- Cold-surface photochemistry of selected organic nitrates
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Reflection-absorption infrared (RAIR) spectroscopy has been used to explore the low temperature condensed-phase photochemistry of atmospherically relevant organic nitrates for the first time. Three alkyl nitrates, methyl, isopropyl, and isobutyl nitrate together with a peroxyacyl nitrate, peroxyacetyl nitrate (PAN), were examined. For the alkyl nitrates, similar photolysis products were observed whether they were deposited neat to the gold substrate or codeposited with water. In addition to peaks associated with the formation of an aldehyde/ketone and NO, a peak near 2230 cm-1 was found to emerge in the RAIR spectra upon UV photolysis of the thin films. Together with evidence obtained by thermal programmed desorption (TPD), the peak is attributed to the formation of nitrous oxide, N2O, generated as a product during the photolysis. On the basis of the known gas-phase photochemistry for the alkyl nitrates, an intermediate pathway involving the formation of nitroxyl (HNO) is proposed to lead to the observed N2O photoproduct. For peroxyacetyl nitrate, CO2 was observed as a predominant product upon photolytic decomposition. In addition, RAIR absorptions attributable to the formation of methyl nitrate were also found to appear upon photolysis. By analogy to the known gas-phase and matrix-isolated-phase photochemistry of PAN, the formation of methyl nitrate is shown to likely result from the combination of alkoxy radicals and nitrogen dioxide generated inside the thin films during photolysis.
- O'Sullivan, Daniel,McLaughlin, Ryan P.,Clemitshaw, Kevin C.,Sodeau, John R.
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- Linear-Reactor-IR.-Matrix and Microwave Spectroscopy of the System O3/NO2/(Z)-2-Butene
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Investigation of the formation of complex reaction products in the gas-phase system O3/NO2/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark spectroscopy is reported.Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified: N2O5, HNO3, HNO4, CH3NO2, CH3ONO, CH3COONO2 and CH3COO2NO2 (peroxyacetyl nitrate PAN).Matrix IR spectra of N2O5, HNO3, CH3COONO, CH3COONO2 required for reference purposes are presented.It is shown that PAN-formation occurs already in the absence of light.A reaction scheme is proposed for explanation of the observed complex NOx-containing products, which assumes methyldioxirane as a central intermediate.Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.
- Dommen, Joseph,Forster, Martin,Rupreccht, Heidi,Bauder, Alfred,Guenthard, Hans-Heinrich
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- Kinetic and Theoretical Studies of the Reactions (CH3C(O)O2 + NO2 + M ->/<- CH3C(O)O2NO2 + M between 248 and 393 K and between 30 and 760 Torr
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The kinetics of the thermal decomposition and formation reactions of acetyl peroxynitrate (PAN) CH3C(O)O2 + NO2 + M ->/1 and k-1, the equilibrium constant K1(T) was calculated to be 0.9 x 10-28 exp((14000 +/- 200)/T) cm3 molecule-1.Quantum chemical and RRKM calculations were performed to obtain accurate and predictive representations of the data.In Troe's notation, the RRKM curves corresponding to the experimental results are represented by the following expressions for the limiting low- and high-pressure rate constants, with Fc = 0.30; k0(-1) = 4.9 x 10-3 exp(-(12100 +/- 500)/T) cm3 molecule-1 s-1; kinfinite(-1) = 4.0 x 1016 exp(-(13600 +/- 350)/T) s-1; k0(1) = 2.7 x 10-28(T/298)-7.1 +/- 1.7 cm6 molecule-2 s-1; kinfinite(1) = (12.1 +/- 0.5) x 10-12(T/298)-0.9 +/- 0.15 cm3 molecule-1 s-1.The thermochemistry of reactions 1 and -1 and the atmospheric implications of the thermal stability of PAN are briefly discussed.
- Bridier, I.,Caralp, F.,Loirat, H.,Lesclaux, R.,Veyret, B.,et al.
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- FTIR studies of the NO3 initiated degradation of but-2-yne: Mechanism and rate constant determination
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The products and mechanism of the gas-phase reaction of NO3 radicals with but-2-yne in purified air have been investigated by FTIR spectroscopy. The experiments were carried out at 298 ± 3 K and 760 ± 5 Torr in a 250 1 stainless-steel reactor in which NO3 was generated by the thermal dissociation of N2O5. Experiments with 15NO3 were also performed. Products include butadione, peroxyacetyl nitrate, ketene and acetic acid. Ketene was observed to react further with NO3 and this reaction was also investigated. The rate constants for the NO3 reaction with but-2-yne and ketene were determined by the relative-rate method as 7.0 ± 0.8 and 10.6 + 1.3 × 10-14 cm3 molecule-1 s-1, respectively, using (E)-but-2-ene as a reference. Reaction mechanisms for the but-2-yne and the ketene degradations are proposed.
- Seland, John G.,Noremsaune, Ingse M. W.,Nielsen, Claus J.
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- Formation of nitrogenous compounds in the photooxidation of n-butane under atmospheric conditions
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The photooxidation of n-butane under atmospheric conditions in the presence of NOx resulted in the formation of the following nitrogenous products: peroxy acetyl nitrate 23, sec-butyl nitrate 16, n-butyl nitrate 1.3, ethyl nitrate 1.3, peroxy n-butyryl nitrate 1.3, and peroxy propionyl nitrate 0.5% of the initially added odd nitrogen. In addition, an electron capturing compound eluting at the retention time of sec-propyl nitrate was also observed accounting for 5% of initial NOx. Butan-2-one was the major product of conversion of n-butane with a yield of 37%. From product ratios it is evident that the formation of sec-butyl nitrate is favored over that of n-butyl nitrate by a factor of 2.1. The rate of reaction of sec-butoxy radicals with oxygen is equal to their decomposition rate.
- Evmorfopoulou, Efthalia,Glavas, Sotirios
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- Promotion of the Oxidation of Nitric Oxide and Hydrocarbon by the Thermal Decomposition of Peroxyacetyl Nitrate (PAN) at Night
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The decomposition of PAN in the presence of nitric oxide and propene in the air was investigated at 30 deg C under dark conditions.The number of nitric oxide molecules oxidized per each PAN molecule decomposed varied from 3.7 to above 5 with increase of the ratio of initial concentration of propene to that of nitric oxide.
- Iwamoto, Issei,Tanihara, Hitoshi,Kawahara, Masaaki,Otsuka, Soichi,Sakamoto, Kazuhiko
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- Branching ratios for the reaction of selected carbonyl-containing peroxy radicals with hydroperoxy radicals
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An important chemical sink for organic peroxy radicals (RO2) in the troposphere is reaction with hydroperoxy radicals (HO2). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branching ratios: RO2 + HO2 → ROOH + O2 (R1a), RO 2 + HO2 → ROH + O3 (R1b), RO2 + HO2 → RO + OH + O2 (R1c). Theoretical work suggests that reactions (R1b) and (R1c) may be a general feature of acyl peroxy and α-carbonyl peroxy radicals. In this work, branching ratios for R1a-R1c were derived for six carbonyl-containing peroxy radicals: C2H 5C(O)O2, C3H7C(O)O2, CH3C(O)CH2O2, CH3C(O)CH(O 2)CH3, CH2ClCH(O2)C(O)CH 3, and CH2ClC(CH3)(O2)CHO. Branching ratios for reactions of Cl-atoms with butanal, butanone, methacrolein, and methyl vinyl ketone were also measured as a part of this work. Product yields were determined using a combination of long path Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection, gas chromatography with flame ionization detection, and gas chromatography-mass spectrometry. The following branching ratios were determined: C2H5C(O)O2, YR1a = 0.35 ± 0.1, YR1b = 0.25 ± 0.1, and YR1c = 0.4 ± 0.1; C3H7C(O)O2, YR1a = 0.24 ± 0.15, YR1b = 0.29 ± 0.1, and YR1c = 0.47 ± 0.15; CH3C(O)CH2O2, Y R1a = 0.75 ± 0.13, YR1b = 0, and YR1c = 0.25 ± 0.13; CH3C(O)CH(O2)CH3, Y R1a = 0.42 ± 0.1, YR1b = 0, and YR1c = 0.58 ± 0.1; CH2ClC(CH3)(O2)CHO, Y R1a = 0.2 ± 0.2, YR1b = 0, and YR1c = 0.8 ± 0.2; and CH2ClCH(O2)C(O)CH3, YR1a = 0.2 ± 0.1, YR1b = 0, and YR1c = 0.8 ± 0.2. The results give insights into possible mechanisms for cycling of OH radicals in the atmosphere.
- Hasson, Alam S.,Tyndall, Geoffrey S.,Orlando, John J.,Singh, Sukhdeep,Hernandez, Samuel Q.,Campbell, Sean,Ibarra, Yesenia
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experimental part
p. 6264 - 6281
(2012/08/28)
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- Atmospheric chemistry of two biodiesel model compounds: Methyl propionate and ethyl acetate
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The atmospheric chemistry of two C4H8O2 isomers (methyl propionate and ethyl acetate) was investigated. With relative rate techniques in 980 mbar of air at 293 K the following rate constants were determined: k(C2H5C(O)OCH3 + Cl) = (1.57 ± 0.23) × 10-11, k(C2H5C(O) OCH3 + OH) = (9.25 ± 1.27) × 10-13, k(CH 3C(O)OC2H5 + Cl) = (1.76 ± 0.22) × 10-11, and k(CH3C(O)OC2H5 + OH) = (1.54 ± 0.22) × 10-12 cm3 molecule -1 s-1. The chlorine atom initiated oxidation of methyl propionate in 930 mbar of N2/O2 diluent (with, and without, NOx) gave methyl pyruvate, propionic acid, acetaldehyde, formic acid, and formaldehyde as products. In experiments conducted in N 2 diluent the formation of CH3CHClC(O)OCH3 and CH3CCl2C(O)OCH3 was observed. From the observed product yields we conclude that the branching ratios for reaction of chlorine atoms with the CH3-, -CH2-, and -OCH3 groups are 9 ± 2%, respectively. The chlorine atom initiated oxidation of ethyl acetate in N2/O 2 diluent gave acetic acid, acetic acid anhydride, acetic formic anhydride, formaldehyde, and, in the presence of NOx, PAN. From the yield of these products we conclude that at least 41 ± 6% of the reaction of chlorine atoms with ethyl acetate occurs at the -CH2- group. The rate constants and branching ratios for reactions of OH radicals with methyl propionate and ethyl acetate were investigated theoretically using transition state theory. The stationary points along the oxidation pathways were optimized at the CCSD(T)/cc-pVTZ//BHandHLYP/aug-cc-pVTZ level of theory. The reaction of OH radicals with ethyl acetate was computed to occur essentially exclusively (~99%) at the -CH2- group. In contrast, both methyl groups and the -CH2- group contribute appreciably in the reaction of OH with methyl propionate. Decomposition via the α-ester rearrangement (to give C2H5C(O)OH and a HCO radical) and reaction with O 2 (to give CH3CH2C(O)OC(O)H) are competing atmospheric fates of the alkoxy radical CH3CH2C(O)OCH 2O. Chemical activation of CH3CH2C(O)OCH 2O radicals formed in the reaction of the corresponding peroxy radical with NO favors the α-ester rearrangement.
- Andersen, Vibeke F.,Berhanu, Tesfaye A.,Nilsson, Elna J. K.,Jorgensen, Solvejg,Nielsen, Ole John,Wallington, Timothy J.,Johnson, Matthew S.
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experimental part
p. 8906 - 8919
(2011/10/17)
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- Relative and absolute kinetic studies of 2-butanol and related alcohols with tropospheric Cl atoms
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A newly constructed chamber/Fourier transform infrared system was used to determine the relative rate coefficient, ki, for the gas-phase reaction of Cl atoms with 2-butanol (k1), 2-methyl-2-butanol (k 2), 3-methyl-2-butanol (k3), 2,3-dimethyl-2-butanol (k4) and 2-pentanol (k5). Experiments were performed at (298 ± 2) K, in 740 Torr total pressure of synthetic air, and the measured rate coefficients were, in cm3 molecule-1 s -1 units (±2σ): k1 = (1.32 ± 0.14) × 10-10, k2 = (7.0 ± 2.2) × 10 -11, k3 = (1.17 ± 0.14) × 10-10, k4 = (1.03 ± 0.17) × 10-10 and k5 = (2.18 ± 0.36) × 10-10, respectively. Also, all the above rate coefficients (except for 2-pentanol) were investigated as a function of temperature (267-384 K) by pulsed laser photolysis-resonance fluorescence (PLP-RF). The obtained kinetic data were used to derive the Arrhenius expressions: k1(T) = (6.16 ± 0.58) × 10 -11exp[(174 ± 58)/T], k2(T) = (2.48 ± 0.17) × 10-11exp[(328 ± 42)/T], k3(T) = (6.29 ± 0.57) × 10-11exp[(192 ± 56)/T], and k 4(T) = (4.80 ± 0.43) × 10-11exp[(221 ± 56)/T] (in units of cm3 molecule-1 s-1 and ±σ). Results and mechanism are discussed and compared with the reported reactivity with OH radicals. Some atmospheric implications derived from this study are also reported. This journal is the Owner Societies.
- Ballesteros, Bernabe,Garzon, Andres,Jimenez, Elena,Notario, Alberto,Albaladejo, Jose
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p. 1210 - 1218
(2008/04/05)
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- Atmospheric chemistry of diethyl methylphosphonate, diethyl ethylphosphonate, and triethyl phosphate
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Rate constants for the reactions of OH radicals and NO3 radicals with diethyl methylphosphonate [DEMP, (C2H5O) 2P(O)CH3], diethyl ethylphosphonate [DEEP, (C 2H5O)2P(O)C2H5], and triethyl phosphate [TEP, (C2H5O)3PO] have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained for the OH radical reactions (in units of 10-11 cm3 molecule-1 s-1 were as follows: DEMP, 5.78 ± 0.24; DEEP, 6.45 ± 0.27; and TEP, 5.44 ± 0.20. The rate constants obtained for the NO3 radical reactions (in units of 10-16 cm3 molecule-1 s-1) were the following: DEMP, 3.7 ± 1.1; DEEP, 3.4 ± 1.4; and TEP, 2.4 ± 1.4. For the reactions of O3 with DEMP, DEEP, and TEP, an upper limit to the rate constant of -20 cm3 molecule-1 s-1 was determined for each compound. Products of the reactions of OH radicals with DEMP, DEEP, and TEP were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and, for the TEP reaction, gas chromatography with flame ionization detection (GC-FID) and in situ Fourier transform infrared (FT-IR) spectroscopy. The API-MS analyses show that the reactions are analogous, with formation of one major product from each reaction: C2H5OP(O)(OH)CH3 from DEMP, C 2H5OP(O)(OH)C2H2 from DEEP, and (C2H5O)2P(O)OH from TEP. The FT-IR and GC-FID analyses showed that the major products (and their molar yields) from the TEP reaction are (C2H5O)2P(O)OH (65-82%, initial), CO2 (80 ± 10%), and HCHO (55 ± 5%), together with lesser yields of CH3CHO (11 ± 2%), CO (11 ± 3%), CH3C(O)OONO2 (8%), organic nitrates (7%), and acetates (4%). The probable reaction mechanisms are discussed.
- Aschmann, Sara M.,Tuazon, Ernesto C.,Atkinson, Roger
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p. 2282 - 2291
(2007/10/03)
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- Thermal stability of peroxynitrates
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Peroxynitrates are thermally unstable intermediates (at ambient temperatures) in the atmospheric degradation of hydrocarbons. In this work, thermal lifetimes of nine peroxynitrates have been measured as a function of temperature and, for two of them, also, as a function of total pressure. In the presence of excess NO, relative concentrations of the peroxynitrates were followed in a 420 I reaction chamber as a function of time by means of long-path IR absorption using a Fourier transform spectrometer. Original data on the unimolecular decomposition rate constants are presented for the peroxynitrates RO2NO2 with R = C6H11, CH3C(O)CH2, C6H5CH2, CH2I, CH3C(O)OC(H)CH3, C6H5OCH2, (CH3)2NC(O), C6H5OC(O), and C2H5C(O). Thermal lifetimes at room temperature and atmospheric pressure are very short (in the order of seconds) for substituted methyl peroxynitrates (i.e., R′CH2O2NO2) but rather long for substituted formyl peroxynitrates (i.e., R″C(O)O2NO2). Kinetic data from this and previous work from our laboratory are used to derive structure-stability relationships which allow an estimate of the thermal lifetimes of peroxynitrates from readily available 13C n.m.r. shift data.
- Kirchner,Mayer-Figge,Zabel,Becker
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p. 127 - 144
(2007/10/03)
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- Absolute and relative rate constants for the reactions CH3C(O)O2 + NO and CH3C(O)O2 + NO2 and thermal stability of CH3C(O)O2NO2
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A pulse-radiolysis system was used to measure absolute rate constants for the reactions of CH3C(O)O2 radicals with NO and NO2 at 295 K and 1000 mbar total pressure of SF6. When the rate of formation and decay of NO2 using its absorption at 400.5 and 452 nm were monitored, the rate constants k(CH3C(O)O2 + NO) = (2.0 ± 0.3) × 10-11 and k(CH3C(O)O2 + NO2) = (1.0 ± 0.2) × 10-11 cm3 molecule-1 s-1 were determined. Long path-length Fourier transform infrared spectrometers were used to study the rate-constant ratio k(CH3C-(O)O2 + NO)/k(CH3C(O)O2 + NO2) in 6-700 Torr total pressure of N2 diluent at 243-295 K. At 295 K in 700 Torr of N2 diluent k(CH3C(O)O2 + NO)/k(CH3C(O)O2 + NO2) = 2.07 ± 0.21. The results are discussed in the context of the atmospheric chemistry of acetylperoxy radicals.
- Sehested, Jens,Christensen, Lene Krogh,M?gelberg, Trine,Nielsen, Ole J.,Wallington, Timothy J.,Guschin, Andrei,Orlando, John J.,Tyndall, Geoffrey S.
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p. 1779 - 1789
(2007/10/03)
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- Relative rate study of the reactions of acetylperoxy radicals with NO and NO2: peroxyacetyl nitrate formation under laboratory conditions related to the troposphere
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A relative rate study has been performed on the reactions CH3C(O)O2· + NO2 + M → CH3C(O)O2NO2 + M (1) and CH3C(O)O2· + NO → CH3· + CO2 + NO2 (2) in an atmospheric flow system in which the relative yields of CH3C(O)O2NO2 (PAN) have been measured as a function of the ratio of reactants [NO]/[NO2]. Over the temperature range 247-298 K, at a total pressure of approx.1 atm, the ratio was independent of temperature, k1/k2 = 0.41 ± 0.03, where the error limits are 2σ. The results are discussed with reference to other relative rate measurements of k1/k2 and to absolute measurements of k1 and k2. The atmospheric implications of the ratio k1/k2 in relation to PAN are briefly considered.
- Seefeld,Kinnison,Kerr
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- Temperature-dependent study of the CH3C(O)O2 + NO reaction
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The kinetics of the reaction between acetylperoxy radicals and nitric oxide have been examined both by transient IR absorption and by time-resolved UV spectroscopy. The former technique enables measurements of NO loss and NO2 formation, whereas the latter provides data on the decay of acetylperoxy radicals, the secondary formation of methylperoxy radicals, and their conversion into methylnitrite. The two methods give consistent rate constants which are fit by the expression k1 = (2.1-0.8+1.4) × 10-12e(570±140)/T cm3 s-1. The room temperature value of k1 = (1.4 ± 0.2) × 10-11 cm3 s-1 is somewhat smaller than the currently recommended value, which is based on indirect determinations of k1. Measurements of the CH3O2 and NO2 yields indicate that the reaction proceeds exclusively to the products CH3C(O)O and NO2. The negative temperature dependence suggests that the reaction proceeds via an intermediate adduct that rearranges and dissociates into the products.
- Maricq, M. Matti,Szente, Joseph J.
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p. 12380 - 12385
(2007/10/03)
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- Unimolecular Decomposition of Peroxynitrates
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Thermal decomposition rate constants of peroxynitric acid (HO2NO2) and chloromethyl peroxynitrate (CH2ClO2NO2) were measured as a function of temperature and total pressure in a photochemical reaction chamber of 420 l volume.Peroxynitrate concentrations were monitored by long-path IR absorption using a Fourier transform spectrometer.Analysis of these results in terms of unimolecular reaction rate theories yields kinetic parameters which allow to calculate decomposition rate constants of HO2NO2 and CH2ClO2NO2 for all pressures and temperatures which are of interest for atmospheric applications.These results, together with kinetic data on the thermal decomposition of other peroxynitrates previously obtained in our laboratory, allow to rationalize the change of the bond energies in peroxynitrates (RO2-NO2) with the nature of the group R.Combination of the decomposition data with experimental results on the reverse reactions from the literature are used to determine thermochemical data of peroxynitrates. - Keywords: Peroxynitric acid / Peroxynitrates / Thermal decomposition
- Zabel, F.
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p. 119 - 142
(2007/10/02)
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- Formation and Thermal Decomposition of Butyl-Substituted Peroxyacyl Nitrates: n-C4H9C(O)OONO2 and i-C4H9C(O)OONO2
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The butyl-substituted peroxyacyl nitrates n-C4H9C(O)OONO2 and i-C4H9C(O)OONO2 have been synthesized in the liquid phase, prepared in-situ in the gas phase by sunlight irradiation of aldehyde-NO mixtures, measured by electron capture gas chromatography, and characterized in a number of gas-phase and liquid-phase tests. Gas-phase yields as a fraction of initial NO were 0.39 for the n-butyl isomer and 0.20 for the isobutyl isomer. The corresponding gas-phase aldehyde oxidation mechanisms are outlined. Thermal decomposition in the presence of excess NO yielded n-butanal and isobutanal as the major carbonyl products. Thermal decomposition rates at ambient temperature and atmospheric pressure are comparable to that of PAN , with k298 = 1.8E-4 s-1 for n-C4H9C(O)OONO2 and 2.4E-4 s-1 for i-C4H9C(O)OONO2. Emission data for precursor hydrocarbons indicate C4H9C(O)OONO2/PAN ambient concentration ratios of 0.19 in urban air. Atmospheric implications for the formation and removal of C4H9C(O)OONO2 are briefly discussed.
- Grosjean, Daniel,Grosjean, Eric,Williams, Edwin L.
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p. 1099 - 1105
(2007/10/03)
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- Atmospheric Chemistry of 2-Ethyl Acrolein
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The atmospheric oxidation of the unsaturated aldehyde 2-ethyl acrolein, CH2=C(C2H5)CHO, has been studied in laboratory experiments involving the reaction of ozone with 2-ethyl acrolein in the dark (with cyclohexane added to scavenge the hydroxyl radical), and the sunlight irradiation of 2-ethyl acrolein with NO in air.The major carbonyl products of the 2-ethyl acrolein reaction with ozone are formaldehyde, acetaldehyde, and the dicarbonyl ethylglyoxal, CH3CH2COCHO.Sunlight irradiation of 2-ethyl acrolein and NO led to the formation of three carbonyls (formaldehyde, acetaldehyde, and ethylglyoxal) and three peroxyacyl nitrates, (RC(O)OONO2), including PAN (R = CH3), PPN (R = C2H5, and the unsaturated compound EPAN (R = CH2=C(C2H5).Mechanisms are outlined for the reactions of ozone and of the hydroxyl radical with 2-ethyl acrolein.These mechanisms are consistent with the observed carbonyl and peroxyacyl nitrate products.Thermal decomposition, a major atmospheric removal process for peroxyacyl nitrates, has been studied for EPAN.The decomposition rate of EPAN relative to that of PAN is 0.59-0.73 at 292-294 K and 1 atm of air.Atmospheric implication of these results are discussed.
- Grosjean, Daniel,Grosjean, Eric,Williams, Edwin L.
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p. 365 - 373
(2007/10/02)
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- FTIR Product Study of the Cl-Initiated Oxidation of C2H5Cl: Reactions of the Alkoxy Radical CH3CHClO
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The Cl-atom-initiated oxidation of C2H5Cl has been investigated at 295 K using Fourier transform infrared (FTIR) spectroscopy.The observed products are HCl, CO2, CH3COCl, HCHO, CO, CH3OH, HCOOH, CH3OOH, CH3C(O)OOH, and CH2ClCHO.The yields of HCl and CO2 per C2H5Cl consumed are surprisingly high, (157 +/- 6) percent and (53 +/- 5) percent, and are constant over the C2H5Cl consumption range of 3 - 15 percent.To rationalize these results, we propose a new alkoxy radical decomposition pathway: the CH3CHClO radical intramolecularly eliminates HCl to produce the acetyl radical, CH3CO, which subsequently reacts to form CO2 and methyl radical oxidation products.As part of this work, a relative rate technique was used to measure the reactivity of Cl atoms toward C2H5Cl, CD3CH2Cl, and CH3COCl.We report k(Cl+C2H5Cl) = (8.7 +/- 1.0) x 10-12, k(Cl+CD3CH2Cl) = (7.3 +/- 1.0) x 10-12 and k(Cl+CH3COCl) -14 (units of cm3 molecule-1 s-1).The implications of our results are discussed in terms of understanding the atmospheric chemistry of halogenated organic compounds.
- Shi, Jichun,Wallington, Timothy J.,Kaiser, E. W.
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p. 6184 - 6192
(2007/10/02)
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- Product Quantum Yields for the 350 nm Photodecomposition of Pyruvic Acid in Air
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Quantum yields for the products CH3CHO, CO2 and CH3COOH in the 350 nm photodecomposition of pyruvic acid are 0.48 +/- 0.01, 1.27 +/- 0.18 and 0.14, respectively, as measured in air at atmospheric pressure.In the presence of NO2 the quantum yield for CH3CHO was reduced to 0.30 +/- 0.04 and peroxyacetyl nitrate was formed with a quantum yield of 0.15 +/- 0.02.This is taken to indicate the formation of acetyl radicals in one of the primary processes.Photochemistry / Pyruvic Acid / PAN
- Berges, Markus G. M.,Warneck, Peter
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p. 413 - 416
(2007/10/02)
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- Determination of the Rate Constant Ratio for the Reactions of the Acetylperoxy Radical with NO and NO2
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The thermal decomposition of acetyl peroxynitrate was studied in a 420 l DURAN glass reaction chamber in the presence of different initial / ratios.From an analysis of the rate data, the following rate constant ratios k2/k1 for the reactions of CH3C(O)O2 radicals with NO (k1) and NO2(k2) were derived at different temperatures and total pressures: 0.45 +/- 0.05 (304 K, 1000 mbar), 0.41 +/- 0.05 (321 K, 1000 mbar), 0.42 +/- 0.02 (313 K. 1000 mbar), 0.39 +/- 0.02 (313 K, 300 mbar), 0.28 +/- 0.04 (313 K, 100 mbar), 0.25 +/- 0.04 (313 K, 30 mbar).Using recent data on k2, a pressure independent rate constant k1 = (2.1 +/- 0.5)*10-11 cm3 molecule-1 s-1 was deduced from these ratios at 313 K.
- Kirchner, F.,Zabel, F.,Becker, K. H.
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p. 1379 - 1382
(2007/10/02)
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- Ring-cleavage Reactions of Aromatic Hydrocarbons Studied by FT-IR Spectroscopy. I. Photooxidation of Toluene and Benzene in the NOx-Air System
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The products of the atmospheric photooxidation reactions of toluene and benzene were analyzed quantitatively using long-path FT-IR spectroscopy.Methylglyoxal (only in the case of toluene), glyoxal and maleic acid anhydride were observed as aromatic ring-cleavage products.In the toluene photooxidation, yields of methylglyoxal, glyoxal, and maleic anhydride were 14+/-4, 15+/-4, and 4.0+/-0.4percent (mole/mole), respectively.The formation of small molecules, formaldehyde and formic acid, was observed.It is suggested that the precursor of the ring-cleavage reaction is OH-aromatic-O2 adducts, and that the α-dicarbonyls and unsaturated γ-dicarbonyls are produced by ring cleavage after cyclization of the OH-aromatics-O2 adduct.The observation of maleic anhydride is considered as an evidence of the aromatic ring cleavage into C2 and C4 fragments.The fraction of the ring cleavage process in the total reaction is 29 and 15-20percent in the case of toluene and benzene, respectively.
- Bandow, Hiroshi,Washida, Nobuaki,Akimoto, Hajime
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p. 2531 - 2540
(2007/10/02)
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- The formation of ozone and peroxyacetyl nitrate (PAN) in the urban atmospheres of Alberta
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Atmospheric temperature inversions frequently trap pollutants in the urban atmospheres of Alberta leading to photochemical air pollution.Peroxyacetyl nitrate (PAN) was monitored, for the first time in Alberta, from November 1980 to August 1981 at the University of Calgary using electron capture gas chromatography.Measurements were made at one-half-hour intervals from July, 1981 to February, 1982 at a downtown location.Maximum PAN concentrations were recorded at the University and downtown sites on August 14 at 1400 h, 1981 and values were 2.4 and 6.6 ppb, respectively.In each case the maximum PAN peak coincided with the afternoon peak in ozone concentrations, 79 ppb at the University and 59 ppb at the downtown site.Surprisingly, a high value of 2.3 ppb PAN was recorded at the University during January of 1981 giving rise to questions regarding the influence of low temperatures and solar radiation on the photochemical formation of PAN.Calculations employinga simple photochemical model for PAN and ozone formation have been carried out and comparisons made between the observed and the computed values.
- Peake, E.,Sandhu, H. S.
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p. 927 - 935
(2007/10/02)
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