Atmospheric chemistry of benzyl alcohol: kinetics and mechanism of reaction with OH radicals.

The atmospheric oxidation of benzyl alcohol has been investigated using smog chambers at ICARE, FORD, and EUPHORE. The rate coefficient for reaction with OH radicals was measured and an upper limit for the reaction with ozone was established; kOH = (2.8 ± 0.4) × 10(-11) at 297 ± 3 K (averaged value including results from Harrison and Wells) and kO(3) < 2 × 10(-19) cm(3) molecule(-1) s(-1) at 299 K. The products of the OH radical initiated oxidation of benzyl alcohol in the presence of NOX were studied. Benzaldehyde, originating from H-abstraction from the -CH(2)OH group, was identified using in situ FTIR spectroscopy, HPLC-UV/FID, and GC-PID and quantified in a yield of (24 ± 5) %. Ring retaining products originating from OH-addition to the aromatic ring such as o-hydroxybenzylalcohol and o-dihydroxybenzene as well as ring-cleavage products such as glyoxal were also identified and quantified with molar yields of (22 ± 2)%, (10 ± 3)%, and (2.7 ± 0.7)%, respectively. Formaldehyde was observed with a molar yield of (27 ± 10)%. The results are discussed with respect to previous studies and the atmospheric oxidation mechanism of benzyl alcohol.

Atmospheric degradation of perfluoro-2-methyl-3-pentanone: photolysis, hydrolysis and hydration.

Perfluorinated carboxylic acids are widely distributed in the environment, including remote regions, but their sources are not well understood. Perfluoropropionic acid (PFPrA, CF(3)CF(2)C(O)OH) has been observed in rainwater but the observed amounts can not be explained by currently known degradation pathways. Smog chamber studies were performed to assess the potential of photolysis of perfluoro-2-methyl-3-pentanone (PFMP, CF(3)CF(2)C(O)CF(CF(3))(2)), a commonly used fire-fighting fluid, to contribute to the observed PFPrA loadings. The photolysis of PFMP gives CF(3)CF(2)C·(O) and ·CF(CF(3))(2) radicals. A small (0.6%) but discernible yield of PFPrA was observed in smog chamber experiments by liquid chromatography-mass spectrometry offline chamber samples. The Tropospheric Ultraviolet-Visible (TUV) model was used to estimate an atmospheric lifetime of PFMP with respect to photolysis of 4-14 days depending on latitude and time of year. PFMP can undergo hydrolysis to produce PFPrA and CF(3)CFHCF(3) (HFC-227ea) in a manner analogous to the Haloform reaction. The rate of hydrolysis was measured using (19)F NMR at two different pHs and was too slow to be of importance in the atmosphere. Hydration of PFMP to give a geminal diol was investigated computationally using density functional theory. It was determined that hydration is not an important environmental fate of PFMP. The atmospheric fate of PFMP seems to be direct photolysis which, under low NO(x) conditions, gives PFPrA in a small yield. PFMP degradation contributes to, but does not appear to be the major source of, PFPrA observed in rainwater.

Kinetics and mechanism of chlorine-atom-initiated oxidation of allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol.

The gas-phase reactions of Cl atoms with allyl alcohol (k(1)), 3-buten-2-ol (k(2)), and 2-methyl-3-buten-2-ol (k(3)) at 296 +/- 2 K have been investigated using absolute and relative rate methods in 1-700 Torr of N(2) diluent. Absolute rate studies were performed using pulsed laser photolysis/vacuum ultraviolet laser-induced fluorescence spectroscopy techniques. Relative rate studies were performed using smog chamber/Fourier transform infrared spectroscopy techniques. The absolute and relative rate studies gave consistent results. The kinetics of the reactions are dependent on pressure over the range studied. Molar yields for HCl production in 700 Torr of N(2) for reactions of chlorine atoms with allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol were measured to be 0.26 +/- 0.03, 0.23 +/- 0.03, and 0.12 +/- 0.02, respectively. The chlorine-atom-initiated oxidation of 2-methyl-3-buten-2-ol in 700 Torr of air gave the following products (molar yields): acetone (47 +/- 4%), chloroacetaldehyde (47 +/- 5%), and HCHO (7.2 +/- 0.6%). The observation of substantial and indistinguishable yields of acetone and chloroacetaldehyde products indicates that a major fraction of the reaction proceeds via addition of chlorine atoms to the terminal carbon atom. The results are discussed with respect to the literature data.

CHF2OCHF2 (HFE-134): IR spectrum and kinetics and products of the chlorine-atom-initiated oxidation.

Smog chamber/FTIR techniques were used to measure k(Cl + CHF(2)OCHF(2)) = (5.7 +/- 1.5) x 10(-16) cm(3) molecule(-1) s(-1) in 700 Torr of N(2)/O(2) diluent at 296 +/- 1 K. This result is 100 times lower than the previous literature value. The chlorine-atom-initiated atmospheric oxidation of CHF(2)OCHF(2) gives COF(2) in a molar yield of (185 +/- 22) %. The IR spectrum was recorded, and a radiative efficiency of 0.44 W m(-2) ppb(-1) was determined. The results are discussed with respect to the atmospheric chemistry and environmental impact of CHF(2)OCHF(2).

Atmospheric chemistry of 4:2 fluorotelomer acrylate [C4F9CH2CH2OC(O)CH=CH2]: kinetics, mechanisms, and products of chlorine-atom- and OH-radical-initiated oxidation.

Relative rate techniques were used to measure the rate constants k[Cl + C(4)F(9)CH(2)CH(2)OC(O)CH=CH(2)] = (2.21 +/- 0.16) x 10(-10) and k[OH + C(4)F(9)CH(2)CH(2)OC(O)CH=CH(2)] = (1.13 +/- 0.12) x 10(-11) cm(3) molecule(-1) s(-1) in 700 Torr of N(2) or air diluent at 296 K. The atmospheric lifetime of C(4)F(9)CH(2)CH(2)OC(O)CHCH(2) (4:2 FTAc) is determined by its reaction with OH radicals and is approximately 1 day. The chlorine-atom-initiated oxidation of 4:2 FTAc in 700 Torr of air at 296 K gives C(4)F(9)CH(2)C(O)H in molar yields of 18% and 10% in the absence and presence of NO, respectively. The OH-radical-initiated oxidation of 4:2 FTAc in 700 Torr of air in the presence of NO gives HCHO in a molar yield of (102 +/- 7)%, with C(4)F(9)CH(2)CH(2)OC(O)C(O)H (4:2 fluorotelomer glyoxylate) as the expected coproduct. The atmospheric fate of the 4:2 fluorotelomer glyoxylate will be photolysis and reaction with OH radicals, which will lead to the formation of C(4)F(9)CH(2)C(O)H and ultimately perfluorinated carboxylic acids. The atmospheric oxidation of fluorotelomer acrylates is a potential source of perfluorinated carboxylic acids in remote locations.

Atmospheric chemistry of 4:2 fluorotelomer iodide (n-C4F9CH2CH2I): kinetics and products of photolysis and reaction with OH radicals and Cl atoms.

Relative rate techniques were used to study the title reactions and determine rate constants of k(Cl + C(4)F(9)CH(2)CH(2)I) = (1.25 +/- 0.15) x 10(-12) and k(OH + C(4)F(9)CH(2)CH(2)I) = (1.2 +/- 0.6) x 10(-12) cm(3) molecule(-1) s(-1) in 700 Torr total pressure at 295 K. The fluorotelomer aldehyde (C(4)F(9)CH(2)CHO), perfluorinated aldehyde (C(4)F(9)CHO), fluorotelomer acid (C(4)F(9)CH(2)C(O)OH), fluorotelomer peracid (C(4)F(9)CH(2)C(O)OOH), and several perfluorocarboxylic acids were detected by in situ FTIR spectroscopy and offline analysis as products of the chlorine atom initiated oxidation of C(4)F(9)CH(2)CH(2)I in air. The UV-visible spectra of C(4)F(9)CH(2)CH(2)I and C(2)H(5)Cl were recorded over the range of 200-400 nm. Photolysis of C(4)F(9)CH(2)CH(2)I gives C(4)F(9)CH(2)CHO as the major observed product. By assumption of a photolysis quantum yield of unity, it was calculated that the atmospheric lifetime of C(4)F(9)CH(2)CH(2)I is determined by photolysis and is a few days. A mechanism for the atmospheric oxidation of fluorotelomer iodides, (C(x)F(2x+1)CH(2)CH(2)I, where x = 2, 4, 6,...) is proposed. Atmospheric oxidation of fluorotelomer iodides is a potential source of perfluorocarboxylic acids.

Paint solvent to food additive: an environmental route of dehalogenation for 4-chlorobenzotrifluoride.

In an effort to reduce volatile organic compounds (VOCs) in paint solvents, replacements containing non-VOC compounds have been proposed. One such compound is 4-chlorobenzotrifluoride (CBTF), for which environmental fate studies have not been conducted. The objective of the present study was to determine the products of the atmospheric oxidation of CBTF and the aqueous fate of these products. Smog chamber experiments were performed to measure the kinetics and mechanism of atmospheric oxidation. A rate constant of 2.22 (+/-0.30) x 10(-13) cm3 molecule(-1) s(-1) was determined for the reaction of hydroxyl radicals with CBTF in 700 Torr of air at 296 K. Using offline sampling and gas chromatography coupled to mass spectroscopic analysis, it was determined that 2-chloro-5-trifluoromethylphenol (o-CTFP) was the primary product of CBTF atmospheric oxidation. Aqueous photolysis of o-CTFP in deionized water proceeded at a rate of 1.3 (+/-0.1) x 10(-4) s(-1), corresponding to a half-life of 1.5 +/- 0.1 h and a quantum yield of 6.6 (+/-0.4) x 10(-4). The mechanism of photolysis was investigated using liquid chromatography coupled to tandem mass spectrometry, which suggested that degradation of o-CTFP occurred via photonucleophilic displacement of chlorine, followed by photoinduced hydrolysis of the trifluoromethyl group to yield 3,4-dihydroxybenzoic acid (an approved food additive considered to be nontoxic).

Atmospheric chemistry of perfluoroaldehydes (CxF2x+1CHO) and fluorotelomer aldehydes (CxF2x+1CH2CHO): quantification of the important role of photolysis.

The UV absorption spectra of CF(3)CHO, C(2)F(5)CHO, C(3)F(7)CHO, C(4)F(9)CHO, CF(3)CH(2)CHO, and C(6)F(13)CH(2)CHO were recorded over the range 225-400 nm at 249-297 K. C(x)F(2)(x)(+1)CHO and C(x)F(2)(x)(+1)CH(2)CHO have broad absorption features centered at 300-310 and 290-300 nm, respectively. The strength of the absorption increases with the size of the C(x)F(2)(x)(+1) group. There was no discernible (<5%) effect of temperature on the UV spectra. Quantum yields for photolysis at 254 and 308 nm were measured. Quantum yields at 254 nm were 0.79 +/- 0.09 (CF(3)CHO), 0.81 +/- 0.09 (C(2)F(5)CHO), 0.63 +/- 0.09 (C(3)F(7)CHO), 0.60 +/- 0.09 (C(4)F(9)CHO), 0.74 +/- 0.08 (CF(3)CH(2)CHO), and 0.55 +/- 0.09 (C(6)F(13)CH(2)CHO). Quantum yields at 308 nm were 0.17 +/- 0.03 (CF(3)CHO), 0.08 +/- 0.02 (C(4)F(9)CHO), and 0.04 +/- 0.01 (CF(3)CH(2)CHO). The quantum yields decrease with increasing size of the C(x)F(2)(x)(+1) group and with increasing wavelength of the photolysis light. The photolysis quantum yield at 308 nm for CF(3)CHO measured here is a factor of at least 8 greater than that reported previously. Photolysis is probably the dominant atmospheric fate of C(x)F(2)(x)(+1)CHO (x = 1-4) and is an important fate of C(x)F(2)(x)(+1)CH(2)CHO (x = 1 and 6). These results have important ramifications concerning the yield of perfluorocarboxylic acids in the atmospheric oxidation of fluorotelomer alcohols.

Atmospheric lifetime and global warming potential of a perfluoropolyether.

Perfluoropolyethers (PFPEs) are a family of perfluorinated fluids used mainly in industrial applications. Lower molecular weight commercial PFPE fractions have boiling points ranging between 55 and 270 degrees C, and have the potential to escape into the atmosphere. To improve our understanding of the atmospheric chemistry of PFPEs, a distilled fraction of a commercial mixture containing perfluoropolymethylisopropyl ethers (PFPMIEs) was introduced into an atmospheric chamber system. Relative rate techniques were used to determine upper limits for the rate constants for reactions of OH and Cl with PFPMIE in 700 Torr of air at 296 K. The reactivity of PFPMIE with Cl was less than 2 x 10(-17) cm3 molecule(-1) s(-1), while the reactivity with OH was less than 6.8 x 10(-16) cm3 molecule(-1) s(-1), indicating low reactivity in the troposphere. Consequently, the lifetime of PFPMIE should be limited bytransport to the mesosphere, where photolysis by Lyman-alpha radiation at 121.6 nm will be efficient. By analogy to perfluorinated alkanes, the lower limit for the total atmospheric lifetime is 800 years. PFPMIE was shown to have instantaneous radiative forcing of 0.65 W m(-2) ppb(-1), which corresponds to a global warming potential on a 100 year time scale of 9000 relative to CO2 and 1.95 relative to CFC-11.

Atmospheric chemistry of N-methyl perfluorobutane sulfonamidoethanol, C4F9SO2N(CH3)CH2CH2OH: kinetics and mechanism of reaction with OH.

Relative rate methods were used to measure the gas-phase reaction of N-methyl perfluorobutane sulfonamidoethanol (NMeFBSE) with OH radicals, giving k(OH + NMeFBSE) = (5.8 +/- 0.8) x 10(-12) cm3 molecule(-1) s(-1) in 750 Torr of air diluent at 296 K. The atmospheric lifetime of NMeFBSE is determined by reaction with OH radicals and is approximately 2 days. Degradation products were identified by in situ FTIR spectroscopy and offline GC-MS and LC-MS/MS analysis. The primary carbonyl product C4F9SO2N(CH3)CH2CHO, N-methyl perfluorobutane sulfonamide (C4F9SO2NH(CH3)), perfluorobutanoic acid (C3F7C(O)OH), perfluoropropanoic acid (C2F5C(O)OH), trifluoroacetic acid (CF3C(O)OH), carbonyl fluoride (COF2), and perfluorobutane sulfonic acid (C4F9SO3H) were identified as products. A mechanism involving the addition of OH to the sulfone double bond was proposed to explain the production of perfluorobutane sulfonic acid and perfluorinated carboxylic acids in yields of 1 and 10%, respectively. The gas-phase N-dealkylation product, N-methyl perfluorobutane sulfonamide (NMeFBSA), has an atmospheric lifetime (>20 days) which is much longer than that of the parent compound, NMeFBSE. Accordingly,the production of NMeFBSA exposes a mechanism by which NMeFBSE may contribute to the burden of perfluorinated contamination in remote locations despite its relatively short atmospheric lifetime. Using the atmospheric fate of NMeFBSE as a guide, it appears that anthropogenic production of N-methyl perfluorooctane sulfonamidoethanol (NMeFOSE) contributes to the ubiquity of perfluoroalkyl sulfonate and carboxylate compounds in the environment.

Atmospheric chemistry of CH3CHF2 (HFC-152a): kinetics, mechanisms, and products of Cl atom- and OH radical-initiated oxidation in the presence and absence of NO(x).

Smog chamber/Fourier transform infrared (FTIR) and laser-induced fluorescence (LIF) spectroscopic techniques were used to study the atmospheric degradation of CH3CHF2. The kinetics and products of the Cl(2P(3/2)) (denoted Cl) atom- and the OH radical-initiated oxidation of CH3CHF2 in 700 Torr of air or N2; diluents at 295 +/- 2 K were studied using smog chamber/FTIR techniques. Relative rate methods were used to measure k(Cl + CH3CHF2) = (2.37 +/- 0.31) x 10(-13) and k(OH + CH3CHF2) = (3.08 +/- 0.62) x 10(-14) cm3 molecule(-1) s(-1). Reaction with Cl atoms gives CH3CF2 radicals in a yield of 99.2 +/- 0.1% and CH2CHF2 radicals in a yield of 0.8 +/- 0.1%. Reaction with OH radicals gives CH3CF2 radicals in a yield >75% and CH2CHF2 radicals in a yield <25%. Absolute rate data for the Cl reaction were measured using quantum-state selective LIF detection of Cl(2P(j)) atoms under pseudo-first-order conditions. The rate constant k(Cl + CH3CHF2) was determined to be (2.54 +/- 0.25) x 10(-13) cm3 molecule(-1) s(-1) by the LIF technique, in good agreement with the relative rate results. The removal rate of spin-orbit excited-state Cl(2P(1/2)) (denoted Cl) in collisions with CH3CHF2 was determined to be k(Cl + CH3CHF2) = (2.21 +/- 0.22) x 10(-10) cm3 molecule(-1) s(-1). The atmospheric photooxidation products were examined in the presence and absence of NO(x). In the absence of NO(x)(), the Cl atom-initiated oxidation of CH3CHF2 in air leads to formation of COF2 in a molar yield of 97 +/- 5%. In the presence of NO(x), the observed oxidation products include COF2 and CH3COF. As [NO] increases, the yield of COF2 decreases while the yield of CH3COF increases, reflecting a competition for CH3CF2O radicals. The simplest explanation for the observed dependence of the CH3COF yield on [NO(x)] is that the atmospheric degradation of CH3CF2H proceeds via OH radical attack to give CH3CF2 radicals which add O2 to give CH3CF2O2 radicals. Reaction of CH3CF2O2 radicals with NO gives a substantial fraction of chemically activated alkoxy radicals, [CH3CF2O]. In 1 atm of air, approximately 30% of the alkoxy radicals produced in the CH3CF2O2 + NO reaction possess sufficient internal excitation to undergo "prompt" (rate >10(10) s(-1)) decomposition to give CH3 radicals and COF2. The remaining approximately 70% become thermalized, CH3CF2O, and undergo decomposition more slowly at a rate of approximately 2 x 10(3) s(-1). At high concentrations (>50 mTorr), NO(x) is an efficient scavenger for CH3CF2O radicals leading to the formation of CH3COF and FNO.

Atmospheric chemistry of propionaldehyde: kinetics and mechanisms of reactions with OH radicals and Cl atoms, UV spectrum, and self-reaction kinetics of CH3CH2C(O)O2 radicals at 298 K.

The kinetics and mechanism of the reactions of Cl atoms and OH radicals with CH3CH2CHO were investigated at room temperature using two complementary techniques: flash photolysis/UV absorption and continuous photolysis/FTIR smog chamber. Reaction with Cl atoms proceeds predominantly by abstraction of the aldehydic hydrogen atom to form acyl radicals. FTIR measurements indicated that the acyl forming channel accounts for (88 +/- 5)%, while UV measurements indicated that the acyl forming channel accounts for (88 +/- 3)%. Relative rate methods were used to measure: k(Cl + CH3CH2CHO) = (1.20 +/- 0.23) x 10(-10); k(OH + CH3CH2CHO) = (1.82 +/- 0.23) x 10(-11); and k(Cl + CH3CH2C(O)Cl) = (1.64 +/- 0.22) x 10(-12) cm3 molecule(-1) s(-1). The UV spectrum of CH3CH2C(O)O2, rate constant for self-reaction, and rate constant for cross-reaction with CH3CH2O2 were determined: sigma(207 nm) = (6.71 +/- 0.19) x 10(-18) cm2 molecule(-1), k(CH3CH2C(O)O2 + CH3CH2C(O)O2) = (1.68 +/- 0.08) x 10(-11), and k(CH3CH2C(O)O2 + CH3CH2O2) = (1.20 +/- 0.06) x 10(-11) cm3 molecule(-1) s(-1), where quoted uncertainties only represent 2sigma statistical errors. The infrared spectrum of C2H5C(O)O2NO2 was recorded, and products of the Cl-initiated oxidation of CH3CH2CHO in the presence of O2 with, and without, NO(x) were identified. Results are discussed with respect to the atmospheric chemistry of propionaldehyde.

Atmospheric chemistry of CF3CH2CH2OH: kinetics, mechanisms and products of Cl atom and OH radical initiated oxidation in the presence and absence of NOX.

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with CF(3)CH(2)C(O)H and CF(3)CH(2)CH(2)OH in 700 Torr of N(2) or air diluent at 296 +/- 2 K. The rate constants determined were k(Cl+CF(3)CH(2)C(O)H) = (1.81 +/- 0.27) x 10(-11), k(OH+CF(3)CH(2)C(O)H) = (2.57 +/- 0.44) x 10(-12), k(Cl+CF(3)CH(2)CH(2)OH) = (1.59 +/- 0.20) x 10(-11), and k(OH+CF(3)CH(2)CH(2)OH) = (6.91 +/- 0.91) x 10(-13) cm(3) molecule(-1) s(-1). Product studies of the chlorine initiated oxidation of CF(3)CH(2)CH(2)OH in the absence of NO show the sole primary product to be CF(3)CH(2)C(O)H. Product studies of the chlorine initiated oxidation of CF(3)CH(2)CH(2)OH in the presence of NO show the primary products to be CF(3)CH(2)C(O)H (81%), HC(O)OH (10%), and CF(3)C(O)H. Product studies of the chlorine initiated oxidation of CF(3)CH(2)C(O)H in the absence of NO show the primary products to be CF(3)C(O)H (76%), CF(3)CH(2)C(O)OH (14%), and CF(3)CH(2)C(O)OOH (< or =10%). As part of this work, an upper limit of k(O(3)+CF(3)CH(2)CH(2)OH) < 2 x 10(-21) cm(3) molecule(-1) s(-1) was established. Results are discussed with respect to the atmospheric chemistry of fluorinated alcohols.

Degradation of fluorotelomer alcohols: a likely atmospheric source of perfluorinated carboxylic acids.

Human and animal tissues collected in urban and remote global locations contain persistent and bioaccumulative perfluorinated carboxylic acids (PFCAs). The source of PFCAs was previously unknown. Here we present smog chamber studies that indicate fluorotelomer alcohols (FTOHs) can degrade in the atmosphere to yield a homologous series of PFCAs. Atmospheric degradation of FTOHs is likely to contribute to the widespread dissemination of PFCAs. After their bioaccumulation potential is accounted for, the pattern of PFCAs yielded from FTOHs could account for the distinct contamination profile of PFCAs observed in arctic animals. Furthermore, polar bear liver was shown to contain predominately linear isomers (>99%) of perfluorononanoic acid (PFNA), while both branched and linear isomers were observed for perfluorooctanoic acid, strongly suggesting a sole input of PFNA from "telomer"-based products. The significance of the gas-phase peroxy radical cross reactions that produce PFCAs has not been recognized previously. Such reactions are expected to occur during the atmospheric degradation of all polyfluorinated materials, necessitating a reexamination of the environmental fate and impact of this important class of industrial chemicals.