Theoritical Investigation On Atmospheric Reactions Of Aromatic Nitro-PAHs And Furanaldehydes

Nitrated polycyclic aromatic hydrocarbons?nitro-PAHs?are important polycyclic aromatic hydrocarbon?PAH?derivatives containing two or more benzene rings.In the environment.PAHs.nitro-PAHs and other organic compounds are present in the form of a mixture.Generally,the concentration of nitro-PAHs is lower than that of PAHs.On the one hand.nitro-PAHs can be formed by nitration reactions of PAHs in the combustion process,such as diesel emissions,industrial emissions.residential heating.cooking.wood burning and so on.On the other hand,another source of nitro-PAHs is the secondary reactions of PAHs in the atmosphere.For example,nitro-PAHs can be generated via homogeneous reactions of PAHs with OH at daytime and NO₃ radicals at night-time.In addition.nitro-PAHs can also be produced by the heterogeneous reactions of PAHs with N₂O₅.PAHs are a kind of significant containments which have carcinogenicitv and mutagenicitv.The concentrations of nitro-PAHs are lower than that of PAHs.However.nitro-PAHs have more toxicity than parent PAHs and they may affect the formation of particles in the atmosphere.In order to control the air pollution effectively.we need to study the formation,migration and transformation of-PAHs and nitro-PAHs in the atmosphere.Nitro-PAHs are mixtures as present in the atmosphere and have low concentrations.Most of nitro-PAHs are difficult to separate from other organic substances.Therefore.the detection and analysis of nitro-PAHs have some limitations in the experiment.At the same time.a large number of experimental and theoretical studies just focus on the formation and degradation mechanism of monontro-PAHs.Whether dinitro-PAHs can generate from mononitro-PA Hs or not in the atmosphere is still unclear.Similar to PAHs.turanaldehydes are also a kind of atmospheric organic pollutants containing aromatic rings.The chemical reactions of furanaldehyde in the atmosphere promote the formation of secondary organic aerosols which can further affect the Earth's radiation balance.In addition,furanaldelihydes rise the health risks associated with photochemical smog.Many experimental and theoretical studies have been implemented to investigate the degradation mechanism of furanaldehydes.Furanaldehydes can react with OH radicals in the daytime and with Cl atom in coastal areas.However,the products of furanaldehydes with NO₃ radicals at night are still not clear.In addition,the heterogeneous reaction mechanism of furanaldehydes adsorbed on particle surface needs to be further explored.Therefore,in this study,the formation mechanism of nitro-PAHs.the renmoval process as well as heterogeneous reaction process of furanaldehyde were investigated by quantum chemical calculation.The corresponding kinetics and thermodynamic properties.the main reaction pathways and rate-determining steps were discussed in this study.1.The formation mechanism of dinitronaphthalene in the atmosphere initiated by OH and NO₃ radicalsIn this study.we investigated the formation mechanism of dinitro-naphthalenes initiated by OH and NO₃ radicals from 1-and 2-nitronaphthalene in the atmosphere by quantum chemical calculation at the level of BB1K/6-311+G?3d f.2 p?//BB1K/6-31+G?d.p?.The reaction rate constants of 1-nitronaphthalene and 2-nitronaphthalene with OH radicals were calculated by CVT/SVT method with polyrate program.The reaction rate constants of I-nitronaphthalene and 2-nitronaphthalene with NO₃ radicals were calculated by RRKM method with mesmer program.Water molecules play an essential role in the formation of dinitronaphthalenes.The main conclusions of this research are as follows:?1?The dinitrated products from 1-nitronaphthalene and 2-nitronaplithalene initiated by OH radicals are 1.2-.1.3-.1.5-.1.6-.1.7-dinitronaphthalene.The dinitrated products of 1-nitronaphthalene and 2-nitronaphthalene initiated by NO₃ radicals are 1.2-.1.3-.1.5-.1.6-.1.7-.1.9-.2.6-.2.7-dinitronaplhthalene.The formation mechanism of dinitro-naphthalenes contains several elementary steps such as the addition reactions of mononitro-naphthalenes with OH or NO₃ radicals,the addition reactions of NO₂ with OH-or NO₃-adducts.and the water or HNO₃ loss process.?2?Water molecule or waterdimer plays an essensial role in the water loss process of NO₂-OH-nitronaphalenes.The tension in the bonds of transition states has been reduced during catalytic reaction by water or water dimer.?3?The overall rate constants of the reactions of 1-nitronaphthalene and2-nitronaphthalene with OH radicals at 298 K.1 atm are 7.43×10^-13cm³ molecule^-1 S-1 and 7.48×10^-13cm³ molecule-2 s^-1.respectively.The overall rate constants of 1-nitronaphthalene and 2-nitronaphthalene with NO₃ radicals are 3.55×10-15 cm³ molecule^-1 s^-1 and 3.47×10-15 cm³ molecule^-1 s^-1,respectively.?4?Besides,the NO₂ addition reactions of OH-or NO₃-nitronaphthalene adducts may be competitive with O₂ addition at low concentration of NO₂,which needs to be further studied.2.The Formation Mechanism of Dinitro-pyrenes in the Atmosphere initiated by OH RadicalIn this study,we conducted a comprehensive theoretical study by DFT calculation on the atmospheric formation of dinitro-pyrenes from 1-nitropyrene.2-nitropyrene and 4-nitropyrene with OH radicals in the presence of NO₂ at the BB1K/6-311+G?3df,2p?//BB1K/6-31+G?d.p?level.The effect of water molecules in the formaiton process of dinitro-pyrenes was discussed.The branch and overall rate constants of OH addition and H abstraction were calculated by CVT theory with SCT tunneling correction.The conclusions obtained in this study are as follows:?1?The 1.2-and 1.7-dinitropyrene?from 1-nitropyrene?,2.7-dinitropyrene?from2-nitropyyrene?as well as 2.4-and 2.5-dinitropyrene?from 4-nitropyrene?are the main products.We found that water molecules can decrease the activation enthalpy of water loss process.and play an essential role in the formation of dinitropyrenes.?2?Water molecule plays an essensial role in the water loss process ofNO₂-OH-nitropyrenes.The tension in the bonds of transition states has been reduced during catalytic reaction by water.?3?The calculated overall rate constants for 1-,2-and 4-nitro pyrene initiated by OH radicals are 8.13×10^-13cm³ molecule^-1 s^-1.8.90×10^-13cm³ molecule^-1s^-1 and 1.50×10-12 cm³ molecule^-1 s^-1,respectively.The lifetime of 1-,2-and 4-nitropyrene determined by OH radicals at 298 K and 1 atm are 14.60 days.13.34 days and 7.91 days,respectively.?4?Compared with OH addition reaction of mononitro-naphthalenes.the potential barriers of OH addition reaction of mononitro-pyrenes are lower and release more energy.However,the potential barriers of water loss process to form dinitro-pyrenes are higher than that to form dinitro-naphthalenes.3.The Atmospheric Degradation Mechanism of 2-furanaldehyde Initiated by NO₃Radicals and the Heterogeneous Reaction Mechanism of 2-Furfuraldehyde Initiated by OH and NO₃ RadicalsIn this study.the removal process of 2-furanaldehvde initiated by NO₃ radicals in gas phase was investigated by quantum chemical calculation.At the same time,the rate constants of essential elementary reactions were calculated by RRKM theory.Based on the calculations in this study,the possible ring-close and ring-open products were discussed.The lifetime of 2-furanaldehvde determined by NO₃ radicals in the atmosphere was evaluated.The conclusions obtained in this study are as follows:?1?The degradation mechanism of 2-furanaldehyde initiated by NO₃ radicals may contain a series of elementary steps such as NO₃ addition reaction.H abstraction reaction.bimolecular reaction with NO.intramolecular addition reaction and so on.The dcegradation products were the ring-opening products and the ring-retaining products.?2?The overall rate constant of 2-furanaldehydehyde with NO₃ radicals is 1.04×10-12 cm³ molecule^-1 s^-1 at 298 K and 1 atm.Based on the rate constants calculated in this study,the atmospheric lifetime of furanaldehyde in the gas phase initiated by NO₃ radicals is 0.53 h.?3?Compared with the lifetime of 2-furanaldehyde determined by Cl atom?213 h?and OH radicals?4.9 h?,the lifetime of 2-furanaldehyde determined by NO₃ in this study is the lowest,indicating that the reaction with NO₃ radicals is the main removal pathway for 2-furanaldehyde at night-time.In this study,a model of black carbon was constructed by using the model of C₅₄H₁₈.We studied the adsorption of 2-furanaldehyde on the model of C₅₄H₁₈ or C₅₄H₁₈ modified by OH or COOH group.and the subsequent addition reactions with OH or NO₃ radicals were analyzed.This study was carried out at the M062x/def2SVP level.The conclusions obtained in this study are as follows:?1?Compared with OH group,the COOH group can increase the energy released from the adsorption reaction.thus the 2-furanaldehyde tends to adsorb on the surface of the black carbon particles.The possible reason is that the COOH group has more electrons than the OH group.?2?Similar to the gas phase reaction,the C2 and C5 sites are the predominant for 2-furanaldehyde with OH radicals on the model of C₅₄H₁₈ or C₅₄H₁₈ modified by OH or COOH groups.However,when OH radicals add to C2 site in the furan ring.the structure of this adduct is reversed in the heterogeneous reaction.The furan rine of OH-adduct is perpendicular to the C₅₄H₁₈ substrate.?3?The modification by OH or COOH group at the C2 site of C₅₄H₁₈ enhances the reactive activity of 2-furanaldehvde with OH radicals compared with the OH or COOH group modified at the Cl site of C₅₄H₁₈ Compared wih the modification of OH group on C2 site,the reactivity of the C sites in the furan ring except C5 site is increased with the modification of COOH group on C2 site.?4?Similar to the gas phase reaction.the C2.C3.and C5 sites are the predominant sites for 2-furanaldehyde with NO₃ radical on the model of C₅₄H₁₈ or C₅₄H₁₈ modified by OH or COOH groups.In this study,when NO₃ radical is added to C2 site in the furan ring.the structure of this NO₃-adduct is reversed in theheterogeneous reaction.The furan ring of NO;-adduct is perpendicular to the surface substrate.