Density functional theory study on OH-initiated atmospheric oxidation of m-xylene

The OH-initiated oxidation reactions of m-xylene are investigated using density functional theory. The structures, energetics, and relative stability of the OH-m-xylene reaction intermediate radicals have been determined, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the oxidation. OH addition occurs preferentially at the two ortho positions with the branching ratios of 0.97, 0.02, and 0.01 for ortho, meta, and ipso additions, respectively. The results reveal that the OH-m-xylene-O2 peroxy radicals preferentially cyclize to form bicyclic radicals under atmospheric conditions rather than reacting with NO to lead to ozone formation, and the decomposition to O2 and the hydroxyl m-xylene adduct is competitive with the cyclization process. The bicyclic radicals of m-xylene formed from the major OH-addition pathways (i.e., ortho positions) are more probable to form bicyclic peroxy radicals by reacting with O2. This study provides thermochemical and kinetic data of the OH-initiated reactions of m-xylene for assessment of the role of aromatic hydrocarbons in photochemical production of ozone, toxic products, and secondary organic aerosols.     

Oxidation mechanism of aromatic peroxy and bicyclic radicals from OH-toluene reactions

Theoretical calculations have been performed to investigate mechanistic features of OH-initiated oxidation reactions of toluene. Aromatic peroxy radicals arising from initial OH and subsequent O(2) additions to the toluene ring are shown to cyclize to form bicyclic radicals rather than undergoing reaction with NO under atmospheric conditions. Isomerization of bicyclic radicals to more stable epoxide radicals possesses significantly higher barriers and, hence, has slower rates than O(2) addition to form bicyclic peroxy radicals. At each OH attachment site, only one isomeric pathway via the bicyclic peroxy radical is accessible to lead to ring cleavage. The study provides thermochemical and kinetic data for quantitative assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from toluene oxidation.     

Theoretical investigation on the detailed mechanism of the OH‐initiated atmospheric photooxidation of o‐xylene

The reaction mechanism for o‐xylene with OH radical and O₂ was studied by density functional theory (DFT) method. The geometries of the reactants, intermediates, transition states, and products were optimized at B3LYP/6‐31G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single‐point calculations for all the stationary points were carried out at the B3LYP/6‐311++G(2df,2pd) level using the B3LYP/6‐31G(d,p) optimized geometries. Reaction energies for the formation of the aromatic intermediate radicals have been obtained to determine their relative stability and reversibility, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the o‐xylene oxidation. The results of the theoretical study indicate that OH addition to o‐xylene forms ipso, meta, and para isomers of o‐xylene‐OH adducts, and the ipso o‐xylene adduct is the most stable among these isomers. Oxygen is expected to add to the o‐xylene‐OH adducts forming o‐xylene peroxy radicals. And subsequent ring closure of the peroxyl radicals to form bicyclic radicals. With relatively low barriers, isomerization of the o‐xylene bicyclic radicals to more stable epoxide radicals likely occurs, competing with O₂ addition to form bicyclic peroxy radicals. The study provides thermochemical data for assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from o‐xylene photooxidation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Atmospheric oxidation mechanism of naphthalene initiated by OH radical. A theoretical study

The atmospheric oxidation mechanism of naphthalene (Nap) initiated by the OH radical is investigated using density functional theory at B3LYP and BB1K levels. The initial step is dominated by OH addition to the C(1)-position of Nap, forming radical C(10)H(8)-1-OH (R1), followed by the O(2) additions to the C(2) position to form peroxy radical R1-2OO, or by the hydrogen abstraction by O(2) to form 1-naphthol. In the atmosphere, R1-2OO will react with NO to form R1-2O, undergo intramolecular hydrogen transfer from -OH to -OO to form R1-P2O1 radicals, or possibly undergo ring-closure to R1-29OO bi-cyclic radical; while the formation of other bi-cyclic intermediate radicals is negligible because of the extremely high Gibbs energy barriers of >100 kJ mol(-1) (relative to R1+O(2)). The mechanism is different from the oxidation mechanism of benzene, where the bi-cyclic intermediates play an important role. Radicals R1-P2O1 will dissociate to 2-formylcinnamaldehyde, while R1-2O will be transformed to stable products C(10)H(6)O(3) via epoxide-like intermediates. A few reaction pathways suggested in previous experimental studies are found to be invalid.     

The Atmospheric Oxidation Mechanism of Benzyl Alcohol Initiated by OH Radicals: The Addition Channels

Benzyl alcohol (BA) is present in indoor atmospheres, where it reacts with OH radicals and undergoes further oxidation. A theoretical study is carried out to elucidate the reaction mechanism and to identify the main products of the oxidation of BA that is initiated by OH radicals. The reaction is found to proceed by H‐abstraction from the CH₂ group (25 %) and addition to the ipso (60 %) and ortho (15 %) positions of the aromatic ring. The BA–OH adducts react further with O₂ via the bicyclic radical intermediates—the same way as for benzene—forming mainly 3‐hydroxy‐2‐oxopropanal and butenedial. If NO_x is low, the bicyclic peroxy radicals undergo intramolecular H‐migration, forming products containing OH, OOH, and CH₂OH/CHO functional groups, and contribute to secondary organic aerosol (SOA) formation.     

羟基自由基引发的邻二甲苯大气氧化机理

采用量子化学、过渡态理论和单分子反应理论计算,研究了由羟基(OH)自由基引发的邻二甲苯(oX)大气氧化降解机理.在M06-2X/6-311++G(2df, 2p)水平上优化了反应物、过渡态和产物的结构,在ROCBSQB3水平上计算了反应势能面.采用过渡态理论计算了各个可能反应步骤的速率常数和反应通道的分支比,同时还采用单分子反应理论(RRKM-ME)计算探讨了反应的压力效应.计算发现,在大气中,邻二甲苯与OH的反应以苯环加成为主,首先形成两个加和物oX-1-OH (R1)和oX-3-OH (R3),它们随后与大气中的氧气发生反应.R1和R3与O₂可直接发生不可逆直接夺氢生成二甲基苯酚,或和O₂的可逆加成,生成双环自由基中间体.双环自由基将与大气中的氧气结合,形成双环过氧自由基,接着与NO或HO₂反应生成有机硝酸酯或有机过氧化氢化合物,或被还原为双环烷氧自由基,并最终生成产物,包括丁二酮、丁烯二醛、甲基乙二醛、4-氧-2-戊烯醛、2, 3-环氧丁二醛以及少量的乙二醛.这些产物中有机过氧化氢和甲基乙二醛被认为对二次气溶胶有较大的贡献.结合理论计算和文献报道的实验结果,提出了新的oX大气氧化机理,预测了在高NO浓度条件下可能产物的分支比,并与文献报道结果相比较.最后还讨论了温度对反应机理的影响.     

Comprehensive NO-dependent study of the products of the oxidation of atmospherically relevant aromatic compounds

A comprehensive product study, performed via the turbulent flow chemical ionization mass spectrometry (TF-CIMS) technique, of the primary OH-initiated oxidation of many of the atmospherically abundant aromatic compounds was performed. The bicyclic peroxy radical intermediate, a key proposed intermediate species in the Master Chemical Mechanism (MCM) for the atmospheric oxidation of aromatics, was detected in all cases, as were stable bicyclic species. The NO product yield dependences suggest a potential role for bicyclic peroxy radical + HO(2) reactions at high HO(2)/NO ratios, which are postulated to be a possible source of the inconsistencies between previous environmental chamber results and predictions from the MCM for ozone production and OH reactivity. The TF-CIMS product yield results are also compared to previous environment chamber results and to the latest MCM parametrization.     

Nighttime radical observations and chemistry

The nitrate radical, NO(3), is photochemically unstable but is one of the most chemically important species in the nocturnal atmosphere. It is accompanied by the presence of dinitrogen pentoxide, N(2)O(5), with which it is in rapid thermal equilibrium at lower tropospheric temperatures. These two nitrogen oxides participate in numerous atmospheric chemical systems. NO(3) reactions with VOCs and organic sulphur species are important, or in some cases even dominant, oxidation pathways, impacting the budgets of these species and their degradation products. These oxidative reactions, together with the ozonolysis of alkenes, are also responsible for the nighttime production and cycling of OH and peroxy (HO(2) + RO(2)) radicals. In addition, reactions of NO(3) with biogenic hydrocarbons are particularly efficient and are responsible for the production of organic nitrates and secondary organic aerosol. Heterogeneous chemistry of N(2)O(5) is one of the major processes responsible for the atmospheric removal of nitrogen oxides as well as the cycling of halogen species though the production of nitryl chloride, ClNO(2). The chemistry of NO(3) and N(2)O(5) is also important to the regulation of both tropospheric and stratospheric ozone. Here we review the essential features of this atmospheric chemistry, along with field observations of NO(3), N(2)O(5), nighttime peroxy and OH radicals, and related compounds. This review builds on existing reviews of this chemistry, and encompasses field, laboratory and modelling work spanning more than three decades.     

Quantum chemical and master equation simulations of the oxidation and isomerization of vinoxy radicals

The vinoxy radical, a common intermediate in gas-phase alkene ozonolysis, reacts with O2 to form a chemically activated alpha-oxoperoxy species. We report CBS-QB3 energetics for O2 addition to the parent (*CH2CHO, 1a), 1-methylvinoxy (*CH2COCH3, 1b), and 2-methylvinoxy (CH3*CHCHO, 1c) radicals. CBS-QB3 predictions for peroxy radical formation agree with experimental data, while the G2 method systematically overestimates peroxy radical stability. RRKM/master equation simulations based on CBS-QB3 data are used to estimate the competition between prompt isomerization and thermalization for the peroxy radicals derived from 1a, 1b, and 1c. The lowest energy isomerization pathway for radicals 4a and 4c (derived from 1a and 1c, respectively) is a 1,4-shift of the acyl hydrogen requiring 19-20 kcal/mol. The resulting hydroperoxyacyl radical decomposes quantitatively to form *OH. The lowest energy isomerization pathway for radical 4b (derived from 1b) is a 1,5-shift of a methyl hydrogen requiring 26 kcal/mol. About 25% of 4a, but only approximately 5% of 4c, isomerizes promptly at 1 atm pressure. Isomerization of 4b is negligible at all pressures studied.     

Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance

Organic peroxy radicals (often abbreviated RO(2)) play a central role in the chemistry of the Earth's lower atmosphere. Formed in the atmospheric oxidation of essentially every organic species emitted, their chemistry is part of the radical cycles that control the oxidative capacity of the atmosphere and lead to the formation of ozone, organic nitrates, organic acids, particulate matter and other so-called secondary pollutants. In this review, laboratory studies of this peroxy radical chemistry are detailed, as they pertain to the chemistry of the atmosphere. First, a brief discussion of methods used to detect the peroxy radicals in the laboratory is presented. Then, the basic reaction pathways - involving RO(2) unimolecular reactions and bimolecular reactions with atmospheric constituents such as NO, NO(2), NO(3), O(3), halogen oxides, HO(2), and other RO(2) species - are discussed. For each of these reaction pathways, basic reaction rates are presented, along with trends in reactivity with radical structure. Focus is placed on recent advances in detection methods and on recent advances in our understanding of radical cycling processes, particularly pertaining to the complex chemistry associated with the atmospheric oxidation of biogenic hydrocarbons.     

Atmospheric fate of methacrolein. 1. Peroxy radical isomerization following addition of OH and O2

Peroxy radicals formed by addition of OH and O(2) to the olefinic carbon atoms in methacrolein react with NO to form methacrolein hydroxy nitrate and hydroxyacetone. We observe that the ratio of these two compounds, however, unexpectedly decreases as the lifetime of the peroxy radical increases. We propose that this results from an isomerization involving the 1,4-H-shift of the aldehydic hydrogen atom to the peroxy group. The inferred rate (0.5 ± 0.3 s(-1) at T = 296 K) is consistent with estimates obtained from the potential energy surface determined by high level quantum calculations. The product, a hydroxy hydroperoxy carbonyl radical, decomposes rapidly, producing hydroxyacetone and re-forming OH. Simulations using a global chemical transport model suggest that most of the methacrolein hydroxy peroxy radicals formed in the atmosphere undergo isomerization and decomposition.     

Atmospheric chemistry of 4:2 fluorotelomer alcohol (n-C4F9CH2CH2OH): products and mechanism of Cl atom initiated oxidation in the presence of NOx

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C(4)F(9)CH(2)CH(2)OH, 4:2 FTOH) in the presence of NO(x) in 700 Torr of N(2)/O(2) diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C(4)F(9)CH(2)CH(2)OH to give C(4)F(9)CH(2)C(*)HOH radicals which add O(2) to give chemically activated alpha-hydroxyperoxy radicals, [C(4)F(9)CH(2)C(OO(*))HOH]*. In 700 Torr of N(2)/O(2) at 296 K, approximately 50% of the [C(4)F(9)CH(2)C(OO(*))HOH]* radicals decompose "promptly" to give HO(2) radicals and C(4)F(9)CH(2)CHO, the remaining [C(4)F(9)CH(2)C(OO(*))HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C(4)F(9)CH(2)C(OO(*))HOH. Decomposition to HO(2) and C(4)F(9)CH(2)CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C(4)F(9)CH(2)C(O(*))HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C(4)F(9)CH(2)(*). The primary products of 4:2 FTOH oxidation in the presence of excess NO(x) are C(4)F(9)CH(2)CHO, C(4)F(9)CHO, and HCOOH. Secondary products include C(4)F(9)CH(2)C(O)O(2)NO(2), C(4)F(9)C(O)O(2)NO(2), and COF(2). In contrast to experiments conducted in the absence of NO(x), there was no evidence (<2% yield) for the formation of the perfluorinated acid C(4)F(9)C(O)OH. The results are discussed with regard to the atmospheric chemistry of fluorotelomer alcohols.     

Pressure dependence of pentyl nitrate formation from the OH Radical-initiated reaction of n-pentane in the presence of NO

The formation yields of 2- and 3-pentyl nitrate from the reactions of 2- and 3-pentyl peroxy radicals with NO have been measured at room temperature over the pressure range 51-744 Torr of N2 + O2, using the OH radical-initiated reaction of n-pentane to generate the pentyl peroxy radicals. The influence of 2- and 3-pentyl nitrate formation from the reaction of 2- and 3-pentoxy radicals with NO2 was investigated by conducting experiments with the initial CH3ONO (the OH radical precursor) and NO concentrations being varied by a factor of 5-10. From experiments carried out with low initial CH3ONO and NO concentrations, the measured yields of 2-pentyl nitrate and 3-pentyl nitrate, defined as ([pentyl nitrate] formed)/([n-pentane] reacted), each increase with increasing total pressure, from 1.10 +/- 0.09% and 1.11 +/- 0.10%, respectively, at 51 +/- 1 Torr of O2 to 5.48 +/- 0.51% and 4.07 +/- 0.31%, respectively, at 737 +/- 4 Torr of N2 + O2.     

On the mechanism of thermal oxidation of methane

Using the method of freezing radicals in conjunction with ESR spectroscopic measurements, the kinetics of the thermal oxidation of methane has been studied under atmospheric pressure depending on the temperature, composition of the mixture, and nature of the surface of the reaction vessel. It has been shown that in a reactor treated with boric acid, the intermediates methylhydroperoxide and hydrogen peroxide are responsible for chain branching. It has been established that the leading active centers of the reaction are the HO₂ radicals, while chain branching occurs as a result of the decomposition of peroxy compounds—methylhydroperoxide and hydrogen peroxide. In reactors treated with potassium bromide, the concentrations of radicals and peroxy compounds were found to be lower than the sensitivity of the method of measurement. Computations were performed for the scheme of methane oxidation at 738 K for a reactor treated with boric acid. Satisfactory agreement was found between the experimental and computed kinetic curves of accumulation of main intermediates CH₂O, H₂O₂, CH₃OOH. The influence of their addition on the kinetics of the reaction has been considered. It has been shown that the addition of formaldehyde does not lead to chain branching, however; it contributes to the formation of those peroxy compounds that bring about chain branching. Mathematical modeling confirmed conclusions made on the basis of experimental data concerning the nature of the leading active centers and the products that are responsible for the degenerate chain branching.     

Unusually fast 1,6-h shifts of enolic hydrogens in peroxy radicals: formation of the first-generation C2 and C3 carbonyls in the oxidation of isoprene

In a theoretical investigation using the CBS-QB3//UB3LYP/6-31+G** method supported by higher-level computations such as CBS-QB3//UQCISD/6-31+G**, the 1,6-H shifts of the enolic hydrogen in peroxy radicals of the type Z-HO-CH═CH-CH(2)-OO(?) were found to face exceptionally low energy barriers of only about 11 kcal mol(-1)--i.e., 6-9 kcal mol(-1) lower than the barriers for similar shifts of alkane hydrogens--such that they can proceed at unequaled rates of order 10(5) to 10(6) s(-1) at ambient temperatures. The unusually low barriers for enolic 1,6-H shifts in peroxy radicals, characterized here for the first time to our knowledge, are rationalized. As cases in point, the secondary peroxy radicals Z-HO-CH═C(CH(3))-CH(OO(?))-CH(2)OH (case A) and Z-HO-CH═CH-C(CH(3))(OO(?))-CH(2)OH (case B) derived from the primary Z-δ-hydroxy-peroxy radicals in the oxidation of isoprene, are predicted to undergo 1,6-H shifts of their enolic hydrogens at TST-calculated rates in the range 270-320 K of k(T)(A) = 5.4 × 10(-4) × T(5.04) × exp(-1990/T) s(-1) and k(T)(B) = 109 × T(3.13) × exp(-3420/T) s(-1), respectively, i.e., 2.0 × 10(6) and 6.2 × 10(4) s(-1), respectively, at 298 K, far outrunning in all relevant atmospheric and laboratory conditions their reactions with NO proposed earlier as their dominant pathways (Dibble J. Phys. Chem. A 2004, 108, 2199). These fast enolic-H shifts are shown to provide the explanation for the first-generation formation of methylglyoxal + glycolaldehyde, and glyoxal + hydroxyacetone in the oxidation of isoprene under high-NO conditions, recently determined by several groups. However, under moderate- and low-NO atmospheric conditions, the fast interconversion and equilibration of the various thermally labile, initial peroxy conformers/isomers from isoprene and the isomerization of the initial Z-δ-hydroxy-peroxy radicals, both recently proposed by us (Peeters et al. Phys. Chem. Chem. Phys. 2009, 11, 5935), are expected to substantially reduce the yields of the small carbonyls at issue.     

Peroxy and alkoxy radicals from 2-methyl-3-buten-2-ol

Quantum mechanical calculations were used to determine the structure and energetics of peroxy radicals (P1 and P2) and alkoxy radicals (A1-A3) formed in the atmospheric degradation of 2-methyl-3-buten-2-ol. At the level of theory employed (B3LYP/6-31G(d,p)) low energy conformers were identified with zero, one, or two hydrogen bonds. The beta C-C scission (decomposition) reactions are computed to occur with low barriers, and the 1,5 H-shift (isomerization) reaction of A2 is computed to be of negligible importance. Scission 2 of A2 is computed to be about 93% of the fate of A2, with the balance being scission 1. The new BB1K functional of Truhlar was employed to investigate activation barriers for single intramolecular H-atom transfers across the OH...O* hydrogen bonds, but the barriers to these reactions appear to be too high for these reactions to be important. Extensive searches for transition states for simultaneous double intramolecular H-atom transfer across OH...OH...O* hydrogen bond pairs were unsuccessful.     

Computations on the A-X transition of isoprene-OH-O2 peroxy radicals

Calculations are carried out on the A state of HO2, CH3O2, and CH3CH2O2 and 10 isomers and conformers of the isoprene-OH-O2 peroxy radicals derived from OH addition to isoprene (2-methyl-1,3-butadiene). In addition to calculating vertical and adiabatic excitation energies, we consider the effect of excitation on molecular structure, and examine the OO stretching frequencies, which are known to be major features in the absorption spectra of the A states of the smaller radicals. The two methods used are the configuration interaction with single excitations (CIS) method and time-dependent density functional theory (TD-DFT), both with a range of basis sets up to 6-311++G(2df,2pd). TD-DFT overestimates excitation energies considerably, while CIS tends to underestimate them slightly. TD-DFT does seem to capture the trend in excitation energy vs. size for the smaller peroxy radicals. Conformation and configuration strongly affect the excitation energies of the peroxy radicals from isoprene. CIS calculations indicate that the intramolecular OH--O hydrogen bonds, present in the ground state of some peroxy radicals from isoprene, are weakened or broken in the excited state, while TD-DFT calculations suggest they are retained.     

Mechanisms of water oxidation catalyzed by ruthenium diimine complexes

(18)O-isotope-labeling studies have led to the conclusion that there exist two major pathways for water oxidation catalyzed by dimeric ruthenium ions of the general type cis, cis-[L2Ru(III)(OH2)]2O(4+). We have proposed that both pathways involve concerted addition of H and OH fragments derived from H 2O to the complexes in their four-electron-oxidized states, i.e., [L2Ru(V)(O)]2O(4+), ultimately generating bound peroxy intermediates that decay with the evolution of O2. The pathways differ primarily in the site of addition of the OH fragment, which is either a ruthenyl O atom or a bipyridine ligand. In the former case, water addition is thought to give rise to a critical intermediate whose structure is L2Ru(IV)(OH)ORu(IV)(OOH)L2(4+); the structures of intermediates involved in the other pathway are less well defined but may involve bipyridine OH adducts of the type L2Ru(V)(O)ORu(IV)(OH)(L(*)OH)L(4+), which could react further to generate unstable dioxetanes or similar endoperoxides. Published experimental and theoretical support for these pathways is reviewed within the broader context of water oxidation catalysis and related reactions reported for other diruthenium and group 8 monomeric diimine-based catalysts. New experiments that are designed to probe the issue of bipyridine ligand "noninnocence" in catalysis are described. Specifically, the relative contributions of the two pathways have been shown to correlate with substituent effects in 4,4'- and 5,5'-substituted bipyridine complexes in a manner consistent with the formation of a reactive OH-adduct intermediate in one of the pathways, and the formation of OH-bipyridine adducts during catalytic turnover has been directly confirmed by optical spectroscopy. Finally, a photosensitized system for catalyzed water oxidation has been developed that allows assessment of the catalytic efficiencies of the complex ions under neutral and alkaline conditions; these studies show that the ions are far better catalysts than had previously been assumed based upon reported catalytic parameters obtained with strong oxidants in acidic media.     

Tertiary aminomethylphenols and methylene bisphenols with isobornyl substituents in the reaction with diphenylpicrylhydrazyl and peroxy radicals in ethylbenzene

The effect of the structure of aminomethylphenols and methylene bisphenols with isobornyl substituents on their reactivity in interactions with peroxy radicals in ethylbenzene and with 1,1-diphenyl-2-picrylhydrazyl (DPPH) is studied. Isobornylphenols with o-aminomethyl substituents, as opposed to p-aminomethyl derivatives, were found to possess rather low activity in the initiated oxidation of ethylbenzene, due to the formation of intramolecular hydrogen bonds between the hydrogen atom of the OH group and the nitrogen atom of the aminomethyl substituent. An increase in activity of o-aminomethyl-substituted phenols with increasing polarity of the medium is observed in the reaction with DPPH. The reaction rate constants for the interaction between two isomeric 2,2′- and 4,4′-methylene-bisphenols having isobornyl moieties and ethylbenzene peroxy radicals are measured. The ratio between activities of the first and second OH groups in 2,2-methylene-bisphenol is shown to be close to 50.     

Kinetics study of the aromatic bicyclic peroxy radical + NO reaction: overall rate constant and nitrate product yield measurements

The measurements of the overall bicyclic peroxy radical + NO rate constant for the 1,3,5-trimethylbenzene (1,3,5-TMB) system and of the nitrate product yields for the benzene, toluene, p-xylene, and 1,3,5-TMB systems were performed via the turbulent flow chemical ionization mass spectrometry technique. While the overall rate constant was found to be consistent with the value used in the most detailed aromatic oxidation kinetic model (Master Chemical Mechanism, MCM), the nitrate product yields were found to be generally lower than predicted by the MCM and to have a different aromatic species-specific dependence than the MCM predicts.