scholarly journals Consecutive reactions of aromatic–OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

2006 ◽  
Vol 6 (4) ◽  
pp. 7623-7656 ◽  
Author(s):  
R. Koch ◽  
R. Knispel ◽  
M. Elend ◽  
M. Siese ◽  
C. Zetzsch
Keyword(s):  
Reaction Mechanism ◽  
Flash Photolysis ◽  
Effective Rate Constant ◽  
Effective Rate ◽  
Atmospheric Composition ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Resonance Fluorescence ◽  
Consecutive Reactions ◽  
Benzene Toluene

Abstract. Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O2, NO and NO2 have been studied for benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s−1, typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O2 or NO, and triexponential decays were obtained in the presence of NO2. The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable. In addition, smog chamber experiments at O2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and p-xylene. The drop of the effective rate constant of removal by OH occurs at reasonable O2 levels, given the FP/RF results. Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O2 predominates over that with NO2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O2.

scholarly journals Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

2007 ◽  
Vol 7 (8) ◽  
pp. 2057-2071 ◽  
Author(s):  
R. Koch ◽  
R. Knispel ◽  
M. Elend ◽  
M. Siese ◽  
C. Zetzsch
Keyword(s):  
Reaction Mechanism ◽  
Flash Photolysis ◽  
Effective Rate Constant ◽  
Effective Rate ◽  
Atmospheric Composition ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Resonance Fluorescence ◽  
Consecutive Reactions ◽  
Benzene Toluene

Abstract. Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O2, NO and NO2 have been studied for benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s−1, typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O2 or NO, and triexponential decays were obtained in the presence of NO2. The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable. In addition, smog chamber experiments at O2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and p-xylene. The drop of the effective rate constant of removal by OH occurs at reasonable O2 levels, given the FP/RF results. Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O2 predominates over that with NO2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O2.

scholarly journals Burning of olive tree branches: a major organic aerosol source in the Mediterranean

2013 ◽  
Vol 13 (17) ◽  
pp. 8797-8811 ◽  
Author(s):  
E. Kostenidou ◽  
C. Kaltsonoudis ◽  
M. Tsiflikiotou ◽  
E. Louvaris ◽  
L. M. Russell ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Olive Tree ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Chemical Aging ◽  
Mediterranean Countries ◽  
Fine Aerosol ◽  
Benzene Toluene ◽  
Ambient Measurements

Abstract. Aerosol produced during the burning of olive tree branches was characterized with both direct source sampling (using a mobile smog chamber) and with ambient measurements during the burning season. The fresh particles were composed of 80% organic matter, 8–10% black carbon (BC), 5% potassium, 3–4% sulfate, 2–3% nitrate and 0.8% chloride. Almost half of the fresh olive tree branches burning organic aerosol (otBB-OA) consisted of alkane groups. Their mode diameter was close to 70 nm. The oxygen to carbon (O : C) ratio of the fresh otBB-OA was 0.29 ± 0.04. The mass fraction of levoglucosan in PM1 was 0.034–0.043, relatively low in comparison with most fuel types. This may lead to an underestimation of the otBB-OA contribution if levoglucosan is being used as a wood burning tracer. Chemical aging was observed during smog chamber experiments, as f44 and O : C ratio increased, due to reactions with OH radicals and O3. The otBB-OA AMS mass spectrum differs from the other published biomass burning spectra, with a main difference at m/z 60, used as levoglucosan tracer. In addition to particles, volatile organic compounds (VOCs) such as methanol, acetonitrile, acrolein, benzene, toluene and xylenes are also emitted. Positive matrix factorization (PMF) was applied to the ambient organic aerosol data and 3 factors could be identified: OOA (oxygenated organic aerosol, 55%), HOA (hydrocarbon-like organic aerosol, 11.3%) and otBB-OA 33.7%. The fresh chamber otBB-OA AMS spectrum is close to the PMF otBB-OA spectrum and resembles the ambient mass spectrum during olive tree branches burning periods. We estimated an otBB-OA emission factor of 3.5 ± 0.9 g kg−1. Assuming that half of the olive tree branches pruned is burned in Greece, 2300 ± 600 tons of otBB-OA are emitted every year. This activity is one of the most important fine aerosol sources during the winter months in Mediterranean countries.

scholarly journals Oxidation reaction mechanism and kinetics between OH radicals and alkyl-substituted aliphatic thiols: OH-addition pathways

2019 ◽  
Vol 44 (2) ◽  
pp. 157-174 ◽  
Author(s):  
Arezoo Tahan ◽  
Abolfazl Shiroudi
Keyword(s):  
Reaction Mechanism ◽  
Rate Constants ◽  
Effective Rate ◽  
Activation Energies ◽  
State Theory ◽  
Rate Coefficients ◽  
Oh Radicals ◽  
Oxidation Reactions ◽  
Kinetic Rate ◽  
Kinetic Rate Constants

Kinetic rate constants for the oxidation reactions of OH radicals with CH3SH (1), C2H5SH (2), n-C3H7SH (3) and iso-C3H7SH (4) under inert conditions (Ar) over the temperature range 252−430 K have been studied using the CBS-QB3 composite method. Kinetic rate constants under atmospheric pressure and in the fall-off regime have been estimated using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Comparison with experiment confirms that in the OH-addition pathways 1−4 leading to the related products, the first bimolecular reaction step has effective negative activation energies around −2.61 to 3.70 kcal mol−1. Effective rate coefficients have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a result of the negative activation energies, pressures larger than 104 bar would be required to restore to some extent the validity of this approximation for all the channels. By comparison with experimental data, all our calculations for both the OH-addition and H-abstraction reaction pathways indicate that from a kinetic viewpoint and in line with the computed reaction energy barriers, the most favourable process is the OH-addition pathway to n-C3H7SH to yield the [ n-C3H7SH−OH]• species, whereas under thermodynamic control of the bimolecular reactions (R−SH+OH•), the most abundant product derived from the H-abstraction pathway will be the [ n-C3H7 S•+H2O] species.

scholarly journals Burning of olive tree branches: a major organic aerosol source in the Mediterranean

2013 ◽  
Vol 13 (3) ◽  
pp. 7223-7266 ◽  
Author(s):  
E. Kostenidou ◽  
C. Kaltsonoudis ◽  
M. Tsiflikiotou ◽  
E. Louvaris ◽  
L. M. Russell ◽  
...  
Keyword(s):  
Mass Spectrum ◽  
Olive Tree ◽  
Organic Aerosol ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Chemical Aging ◽  
Mediterranean Countries ◽  
Fine Aerosol ◽  
Benzene Toluene ◽  
The Mediterranean

Abstract. Aerosol produced during the burning of olive tree branches was characterized with both direct source-sampling (using a mobile smog chamber) and with ambient measurements during the burning season. The fresh particles were composed of 80% organic matter, 8–10% black carbon (BC), 5% potassium, 3–4% sulfate, 2–3% nitrate and 0.8% chloride. Almost half of the fresh olive tree branches burning organic aerosol (otBB-OA) consisted of alkane groups. Their mode diameter was close to 70 nm. The oxygen to carbon (O:C) ratio of the fresh otBB-OA was 0.29 ± 0.04. The mass fraction of levoglucosan in PM1 was 0.034–0.043, relatively low in comparison with most fuel types. This may lead to an underestimation of the otBB-OA contribution if levoglucosan is being used as a wood burning tracer. Chemical aging was observed during smog chamber experiments, as f44 and O:C ratio increased, due to reactions with OH radicals and O3. The otBB-OA AMS mass spectrum differs from the other published biomass burning spectra, with a main difference at m/z 60, used as levoglucosan tracer. In addition to particles, volatile organic compounds (VOCs) such as methanol, acetonitrile, acrolein, benzene, toluene and xylenes are also emitted. Positive matrix factorization (PMF) was applied to the ambient organic aerosol data and 3 factors could be identified: OOA (oxygenated organic aerosol, 55%), HOA (hydrocarbon-like organic aerosol, 11.3%) and otBB-OA 33.7%. The fresh chamber otBB-OA AMS spectrum is close to the PMF otBB-OA spectrum and resembles the ambient mass spectrum during olive tree branches burning periods. We estimated an otBB-OA emission factor of 3.5 ± 0.2 g kg−1. Assuming that half of the olive tree branches pruned is burned in Greece 2280 ± 140 tons of otBB-OA are emitted every year. This activity is one of the most important fine aerosol sources during the winter months in the Mediterranean countries.

scholarly journals Rate Constants for the Reaction of OH Radicals with Hydrocarbons in a Smog Chamber at Low Atmospheric Temperatures

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 320 ◽  
Author(s):  
Lei Han ◽  
Frank Siekmann ◽  
Cornelius Zetzsch
Keyword(s):  
Rate Constants ◽  
Photochemical Reaction ◽  
Relative Rate ◽  
Photochemical Reactions ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Straight Chain ◽  
Atmospheric Lifetime ◽  
Benzene Toluene ◽  
Good Agreement

The photochemical reaction of OH radicals with the 17 hydrocarbons n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, cyclooctane, 2,2-dimethylbutane, 2,2-dimethylpentane, 2,2-dimethylhexane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, benzene, toluene, ethylbenzene, p-xylene, and o-xylene was investigated at 288 and 248 K in a temperature controlled smog chamber. The rate constants were determined from relative rate calculations with toluene and n-pentane as reference compounds, respectively. The results from this work at 288 K show good agreement with previous literature data for the straight-chain hydrocarbons, as well as for cyclooctane, 2,2-dimethylbutane, 2,2,4-trimethylpentane, 2,2,3,3-tetramethylbutane, benzene, and toluene, indicating a convenient method to study the reaction of OH radicals with many hydrocarbons simultaneously. The data at 248 K (k in units of 10−12 cm3 s−1) for 2,2-dimethylpentane (2.97 ± 0.08), 2,2-dimethylhexane (4.30 ± 0.12), 2,2,4-trimethylpentane (3.20 ± 0.11), and ethylbenzene (7.51 ± 0.53) extend the available data range of experiments. Results from this work are useful to evaluate the atmospheric lifetime of the hydrocarbons and are essential for modeling the photochemical reactions of hydrocarbons in the real troposphere.

Oxidation reaction mechanism and kinetics between OH radicals and alkyl-substituted aliphatic thiols: H-abstraction pathways

2019 ◽  
Vol 45 ◽  
pp. 146867831988612
Author(s):  
Arezoo Tahan ◽  
Abolfazl Shiroudi
Keyword(s):  
Reaction Mechanism ◽  
Rate Constants ◽  
Oxidation Reaction ◽  
Density Functional ◽  
Effective Rate ◽  
Bimolecular Reaction ◽  
State Theory ◽  
Oh Radicals ◽  
Step Model ◽  
Kinetic Rate Constants

Kinetic rate constants for the oxidation reaction of the hydroxyl radical with CH3SH, C2H5SH, n-C3H7SH, and iso-C3H7SH under inert (Ar) conditions over the temperature range 252–430 K have been studied theoretically using density functional theory along with various exchange–correlation functionals as well as the benchmark CBS-QB3 quantum chemical approach. Bimolecular rate constants were estimated using transition state theory and the statistical Rice–Ramsperger–Kassel–Marcus theory. Comparison with experiment confirms that in the OH addition reaction pathways leading to the related products, the first bimolecular reaction steps have effective negative activation energy barriers. Effective rate constants have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a consequence of the negative activation energies, pressures higher than 104 bar are required to reach the high-pressure limit. Both from thermodynamic and kinetic viewpoints, the most favorable process here is the oxidation reaction of hydroxyl radicals with n-C3H7SH.

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