OH radical-initiated reaction of 3-hexene-2,5-dione: formation of methylglyoxal

3-Hexene-2,5-dione [CH3C(O)CH=CHC(O)CH3] and other unsaturated 1,4-dicarbonyls are formed from the atmospheric photooxidations of aromatic hydrocarbons. We have reinvestigated the formation of methylglyoxal from the gas-phase reaction of OH radicals with 3-hexene-2,5-dione in the presence of NO at room temperature and atmospheric pressure of air using in situ Fourier transform infrared spectroscopy. No evidence for the formation of methylglyoxal was obtained, with the IR spectra showing that methylglyoxal is, at most, a minor reaction product with a molar formation yield of <10% (and more likely <1%). This confirms our earlier study (Tuazon et al. Environ. Sci. Technol. 1985, 19, 265) and suggests that the CH3C(O)CH(OH)CHO and CH3C(O)CH(OH)CH(ONO2)C(O)CH3 observed by Bethel et al. (Environ. Sci. Technol. 2001, 35, 4477) are the major first-generation reaction products.     

Kinetics and products of the reaction of OH radicals with 3-methoxy-3-methyl-1-butanol

3-Methoxy-3-methyl-1-butanol [CH(3)OC(CH(3))(2)CH(2)CH(2)OH] is used as a solvent for paints, inks, and fragrances and as a raw material for the production of industrial detergents. A rate constant of (1.64 ± 0.18) × 10(-11) cm(3) molecule(-1) s(-1) for the reaction of 3-methoxy-3-methyl-1-butanol with OH radicals has been measured at 296 ± 2 K using a relative rate method, where the indicated error is the estimated overall uncertainty. Acetone, methyl acetate, glycolaldehyde, and 3-methoxy-3-methylbutanal were identified as products of the OH radical-initiated reaction, with molar formation yields of 3 ± 1%, 35 ± 9%, 13 ± 3%, and 33 ± 7%, respectively, at an average NO concentration of 1.3 × 10(14) molecules cm(-3). Using a 12-h average daytime OH radical concentration of 2 × 10(6) molecules cm(-3), the calculated lifetime of 3-methoxy-3-methyl-1-butanol with respect to reaction with OH radicals is 8.5 h. Potential reaction mechanisms are discussed.     

Kinetics and products of photolysis and reaction with OH radicals of a series of aromatic carbonyl compounds

We have investigated the photolysis and OH radical reactions of phthaldialdehyde, 2-acetylbenzaldehyde, and 1,2diacetylbenzene, atmospheric reaction products of naphthalene and alkylnaphthalenes, and of phthalide, a photolysis product of phthaldialdehyde. Using a relative rate method with 1,2,4-trimethylbenzene and 2,2,3,3-tetramethylbutane as reference compounds, measured rate constants for the gas-phase OH radical reactions (in units of 10(-12) cm3 molecule(-1) s(-1)) were as follows: phthaldialdehyde, 23 +/- 3; 2-acetylbenzaldehyde, 17 +/- 3; 1,2-diacetylbenzene, < 1.2; and phthalide, < 0.8. Blacklamp irradiation showed that phthaldialdehyde and 2-acetylbenzaldehyde photolyze, and, combined with absorption spectra measured in n-hexane solution, average photolysis quantum yields of 0.19 and 0.21, respectively, were derived (290-400 nm). No evidence for photolysis of 1,2-diacetylbenzene or phthalide by blacklamps was obtained. The major atmospheric loss process of phthaldialdehyde and 2-acetylbenzaldehyde are estimated to be by photolysis, with photolysis lifetimes of 1.4-1.5 h for a 12-hr average NO2 photolysis rate of 0.312 min(-1). Phthalic anhydride was the major observed product from the OH radical-initiated reactions of all four compounds and was also formed from photolysis of phthaldialdehyde and 2-acetylbenzaldehyde. The major photolysis products observed were phthalide from phthaldialdehyde and 3-methylphthalide from 2-acetylbenzaldehyde.     

Development of an analytical method and survey of foods for furan, 2-methylfuran and 3-methylfuran with estimated exposure

Furan has been found to form in foods during thermal processing. These findings, a classification of furan as a possibly carcinogenic to humans, and a limited amount of data on the concentration of furan in products on the Canadian market prompted the authors to conduct a survey of canned and jarred food products. Methyl analogues of furan, 2-methylfuran and 3-methylfuran, were analysed concurrently with furan via a newly developed isotope dilution method, as these analogues were detected in foods in the authors’ earlier work and are likely to undergo a similar metabolic fate as furan itself. The paper reports data on 176 samples, including 17 samples of baby food. The vast majority of samples were packaged in cans or jars. Furan was detected above 1 ng g^?1 in all non-baby food samples with a median of 28 ng g^?1 and concentrations ranging from 1.1 to 1230 ng g^?1. Also, 96% of these samples were found to contain 2-methylfuran above 1 ng g^?1 with a median of 12.8 ng g^?1 and a maximum concentration of 152 ng g^?1, while 81% of samples were found to contain 3-methylfuran above 1 ng g^?1 with a median of 6 ng g^?1 and a maximum concentration of 151 ng g^?1. Similarly, furan was detected above 1 ng g^?1 in all baby food samples with a median of 66.2 ng g^?1 and concentrations ranging from 8.5 to 331 ng g^?1. Also, 100% of these samples were found to contain 2-methylfuran above 1 ng g^?1 with a median of 8.7 ng g^?1 and a maximum concentration of 50.2 ng g^?1, while 65% of samples were found to contain 3-methylfuran above 1 ng g^?1 with a median of 1.6 ng g^?1 and a maximum concentration of 22.9 ng g^?1. Additionally, three coffee samples were analysed ‘as is’, without brewing, and were found to have high levels of furans, especially 2-methylfuran, at a maximum of 8680 ng g^?1. Using this data set, dietary exposures to furan and total furans were calculated. Average furan and total furan intakes by adults (≥20 years) were estimated at approximately 0.37 and 0.71 µg kg^?1 of body weight day^?1 respectively.     

Temperature effects on the removal of potential HFC replacements, CF3CH2CH2OH and CF3(CH2)2CH2OH, initiated by OH radicals

The gas-phase kinetic coefficients of OH radicals with two primary fluorinated alcohols, CF(3)CH(2)CH(2)OH (k(1)) and CF(3)(CH(2))(2)CH(2)OH (k(2)), potential replacements of hydrofluorocarbons (HFCs), are reported here as a function of temperature (T = 263-358 K) for the first time. k(1) and k(2) (together referred as k(i)) were measured under pseudo-first-order conditions with respect to the initial OH concentration using the pulsed laser photolysis/laser induced fluorescence technique. The observed temperature dependence of k(i) (in cm(3) molecule(-1) s(-1)) is described by the following Arrhenius expressions: k(1)(T) = (2.82 ± 1.28) × 10(-12) exp{-(302 ± 139)/T} cm(3) molecule(-1) s(-1) and k(2)(T) = (1.20 ± 0.73) × 10(-11) exp{-(425 ± 188)/T} cm(3) molecule(-1) s(-1).The uncertainties in the Arrhenius parameters are at a 95% confidence level (± 2σ). Uncertainties in k(i)(T) include both statistical and systematic errors. Activation energies were (2.5 ± 1.2) kJ/mol and (3.6 ± 1.6) kJ/mol for the OH-reaction with CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH, respectively. The global lifetime (τ) at 275 K for CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH due to the OH-reaction was estimated to be ca. 2 weeks and 5 days, respectively. The reported Arrhenius parameters can be used in 3D models that take into account the geographical region and season of emissions for estimating a matrix of instantaneous lifetimes. As a consequence of the substitution of the -CH(3) group by a -CH(2)OH group in HFCs, such as CF(3)CH(2)CH(3) and CF(3)(CH(2))(2)CH(3), the tropospheric lifetime with respect to the OH reaction is significantly shorter and, since their radiative forcing is similar, global warming potentials of CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH are negligible. Therefore, CF(3)CH(2)CH(2)OH and CF(3)(CH(2))(2)CH(2)OH seem to be suitable alternatives to HFCs.     

Hydroxyaldehyde products from hydroxyl radical reactions of Z-3-hexen-1-ol and 2-methyl-3-buten-2-ol quantified by SPME and API-MS

Hydroxyaldehyde products of the OH radical-initiated reactions (in the presence of NO) of two volatile vegetative emissions, Z-3-hexen-1-ol and 2-methyl-3-buten-2-ol, were examined to assess the qualitative and quantitative potential of two analysis techniques (1) sampling by Solid-Phase MicroExtraction (SPME) with on-fiber derivatization followed by gas chromatographic analyses and (2) in situ analysis by negative ion mode atmospheric pressure ionization mass spectrometry (API-MS). The compounds were chosen because reaction mechanisms predict hydroxyaldehyde products, and reliable coproduct yield data are available. The API-MS analyses showed product ion peaks attributed to the NO2- adducts of 3-hydroxypropanal and dihydroxynitrates from Z-3-hexen-1-ol, and a formation yield of 3-hydroxypropanal of 44% was derived. Product ion peaks attributed to NO2- adducts of glycolaldehyde [HOCH2CHO], 2-hydroxy-2-methylpropanal [(CH3)2C(OH)CHO], and dihydroxynitrates were observed by API-MS from 2-methyl-3-buten-2-ol, and a formation yield of 2-hydroxy-2-methylpropanal of 16% was obtained. In experiments with SPME sampling, the formation yields of hydroxycarbonyls measured as their oxime derivatives were as follows: from Z-3-hexen-1-ol, propanal, 56 +/- 8%; 3-hydroxypropanal, 101 +/- 24%; and from 2-methyl-3-buten-2-ol, 2-hydroxy-2-methylpropanal, 31 +/- 4%. Both the API-MS and SPME analyses provided product information, and hydroxycarbonyl yields from the SPME data are in reasonable agreement with previously measured formation yields of coproducts.     

Dicarbonyl products of the OH radical-initiated reactions of naphthalene and the Cl- and C2-alkylnaphthalenes

Naphthalene and the C1- and C2-alkylnaphthalenes are the most abundant polycyclic aromatic hydrocarbons (PAHs) in urban atmospheres. Their major atmospheric loss process is by gas-phase reaction with hydroxyl (OH) radicals. In this study, we have used in situ direct air sampling atmospheric pressure ionization mass spectrometry (API-MS) as well as gas chromatography-mass spectrometry (GC/MS) techniques to investigate the products of the gas-phase reactions of OH radicals with naphthalene, naphthalene-ds, 1- and 2-methylnaphthalene (MN), 1- and 2-MN-dio, 1- and 2-ethylnaphthalene (EN), and the 10 isomeric dimethylnaphthalenes (DMNs). The major reaction products are ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two P-carbons and associated alkyl groups, and ring-containing compounds that may be epoxides. Phthalic anhydride and alkyl-substituted phthalic anhydrides were observed as second generation products. The position of alkyl-substitution on the naphthalene ring is a key factor determining the ring cleavage site and the isomeric product distribution.     

Products and mechanism of secondary organic aerosol formation from reactions of n-alkanes with OH radicals in the presence of NOx

Secondary organic aerosol (SOA) formation from reactions of n-alkanes with OH radicals in the presence of NOx was investigated in an environmental chamber using a thermal desorption particle beam mass spectrometer for particle analysis. SOA consisted of both first- and higher-generation products, all of which were nitrates. Major first-generation products were sigma-hydroxynitrates, while higher-generation products consisted of dinitrates, hydroxydinitrates, and substituted tetrahydrofurans containing nitrooxy, hydroxyl, and carbonyl groups. The substituted tetrahydrofurans are formed by a series of reactions in which sigma-hydroxycarbonyls isomerize to cyclic hemiacetals, which then dehydrate to form substituted dihydrofurans (unsaturated compounds) that quickly react with OH radicals to form lower volatility products. SOA yields ranged from approximately 0.5% for C8 to approximately 53% for C15, with a sharp increase from approximately 8% for C11 to approximately 50% for C13. This was probably due to an increase in the contribution of first-generation products, as well as other factors. For example, SOA formed from the C10 reaction contained no first-generation products, while for the C15 reaction SOA was approximately 40% first-generation and approximately 60% higher-generation products, respectively. First-generation sigma-hydroxycarbonyls are especially important in SOA formation, since their subsequent reactions can rapidly form low volatility compounds. In the atmosphere, substituted dihydrofurans created from sigma-hydroxycarbonyls will primarily react with O3 or NO3 radicals, thereby opening reaction pathways not normally accessible to saturated compounds.     

Atmospheric chemistry of 2-ethoxy-3,3,4,4,5-pentafluorotetrahydro-2,5-bis[1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl]-furan: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the title compound which we refer to as RfOC2H5. Rate constants of k(Cl + RfOC2H5) = (2.70 +/- 0.36) x 10(-12), k(OH + RfOC2H5) = (5.93 +/- 0.85) x 10(-14), and k(Cl + RfOCHO) = (1.34 +/- 0.20) x 10(-14) cm3 molecule(-1') s(-1) were measured in 700 Torr of N2, or air, diluent at 294 +/- 1 K. From the value of k(OH + RfOC2H5) the atmospheric lifetime of RfOC2H5 was estimated to be 1 year. Two competing loss mechanisms for RfOCH(O*)CH3 radicals were identified in 700 Torr of N2/O2 diluent at 294 +/- 1 K; decomposition via C-C bond scission giving a formate (RfOCHO), or reaction with 02 giving an acetate (RfOC(O)CH3). In 700 Torr of N2/O2 diluent at 294 +/- 1 K the rate constant ratio k(O2)/k(diss) = (1.26 +/- 0.74) x 10(-19) cm3 molecule(-1). The OH radical initiated atmospheric oxidation of RfOC2H5 gives Rf0CHO and RfOC(O)CH3 as major products. RfOC2H5 has a global warming potential of approximately 55 for a 100 year horizon. The results are discussed with respect to the atmospheric chemistry and environmental impact of RfOC2H5.     

Fluoranthene-2,3- and -1,5-diones are novel products from the bacterial transformation of fluoranthene

Fluoranthene is one of the predominant compounds found in soils and sediments contaminated with polycyclic aromatic hydrocarbons (PAH). Four bacterial strains isolated from PAH-contaminated soils transformed fluoranthene to a number of products during growth on phenanthrene, including the novel metabolites fluoranthene-2,3-dione (F23Q) and fluoranthene-1,5-dione (F15Q). Given the known toxicity and mutagenicity of F23Q, we focused on characterizing this metabolite with respect to its effects on the metabolism of other PAH. The yield of F23Q from fluoranthene ranged from 2% for Sphingomonas yanoikuyae R1 to greater than 20% for Pseudomonas stutzeri P16 and Bacillus cereus P21. None of the strains appeared capable of metabolizing F23Q any further. F23Q strongly inhibited phenanthrene removal by strain R1 but had a negligible to minor effect on phenanthrene degradation by the other organisms. At a concentration of 6.8 microM, F23Q also substantially inhibited the mineralization of benz[a]anthracene, benzo[a]pyrene (BaP), and chrysene by strain R1 as well as BaP mineralization by Pseudomonas saccharophila P15. Inhibition of BaP mineralization by strain P15 was still evident at an F23Q concentration of 0.68 microM. The inhibition of strain R1 by F23Q was explained in part by a cytotoxic effect, but results with strain P15 indicate that other mechanisms of inhibition occur. These findings suggest that quinones such as F23Q and F15Q have the potential to accumulate in PAH-contaminated systems and can inhibit the degradation of other PAH.     

First direct detection of HONO in the reaction of methylnitrite (CH3ONO) with OH radicals

We report on the development of a new environmental simulation chamber coupled with an in situ continuous wave cavity ring-down spectrometer operating in the near IR (～1.5 μm). The first application reported in this paper dealt with the chemical mechanism of UV photolysis of methyl nitrite (CH(3)ONO) in air. HONO has been detected for the first time and shown to be formed in the OH + CH(3)ONO reaction. A dense spectrum of cis-HONO absorption lines has been observed near 1.5 μm, in agreement with a previous study (Guilmot et al.). CH(2)O has been measured as primary product with good sensitivity and time resolution. In contrast to Zhao et al., we did not detect any NO(2) absorption features in this wavelength range. Calibration experiments provided very low NO(2) absorption cross sections in this region (～10(-25) cm(2)), leading to conclude that NO(2) cannot be observed in this wavelength range in the presence of equal amounts of CH(2)O.     

Formation and reaction of hydroxycarbonyls from the reaction of OH radicals with 1,3-butadiene and isoprene

1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are emitted into the atmosphere in vehicle exhaust and, in the case of isoprene, from vegetation. We have investigated the formation and further reaction of products of their hydroxyl radical-initiated reactions using atmospheric pressure ionization mass spectrometry (API-MS) and solid-phase microextraction fibers precoated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for on-fiber derivatization of carbonyl compounds, with subsequent analysis by thermal desorption and gas chromatography with flame ionization detection (SPME/GC-FID) or MS detection. Products attributed as HOCH2CH=CHCHO and HOCH2CH=CHCH2ONO2 (and isomers) from 1,3-butadiene; HOCD2CD=CDCDO and HOCD2CD=CDCD2ONO2 (and isomers) from 1,3-butadiene-d6; HOCH2C(CH3)=CHCHO and/or HOCH2CH=C(CH3)CHO, and HOCH2C(CH3)=CHCH2ONO2 (and isomers) from isoprene; and HOCD2C(CD3)=CDCDO and/or HOCD2CD=C(CD3)CDO, and HOCD2C(CD3)=CDCD2ONO2 (and isomers) from isoprene-d8 were observed as their NO2- adducts in the API-MS analyses. The hydroxycarbonyls were observed from SPME/GC-FID analyses of the 1,3-butadiene and isoprene reactions as their oximes, together with acrolein, glycolaldehyde, and glyoxal from the 1,3-butadiene reaction. A rate constant for the reaction of OH radicals with 4-hydroxy-2-butenal of (5.7 +/- 1.4) x 10(-11) cm3 molecule(-1) s(-1) at 298 +/- 2 K was derived, and formation yields of acrolein and 4-hydroxy-2-butenal from the 1,3-butadiene reaction of 58 +/- 10% and 25 (+15/-10)%, respectively, were determined. Analogous experiments showed that the two C5-hydroxycarbonyls formed from isoprene have rate constants for their reactions with OH radicals of (1.0 +/- 0.3) x 10(-10) cm3 molecule(-1) s(-1) and (4 +/- 2) x 10(-11) cm3 molecule(-1) s(-1) and a combined yield of approximately 15%, although isomer-specific identification of the hydroxycarbonyls was not achieved.     

Products and mechanism of the reaction of OH radicals with 2,2,4-trimethylpentane in the presence of NO

Alkanes are important constituents of gasoline fuel and vehicle exhaust, with branched alkanes comprising a significant fraction of the total alkanes observed in urban areas. Products of the gas-phase reactions of OH radicals with 2,2,4-trimethylpentane and 2,2,4-trimethylpentane-d18 in the presence of NO at 298+/-2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography-mass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). Acetone, 2-methylpropanal, and 4-hydroxy-4-methyl-2-pentanone were identified and quantified by GC-FID from 2,2,4-trimethylpentane with molar formation yields of 54+/-7%, 26+/-3%, and 5.1+/-0.6%, respectively; upper limits to the formation yields of acetaldehyde, 2,2-dimethylpropanal, and 4,4-dimethyl-2-pentanone were obtained. Additional products observed from 2,2,4-trimethylpentane by API-MS and API-MS/MS analyses using positive and negative ion modes were hydroxy products of molecular weight 130 and 144, a product of molecular weight 128 (attributed to a C8-carbonyl), and hydroxynitrates of molecular weight 135, 177, and 191 (attributed to HOC4H8ONO2, HOC7H14ONO2, and HOC8H16-ONO2, respectively). Formation of HOC8H16ONO2 and HOC7H14-ONO2 is consistent with the observation of products of molecular weight 207 (HOC8D16ONO2) and 191 (HOC7D14-ONO2), respectively, in the API-MS analyses of the 2,2,4-trimethylpentane-d18 reaction (-OD groups rapidly exchange to -OH groups under our experimental conditions). These product data allow the reaction pathways to be delineated to a reasonable extent, and the reaction mechanism is discussed.