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1.
Environ Sci Process Impacts ; 22(6): 1347-1354, 2020 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-32356541

RESUMO

An investigation of CCl3COCl was conducted with the purpose of using the compound as an alternative Cl atom precursor in laboratory settings. CCl3COCl can be used with or without O2 as a source of Cl atoms and photolysis studies in air and N2 diluent displayed COCl2 and CO as being the major photolysis products. Relative rate studies were performed to determine the Cl atom rate coefficients for reaction with CH3Cl and C2H2 and the results were in agreement with literature values. Cl atom rate coefficients for reaction with n-CH2[double bond, length as m-dash]CH(CH2)3CN and n-CH2[double bond, length as m-dash]CH(CH2)4CN were determined as (2.95 ± 0.58) × 10-10 and (3.73 ± 0.60) × 10-10 cm3 molecule-1 s-1, respectively. CCl3COCl requires UV-C irradiation, so not all molecules are feasible for use in e.g. relative rate studies. Furthermore, it is recommended to perform experiments with O2 present, as this minimizes IR feature disturbance from product formation.

2.
Environ Sci Process Impacts ; 22(4): 1037-1044, 2020 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-32119021

RESUMO

We have characterized the various pathways for OH radical (OH˙) induced decomposition of tert-butyl methyl ether (MTBE) and found an oxidative pathway that leads to complete degradation under the prerequisite that OH radicals are present in excess. A simple polarizable continuum model is used to predict the behavior in an aqueous medium and the behavior is unchanged compared to that in the gas phase. The computational study has also revealed some of the fundamental aspects of hydrogen transfer from asymmetric ethers; the ˙OH assisted hydrogen abstraction has a barrier when the reaction takes place at a distance from the heteroatom, that is, at the tert-butyl group, whereas hydrogen abstraction from the methyl group proceeds without a barrier. The addition of ˙OH to (CH3)3COCH2˙ also proceeds without a barrier, and so does hydrogen abstraction from the resulting adduct ((CH3)3COCH2OH) to form (CH3)3COCH(OH)˙. However, a barrier is yet again found in the hydrogen abstraction from the latter to form (CH3)3COCH[double bond, length as m-dash]O and yet again in the formation of the formyl radical (CH3)3COC[double bond, length as m-dash]O˙ by hydrogen abstraction. The latter is the last step before the final stage of complete oxidation of MTBE to form CO2.

3.
J Phys Chem A ; 123(47): 10315-10322, 2019 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-31665882

RESUMO

Fourier transform infrared smog chamber techniques were used to study the kinetics and mechanisms of the reactions of Cl atoms and OH radicals with pentafluorophenol (C6F5OH) in 700 Torr total pressure of air or N2 diluent at 296 ± 2 K. Rate constants k(OH + C6F5OH) = (6.88 ± 1.37) × 10-12 cm3 molecule-1 s-1 and k(Cl + C6F5OH) = (2.52 ± 0.31) × 10-11 cm3 s-1 molecule-1 in 700 Torr air diluent were determined. In 700 Torr N2, the rate constant for the reaction of C6F5OH with Cl atoms is linearly dependent on the Cl atom concentration. Product studies on this reaction in both 700 Torr air and 700 Torr N2 diluent show the formation of nonconjugated products. The photolysis constant of C6F5OH was determined by 254 nm UV irradiation of a C6F5OH and CH3CHO mixture in 700 Torr air or N2 at 296 ± 2 K and yielded a photolysis rate constant of J(C6F5OH) = (2.83 ± 0.25) × 10-3 s-1. Results are discussed with respect to the atmospheric chemistry of other halogenated aromatic species.

4.
J Agric Food Chem ; 67(6): 1638-1646, 2019 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-30698961

RESUMO

Neonicotinoids (NN), first introduced in 1991, are found on environmental surfaces where they undergo photolytic degradation. Photolysis studies of thin films of NN were performed using two approaches: (1) transmission FTIR, in which solid films of NN and the gas-phase products were analyzed simultaneously, and (2) attenuated-total-reflectance FTIR combined with transmission FTIR, in which solid films of NN and the gas-phase products were probed in the same experiment but not at the same time. Photolysis quantum yields using broadband irradiation centered at 313 nm were (2.2 ± 0.9) × 10-3 for clothianidin (CLD), (3.9 ± 0.3) × 10-3 for thiamethoxam (TMX), and (3.3 ± 0.5) × 10-3 for dinotefuran (DNF), with all errors being ±1 s. At 254 nm, which was used to gain insight into the wavelength dependence, quantum yields were in the range of (0.8-20) × 10-3 for all NNs, including acetamiprid (ACM) and thiacloprid (TCD). Nitrous oxide (N2O), a potent greenhouse gas, was the only gas-phase product detected for the photolysis of nitroguanidines, with yields of ΔN2O/ΔNN > 0.5 in air at both 313 and 254 nm. The atmospheric lifetimes with respect to photolysis for CLD, TMX, and DNF, which absorb light in the actinic region, are estimated to be 15, 10, and 11 h, respectively, at a solar zenith angle of 35° and 12, 8, and 10 h at a solar zenith angle of 15°.


Assuntos
Inseticidas/química , Neonicotinoides/química , Óxido Nitroso/química , Fotólise/efeitos da radiação , Espectroscopia de Infravermelho com Transformada de Fourier , Luz Solar
5.
Phys Chem Chem Phys ; 21(3): 1497-1505, 2019 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-30608069

RESUMO

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2 or air diluent at 296 ± 2 K. Values of k(Cl + 1-trifluoromethyl-1,2,2-trifluorocyclobutane (TFMTFCB)) = (1.16 ± 0.21) × 10-14 and k(OH + TFMTFCB) = (3.51 ± 0.88) × 10-14 cm3 molecule-1 s-1 were measured. No reactivity of TFMTFCB towards ozone was observed. The atmospheric lifetime of TFMTFCB is determined by the reaction with OH and is approximately 330 days. The chlorine initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (92 ± 2)% and (89 ± 2)%, respectively. The OH radical initiated oxidation gives C(O)F2 and CF3C(O)F as the dominant products in yields of (91 ± 6)% and (84 ± 4)%, respectively. The GWP100 was calculated as 44. The atmospheric chemistry of the title compound, a cyclic halogenated alkane, is discussed in the context of other halogenated cyclo-alkanes.

6.
Phys Chem Chem Phys ; 20(44): 27949-27958, 2018 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-30382259

RESUMO

The chemical mechanisms of the OH radical, Cl-atom and O3 initiated oxidation of (Z)-CF3CH[double bond, length as m-dash]CHCl were studied at 296 ± 1 K in 10-700 Torr air of N2/O2 diluent. Cl atoms add to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] double bond: 12 ± 5% to the terminal carbon and 85 ± 5% to the central carbon. In 700 Torr of air the products are CF3CHClCHO, HCOCl, CF3COCl, CF3CHO, (E)-CF3CH[double bond, length as m-dash]CHCl, CF3C(O)CHCl2, and CF3CHClCOCl. The yield of (E) isomer was dependent on total pressure, but independent of O2 partial pressure; consistent with isomerization occurring via Cl atom elimination from the chemically activated rather than the thermalized CF3CHCHCl-Cl adduct. The rate constant for (Z)-CF3CH[double bond, length as m-dash]CHCl + Cl was measured at low pressure (10-15 Torr) and found to be indistinguishable from that determined at 700 Torr total pressure, whereas the low pressure rate constant for (E)-CF3CH[double bond, length as m-dash]CHCl was 36% smaller. G4MP2 ab initio calculations showed that the (E) isomer is 1.2 kcal mol-1 more stable than the (Z) isomer. Cl atom elimination from the adduct will preferentially form the (E) isomer and hence the rate of CF3CH[double bond, length as m-dash]CHCl loss will be more sensitive to pressure for the (Z) than the (E) isomer. Reaction of (Z)-CF3CH[double bond, length as m-dash]CHCl with OH radicals gives CF3CHO, HCOCl, (E)-CF3CH[double bond, length as m-dash]CHCl, and HCl. A significant chlorine atom elimination channel was observed experimentally, and supported by computational results. The oxidation products of the reaction of O3 with (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl were determined with no evidence of isomerization. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH[double bond, length as m-dash]CHCl.

7.
Phys Chem Chem Phys ; 20(45): 28796-28809, 2018 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-30418435

RESUMO

Photochemical reactors were used to study the kinetics and mechanisms of reactions of Cl atoms and OH radicals with hexa- and penta-fluorobenzene (C6F6, C6F5H) in 700 Torr total pressure of N2, air, or O2 diluent at 296 ± 2 K. C6F6 and C6F5H undergo ring-opening following 254 nm UV irradiation, but with small quantum yields (φ < 0.03). Reaction of Cl atoms with C6F6 proceeds via adduct formation, while the reaction of Cl atoms with C6F5H proceeds via hydrogen abstraction and adduct formation. C6F6-Cl and C6F5H-Cl adducts decompose rapidly (k ∼ 105-106 s-1) reforming the reactants, and react with Cl atoms to form products. The fraction of adduct reacting with Cl atoms increases with steady state Cl atom concentration, resulting in an increasing apparent effective Cl atom rate constant. The rate constant for the H-abstraction channel for Cl + C6F5H is estimated at (7.3 ± 5.7) × 10-16 cm3 molecule-1 s-1. Establishment of the equilibrium between the adducts and the aromatic reactant + Cl occurs rapidly with equilibrium constants of K([adduct]/[aromatic][Cl]) = (1.96 ± 0.11) × 10-16 and (9.28 ± 0.11) × 10-17 cm3 molecule-1 for C6F6 and C6F5H, respectively. Reaction of the adducts with O2 occurs slowly with estimated rate constants of <7 and <4 × 10-18 cm3 molecule-1 s-1 for C6F6-Cl and C6F5H-Cl, respectively. The rate constants for reaction of OH radicals with C6F6 and C6F5H were determined to be (2.27 ± 0.49) × 10-13 and (2.56 ± 0.62) × 10-13 cm3 molecule-1 s-1, respectively. UV and IR spectra of C6F6 and C6F5H at 296 ± 1 K were collected and calibrated. Results are discussed in the context of available literature data for reactions of Cl atoms and OH radicals with halogenated aromatic compounds.

8.
J Phys Chem A ; 122(28): 5983-5992, 2018 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-29924602

RESUMO

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of n-CH2═CH(CH2) xCN ( x = 0-4) with Cl atoms, OH radicals, and O3: k(CH2═CHCN + Cl) = (1.03 ± 0.13) × 10-10, k(CH2═CHCH2CN + Cl) = (2.02 ± 0.35) × 10-10, k(CH2═CH(CH2)2CN + Cl) = (2.75 ± 0.45) × 10-10, k(CH2═CHCN + OH) = (4.21 ± 0.95) × 10-12, k(CH2═CHCH2CN + OH) = (1.55 ± 0.34) × 10-11, k(CH2═CH(CH2)2CN + OH) = (2.98 ± 0.64) × 10-11, k(CH2═CH(CH2)3CN + OH) = (3.34 ± 0.64) × 10-11, k(CH2═CH(CH2)4CN + OH) = (3.61 ± 0.85) × 10-11, k(CH2═CHCN + O3) = (2.55 ± 0.28) × 10-20, k(CH2═CHCH2CN + O3) = (1.17 ± 0.24) × 10-18, k(CH2═CH(CH2)2CN + O3) = (3.35 ± 0.69) × 10-18, k(CH2═CH(CH2)3CN + O3) = (4.07 ± 0.82) × 10-18, and k(CH2═CH(CH2)4CN + O3) = (7.13 ± 1.49) × 10-18 cm3 molecule-1 s-1 at a total pressure of 700 Torr of air or N2 diluents at 296 ± 2 K. CH2ClC(O)CN, HC(O)CN, HC(O)Cl, HCN, NCC(O)OONO2, and ClC(O)OONO2 were identified as products from the Cl initiated oxidation of CH2═CHCN. The product spectra were compared to experimental and theoretically calculated IR spectra. No products could be determined from the oxidation of n-CH2═CH(CH2) xCN ( x = 1-4). With the determined OH rate constants, the atmospheric lifetimes for n-CH2═CH(CH2) xCN ( x = 0-4) were estimated to be 66, 18, 9.3, 8.3, and 7.7 h, respectively. It was found that these unsaturated nitriles have no significant atmospheric environmental impact.

9.
Nature ; 544(7648): 35, 2017 04 05.
Artigo em Inglês | MEDLINE | ID: mdl-28382984
10.
Environ Sci Technol ; 51(3): 1321-1329, 2017 02 07.
Artigo em Inglês | MEDLINE | ID: mdl-27936633

RESUMO

FTIR/smog chamber experiments and ab initio quantum calculations were performed to investigate the atmospheric chemistry of (CF3)2CFCN, a proposed replacement compound for the industrially important sulfur hexafluoride, SF6. The present study determined k(Cl + (CF3)2CFCN) = (2.33 ± 0.87) × 10-17, k(OH + (CF3)2CFCN) = (1.45 ± 0.25) × 10-15, and k(O3 + (CF3)2CFCN) ≤ 6 × 10-24 cm3 molecule-1 s-1, respectively, in 700 Torr of N2 or air diluent at 296 ± 2 K. The main atmospheric sink for (CF3)2CFCN was determined to be reaction with OH radicals. Quantum chemistry calculations, supported by experimental evidence, shows that the (CF3)2CFCN + OH reaction proceeds via OH addition to -C(≡N), followed by O2 addition to -C(OH)═N·, internal H-shift, and OH regeneration. The sole atmospheric degradation products of (CF3)2CFCN appear to be NO, COF2, and CF3C(O)F. The atmospheric lifetime of (CF3)2CFCN is approximately 22 years. The integrated cross section (650-1500 cm-1) for (CF3)2CFCN is (2.22 ± 0.11) × 10-16 cm2 molecule-1 cm-1 which results in a radiative efficiency of 0.217 W m-2 ppb-1. The 100-year Global Warming Potential (GWP) for (CF3)2CFCN was calculated as 1490, a factor of 15 less than that of SF6.


Assuntos
Cloro/química , Radical Hidroxila/química , Aquecimento Global
11.
Phys Chem Chem Phys ; 19(1): 735-750, 2016 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-27929159

RESUMO

The atmospheric fates of Z- and E-CF3CH[double bond, length as m-dash]CHCF3 have been studied, investigating the kinetics and the products of the reactions of the two compounds with Cl atoms, OH radicals, OD radicals, and O3. FTIR smog chamber experiments measured: k(Cl + Z-CF3CH[double bond, length as m-dash]CHCF3) = (2.59 ± 0.47) × 10-11, k(Cl + E-CF3CH[double bond, length as m-dash]CHCF3) = (1.36 ± 0.27) × 10-11, k(OH + Z-CF3CH[double bond, length as m-dash]CHCF3) = (4.21 ± 0.62) × 10-13, k(OH + E-CF3CH[double bond, length as m-dash]CHCF3) = (1.72 ± 0.42) × 10-13, k(OD + Z-CF3CH[double bond, length as m-dash]CHCF3) = (6.94 ± 1.25) × 10-13, k(OD + E-CF3CH[double bond, length as m-dash]CHCF3) = (5.61 ± 0.98) × 10-13, k(O3 + Z-CF3CH[double bond, length as m-dash]CHCF3) = (6.25 ± 0.70) × 10-22, and k(O3 + E-CF3CH[double bond, length as m-dash]CHCF3) = (4.14 ± 0.42) × 10-22 cm3 molecule-1 s-1 in 700 Torr of air/N2/O2 diluents at 296 ± 2 K. E-CF3CH[double bond, length as m-dash]CHCF3 reacts with Cl atoms to give CF3CHClC(O)CF3 in a yield indistinguishable from 100%. Z-CF3CH[double bond, length as m-dash]CHCF3 reacts with Cl atoms to give (95 ± 10)% CF3CHClC(O)CF3 and (7 ± 1)% E-CF3CH[double bond, length as m-dash]CHCF3. CF3CHClC(O)CF3 reacts with Cl atoms to give the secondary product CF3C(O)Cl in a yield indistinguishable from 100%, with the observed co-products C(O)F2 and CF3O3CF3. The main atmospheric fate for Z- and E-CF3CH[double bond, length as m-dash]CHCF3 is reaction with OH radicals. The atmospheric lifetimes of Z- and E-CF3CH[double bond, length as m-dash]CHCF3 are estimated as 27 and 67 days, respectively. IR absorption cross sections are reported and the global warming potentials (GWPs) of Z- and E-CF3CH[double bond, length as m-dash]CHCF3 for the 100 year time horizon are calculated to be GWP100 = 2 and 7, respectively. This study provides a comprehensive description of the atmospheric fate and impact of Z- and E-CF3CH[double bond, length as m-dash]CHCF3.

13.
J Phys Chem A ; 120(37): 7320-6, 2016 Sep 22.
Artigo em Inglês | MEDLINE | ID: mdl-27556743

RESUMO

FTIR smog chamber techniques were used to study the kinetics of the gas-phase reactions of Cl atoms, OD radicals, and O3 with the five-membered ring-structured compounds tetrahydrofuran (C4H8O, THF), 2-methyltetrahydrofuran (CH3C4H7O, 2-MTHF), 2,5-dimethyltetrahydrofuran ((CH3)2C4H5O, 2,5-DMTHF), and furan (C4H4O). The rate coefficients determined using relative rate methods were kTHF+Cl = (1.96 ± 0.24) × 10(-10), kTHF+OD = (1.81 ± 0.27) × 10(-11), kTHF+O3 = (6.41 ± 2.90) × 10(-21), k2-MTHF+Cl = (2.65 ± 0.43) × 10(-10), k2-MTHF+OD = (2.41 ± 0.51) × 10(-11), k2-MTHF+O3 = (1.87 ± 0.82) × 10(-20), k2,5-DMTHF+OD = (4.56 ± 0.68) × 10(-11), k2,5-DMTHF+Cl = (2.84 ± 0.34) × 10(-10), k2,5-DMTHF+O3 = (4.58 ± 2.18), kfuran+Cl = (2.39 ± 0.27) × 10(-10), and kfuran+O3 = (2.60 ± 0.31) × 10(-18) molecules cm(-3) s(-1). Rate coefficients of the reactions with ozone were also determined using the absolute rate method under pseudo-first-order conditions. OD radicals, in place of OH radicals, were produced from CD3ONO to avoid spectral overlap of isopropyl and methyl nitrite with the reactants. The kinetics of OD radical reactions are expected to resemble the kinetics of OH radical reactions, and the rate coefficients of the reactions with OD radicals were used to calculate the atmospheric lifetimes with respect to reactions with OH radicals. The lifetimes of THF, 2-MTHF, and 2,5-DMTHF are approximately 15, 12, and 6 h, respectively.

14.
J Phys Chem A ; 119(42): 10540-52, 2015 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-26439469

RESUMO

Smog chambers with in situ FTIR detection were used to measure rate coefficients in 700 Torr of air and 296 ± 2 K of: k(Cl+(CF3)2CHOCH3) = (5.41 ± 1.63) × 10(-12), k(Cl+(CF3)2CHOCHO) = (9.44 ± 1.81) × 10(-15), k(Cl+CF3C(O)OCH3) = (6.28 ± 0.98) × 10(-14), k(OH+(CF3)2CHOCH3) = (1.86 ± 0.41) × 10(-13), and k(OH+(CF3)2CHOCHO) = (2.08 ± 0.63) × 10(-14) cm(3) molecule(-1) s(-1). The Cl atom initiated oxidation of (CF3)2CHOCH3 gives (CF3)2CHOCHO in a yield indistinguishable from 100%. The OH radical initiated oxidation of (CF3)2CHOCH3 gives the following products (molar yields): (CF3)2CHOCHO (76 ± 8)%, CF3C(O)OCH3 (16 ± 2)%, CF3C(O)CF3 (4 ± 1)%, and C(O)F2 (45 ± 5)%. The primary oxidation product (CF3)2CHOCHO reacts with Cl atoms to give secondary products (molar yields): CF3C(O)CF3 (67 ± 7)%, CF3C(O)OCHO (28 ± 3)%, and C(O)F2 (118 ± 12)%. CF3C(O)OCH3 reacts with Cl atoms to give: CF3C(O)OCHO (80 ± 8)% and C(O)F2 (6 ± 1)%. Atmospheric lifetimes of (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 were estimated to be 62 days, 1.5 years, and 220 days, respectively. The 100-year global warming potentials (GWPs) for (CF3)2CHOCH3, (CF3)2CHOCHO, and CF3C(O)OCH3 are estimated to be 6, 121, and 46, respectively. A comprehensive description of the atmospheric fate of (CF3)2CHOCH3 is presented.

15.
J Phys Chem A ; 116(21): 5164-79, 2012 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-22524192

RESUMO

Ethyl propionate is a model for fatty acid ethyl esters used as first-generation biodiesel. The atmospheric chemistry of ethyl propionate was investigated at 980 mbar total pressure. Relative rate measurements in 980 mbar N(2) at 293 ± 0.5 K were used to determine rate constants of k(C(2)H(5)C(O)OC(2)H(5) + Cl) = (3.11 ± 0.35) × 10(-11), k(CH(3)CHClC(O)OC(2)H(5) + Cl) = (7.43 ± 0.83) × 10(-12), and k(C(2)H(5)C(O)OC(2)H(5) + OH) = (2.14 ± 0.21) × 10(-12) cm(3) molecule(-1) s(-1). At 273-313 K, a negative Arrhenius activation energy of -3 kJ mol(-1) is observed.. The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar N(2) gave the following products (stoichiometric yields): ClCH(2)CH(2)C(O)OC(2)H(5) (0.204 ± 0.031), CH(3)CHClC(O)OC(2)H(5) (0.251 ± 0.040), and C(2)H(5)C(O)OCHClCH(3) (0.481 ± 0.088). The chlorine atom-initiated oxidation of ethyl propionate in 980 mbar of N(2)/O(2) (with and without NO(x)) gave the following products: ethyl pyruvate (CH(3)C(O)C(O)OC(2)H(5)), propionic acid (C(2)H(5)C(O)OH), formaldehyde (HCHO), and, in the presence of NO(x), PAN (CH(3)C(O)OONO(2)). The lack of acetaldehyde as a product suggests that the CH(3)CH(O)C(O)OC(2)H(5) radical favors isomerization over decomposition. From the observed product yields, we conclude that H-abstraction by chlorine atoms from ethyl propionate occurs 20.4 ± 3.1%, 25.1 ± 4.0%, and 48.1 ± 8.8% from the CH(3)-, -CH(2)-, and -OCH(2)- groups, respectively. The rate constant and branching ratios for the reaction between ethyl propionate and the OH radical were investigated theoretically using quantum mechanical calculations and transition state theory. The stationary points along the reaction path were optimized using the CCSD(T)-F12/VDZ-F12//BH&HLYP/aug-cc-pVTZ level of theory; this model showed that OH radicals abstract hydrogen atoms primarily from the -OCH(2)- group (80%).


Assuntos
Atmosfera/química , Propionatos/química , Acetatos/química , Cloro/química , Ésteres , Modelos Moleculares , Conformação Molecular , Óxido Nítrico/química , Nitrogênio/química , Oxigênio/química
16.
J Phys Chem A ; 115(32): 8906-19, 2011 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-21797203

RESUMO

The atmospheric chemistry of two C(4)H(8)O(2) 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(C(2)H(5)C(O)OCH(3) + Cl) = (1.57 ± 0.23) × 10(-11), k(C(2)H(5)C(O)OCH(3) + OH) = (9.25 ± 1.27) × 10(-13), k(CH(3)C(O)OC(2)H(5) + Cl) = (1.76 ± 0.22) × 10(-11), and k(CH(3)C(O)OC(2)H(5) + OH) = (1.54 ± 0.22) × 10(-12) cm(3) molecule(-1) s(-1). The chlorine atom initiated oxidation of methyl propionate in 930 mbar of N(2)/O(2) diluent (with, and without, NO(x)) gave methyl pyruvate, propionic acid, acetaldehyde, formic acid, and formaldehyde as products. In experiments conducted in N(2) diluent the formation of CH(3)CHClC(O)OCH(3) and CH(3)CCl(2)C(O)OCH(3) was observed. From the observed product yields we conclude that the branching ratios for reaction of chlorine atoms with the CH(3)-, -CH(2)-, and -OCH(3) groups are <49 ± 9%, 42 ± 7%, and >9 ± 2%, respectively. The chlorine atom initiated oxidation of ethyl acetate in N(2)/O(2) diluent gave acetic acid, acetic acid anhydride, acetic formic anhydride, formaldehyde, and, in the presence of NO(x), 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 -CH(2)- 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 -CH(2)- group. In contrast, both methyl groups and the -CH(2)- group contribute appreciably in the reaction of OH with methyl propionate. Decomposition via the α-ester rearrangement (to give C(2)H(5)C(O)OH and a HCO radical) and reaction with O(2) (to give CH(3)CH(2)C(O)OC(O)H) are competing atmospheric fates of the alkoxy radical CH(3)CH(2)C(O)OCH(2)O. Chemical activation of CH(3)CH(2)C(O)OCH(2)O radicals formed in the reaction of the corresponding peroxy radical with NO favors the α-ester rearrangement.


Assuntos
Acetatos/química , Atmosfera/química , Biocombustíveis , Cloro/química , Radical Hidroxila/química , Compostos Orgânicos/química , Propionatos/química , Simulação por Computador , Ésteres/química , Cinética , Óxido Nítrico , Oxirredução , Oxigênio , Espectrofotometria Infravermelho
17.
J Phys Chem A ; 115(17): 4388-96, 2011 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-21462920

RESUMO

The solubility of gas-phase acetic acid (CH(3)COOH, HAc) and trifluoroacetic acid (CF(3)COOH, TFA) in aqueous sulfuric acid solutions was measured in a Knudsen cell reactor over ranges of temperature (207-245 K) and acid composition (40-75 wt %, H(2)SO(4)). For both HAc and TFA, the effective Henry's law coefficient, H*, is inversely dependent on temperature. Measured values of H* for TFA range from 1.7 × 10(3) M atm(-1) in 75.0 wt % H(2)SO(4) at 242.5 K to 3.6 × 10(8) M atm(-1) in 40.7 wt % H(2)SO(4) at 207.8 K. Measured values of H* for HAc range from 2.2 × 10(5) M atm(-1) in 57.8 wt % H(2)SO(4) at 245.0 K to 3.8 × 10(8) M atm(-1) in 74.4 wt % H(2)SO(4) at 219.6 K. The solubility of HAc increases with increasing H(2)SO(4) concentration and is higher in strong sulfuric acid than in water. In contrast, the solubility of TFA decreases with increasing sulfuric acid concentration. The equilibrium concentration of HAc in UT/LS aerosol particles is estimated from our measurements and is found to be up to several orders of magnitude higher than those determined for common alcohols and small carbonyl compounds. On the basis of our measured solubility, we determine that HAc in the upper troposphere undergoes aerosol partitioning, though the role of H(2)SO(4) aerosol particles as a sink for HAc in the upper troposphere and lower stratosphere will only be discernible under high atmospheric sulfate perturbations.


Assuntos
Ácido Acético/química , Ácidos Sulfúricos/química , Temperatura , Ácido Trifluoracético/química , Atmosfera , Solubilidade , Soluções
18.
Chemosphere ; 55(7): 1005-25, 2004 May.
Artigo em Inglês | MEDLINE | ID: mdl-15051370

RESUMO

In 1997 a Pollutant Release and Transfer Register (PRTR) pilot project was initiated in Japan. In 1998 the project was expanded and in 1999 a law concerning the establishment of a national PRTR was adopted. Data on the emissions of chemical substances are therefore now being reported on a continuous base. In relation to the PRTR project data on toxicity have been collected. In order to make efficient use of the collected information on emission and toxicity it is useful to group or rank the chemical substances according to the impact on human health and the environment. It has recently been argued that partial order theory (POT) in combination with the use of linear extensions (LE) may be the most objective way to create a linear rank. The methodology has been further expanded to handle larger data sets by the use of random linear extensions (RLE). In this paper the Japanese PRTR data are ranked using the POT/RLE methodology. An average rank is established for chemical substances in the 1998 and 1999 PRTR in Japan. The top 10 chemical substances in the 1998 PRTR are: dichlorvos, inorganic arsenic compounds, cobalt compounds, beryllium compounds, fenitrothion, disulfoton, parathion, diazinon, 4,4'-diamino-3,3'-dichlorodiphenylmethane and antimony compounds. The top 10 chemical substances from the 1999 PRTR are PCBs, lead compounds, fenitrothion, dichlorvos, disulfoton, inorganic arsenic compounds, chlorothalonil, thiobencarb, chromium and HCFC-141b. The descriptor having the highest influence on the ranking of the 1998 PRTR data is the production volume, which, however, is not given in the 1999 PRTR. Further, the disagreement between the ranking with the lack of toxicity data substituted with mean and maximum values, respectively, strongly indicates a general need for further toxicological investigations.


Assuntos
Monitoramento Ambiental/legislação & jurisprudência , Poluentes Ambientais/classificação , Poluentes Ambientais/toxicidade , Sistema de Registros , Interpretação Estatística de Dados , Japão , Medição de Risco
20.
Chemosphere ; 49(6): 637-49, 2002 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-12430651

RESUMO

The combined monitoring-based and modelling-based priority setting scheme (COMMPS) used to establish a priority setting list within the EU Water Framework Directive plays a major role in the European environmental policy on chemical substances. The COMMPS procedure can be classified as a so-called scoring method. The applied functional relationship and weight factors are established based on expert judgement, which unfortunately appears to be vulnerable to subjective inputs. In this study an alternative priority setting methods based on partial order theory (POT) and random linear extensions (RLE) is suggested and compared to the COMMPS procedure. The POT/RLE is characterised as being based on fewer assumptions concerning functional relationships and does not apply weighting factors. Using the POT/RLE methodology a different ranking result occur than when using the COMMPS procedure. Eight of the top 20 substances from the COMMPS procedure are not ranked within the top 20 when using POT/RLE. From the viewpoint of environmental protection, especially the substances that have been given low priority in the COMMPS procedure, but a high rank in POT/RLE, are of interest in a regulatory context. These substances are naphthalene, trichloromethane, isoproturon, metolachlor, endosulfan, acenaphthene, alachlor and dichloromethane. An analysis of the ability of the descriptors to separate the single substance discloses that the most significant descriptor is the concentrations detected in the environment. Further, the frequency of detection is not applied as a descriptor in the COMMPS procedure. However, if this descriptor was to be applied the analysis revealed that it would have been the third most significant descriptor.


Assuntos
Meio Ambiente , Modelos Químicos , Compostos Orgânicos/efeitos adversos , Compostos Orgânicos/química , Poluentes Químicos da Água/efeitos adversos , Algoritmos , Simulação por Computador , Modelos Lineares , Análise de Regressão , Medição de Risco
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