading to the formation of nitro-benzo[α]pyrene. This work provides a comprehensive investigation of the OH-initiated degradation of BaP and should help to clarify its potential risk. [ABSTRACT FROM AUTHOR]

Due to its prevalent presence, it is critical to clarify the atmospheric fate of acenaphthylene (Ary). In this paper, the reaction mechanism of the gas-phase ozonolysis of Ary was investigated by using quantum chemistry methods. Possible reaction pathways were discussed, and the theoretical results were compared with the available experimental data. The rate constants of the crucial elementary reactions were determined by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The main products include secondary ozonide, naphthalene-1,8-dicarbaldehyde, 1,8-naphthalic anhydride, oxaacenaphthylene-2-one, 1-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, and α-hydroxyhydroperoxide. The reaction of the unsaturated cyclo-pentafused ring with O3 is the dominant pathway. The overall rate constant of the O 3 addition reaction is 5.31 × 10 − 16 cm 3 molecule − 1 s − 1 at 298 K and 1 atm. The atmospheric lifetime of Ary determined by O 3 is about 0.75 h. This work provides a comprehensive investigation of the ozonolysis of Ary and should help to understand its atmospheric fate. [ABSTRACT FROM AUTHOR]

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) have become a serious environmental concern due to their widespread occurrence and dioxin-like toxicities. In this work, the mechanism of the OH-initiated atmospheric oxidation degradation of 9,10-dichlorophenanthrene (9,10-Cl 2 Phe) was investigated by using high-accuracy quantum chemistry calculations. The rate constants of the crucial elementary reactions were determined by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The theoretical results were compared with the available experimental data. The main oxidation products are a group of ring-retaining and ring-opening compounds including chlorophenanthrols, 9,10-dichlorophenanthrene-3,4-dione, dialdehydes, chlorophenanthrenequinones, nitro-9,10-Cl 2 Phe and epoxides et al. The overall rate constant of the OH addition reaction is 2.35 × 10 − 12 cm 3 molecule − 1 s − 1 at 298 K and 1 atm. The atmospheric lifetime of 9,10-Cl 2 Phe determined by OH radicals is about 5.05 days. This study provides a comprehensive investigation of the OH-initiated oxidation degradation of 9,10-Cl 2 Phe and should contribute to clarifying its atmospheric fate. [ABSTRACT FROM AUTHOR]

The atmospheric oxidation of polycyclic aromatic hydrocarbons (PAHs) can generate toxic derivatives which contribute to the carcinogenic potential of particulate organic matter. In this work, the mechanism of the OH-initiated atmospheric oxidation of fluoranthene (Flu) was investigated by using high-accuracy molecular orbital calculations. All of the possible oxidation pathways were discussed, and the theoretical results were compared with the available experimental observation. The rate constants of the crucial elementary reactions were evaluated by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The main oxidation products are a range of ring-retaining and ring-opening chemicals containing fluoranthols, fluoranthones, fluoranthenequinones, nitro-fluoranthenes, dialdehydes and epoxides. The overall rate constant of the OH addition reaction is 1.72 × 10 − 11 cm 3 molecule − 1 s − 1 at 298 K and 1 atm. The atmospheric lifetime of Flu determined by OH radicals is about 0.69 days. This work provides a comprehensive investigation of the OH-initiated oxidation of Flu and should help to clarify its atmospheric conversion. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quantum chemical methods are employed to study the title reactions. [•] Major products of the title reactions are indicated in this study. [•] The rate constant of title reaction is calculated in the first time. [•] The lifetime of DMP is also determined. [ABSTRACT FROM AUTHOR]

The ozonolysis of 2,3,7,8-tetra-chlorodibenzo-p-dioxin (2,3,7,8-TCDD) is an efficient degradation way in the atmosphere. The ozonolysis process and possible reactions path of Criegee Intermediates with NO and H 2 O are introduced in detail at the method of MPWB1K/6-31+G(d,p)//MPWB1K/6-311+G(3df,2p) level. In ozonolysis, H 2 O is an important source of OH radical formation and initiated the subsequent degradation reaction. The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was applied to calculate rate constants with the temperature ranging from 200 to 600 K. The rate constant of reaction between 2,3,7,8-TCDD and O 3 is 4.80 × 10 −20 cm 3 /(mole·sec) at 298 K and 760 Torr. The atmospheric lifetime of the reaction species was estimated according to rate constants, which is helpful for the atmospheric model study on the degradation and risk assessment of dioxin. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gas-phase formation of PBDD/Fs from 2,4,5-TBP and 3,4-DBP was studied by DFT. [•] Only BPs with bromine at the ortho position are capable of forming PBDDs. [•] The formation of PBDDs dominates over the formation of PBDFs. [•] The meta bromine facilitates the dimerization of BP radicals, whereas the para and ortho ones suppress it. [•] The formation of PBDDs from BPs is easier compared to that of the analogous PCDDs from CPs. [Copyright &y& Elsevier]

Abstract: The bromophenoxy radicals (BPRs) are key intermediate species involved in the formation of polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs). In this work, the formation of BPRs from the complete series reactions of 19 bromophenol (BP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method and the direct dynamics method. The geometries and frequencies of the reactants, transition states, and products were calculated at the MPWB1K/6-31+G(d,p) level, and the energetic parameters were further refined by the MPWB1K/6-311+G(3df,2p) method. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution over a wide temperature range of 600–1200K. The present study indicates that the reactivity of the O–H bonds in BPs as well as the formation potential of BPRs from BPs is strongly related to the bromine substitution pattern. The obtained results can be used for future estimates of PBDD/F emissions quantity based on the well estimated PCDD/F inventory. [Copyright &y& Elsevier]