Absolute rate constants for F + CH3CHO and CH3CO + O2, relative rate study of CH3CO + NO, and the product distribution of the F + CH3CHO reaction

Sehested, Jens; Christensen, Linda; Nielsen, Ole John; Wallington, Timothy J.

doi:10.1002/(sici)1097-4601(1998)30:12<913::aid-kin6>3.0.co;2-5

Cited by 29 publications

(8 citation statements)

References 28 publications

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“…We have been unsuccessful in finding a CH 3 CO source that does not involve acetaldehyde and yet is suitable for the purpose of DF kinetic studies. The experimental 15,16,27,28 and theoretical 29 rate constants reported for the overall reaction CH 3 CO + O 2 (1) are in accordance with each other, and they appear to define a sigmoidal-type k 1 vs. P pressure-dependence curve. In the low-pressure region (1.3-5 mbar He), McDade et al have determined k 1 (298 K) = (2.0 AE 0.4) Â 10 À12 cm 3 molecule À1 s À1 by using the flash photolysis technique with direct monitoring of CH 3 CO by photoionisation mass spectrometry.…”

Section: Kinetics Of the Overall Reaction Of Ch 3 Co With Osupporting

confidence: 75%

“…The parameter estimations have returned rate constants for the overall reaction CH 3 CO + O 2 (1) in good agreement with data reported from other laboratories. 15,27,28 The fitting procedures have also provided OH yields as a function of pressure. Since no absolute OH concentrations were measured in the experiments by Blitz et al, the yields they report are relative values and are given normalised to the lowest-pressure OH yield in their paper.…”

Section: Oh Yield For the Reaction Of Ch 3 C(o) With Omentioning

confidence: 99%

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Kinetics and mechanism of the reactions of CH3CO and CH3C(O)CH2 radicals with O2. Low-pressure discharge flow experiments and quantum chemical computations

Kovács

Zádor

Farkas

et al. 2007

Phys. Chem. Chem. Phys.

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The reactions CH(3)CO + O(2)--> products (1), CH(3)CO + O(2)--> OH +other products (1b) and CH(3)C(O)CH(2) + O(2)--> products (2) have been studied in isothermal discharge flow reactors with laser induced fluorescence monitoring of OH and CH(3)C(O)CH(2) radicals. The experiments have been performed at overall pressures between 1.33 and 10.91 mbar of helium and 298 +/- 1 K reaction temperature. OH formation has been found to be the dominant reaction channel for CH(3)CO + O(2): the branching ratio, Gamma(1b) = k(1b)/k(1), is close to unity at around 1 mbar, but decreases rapidly with increasing pressure. The rate constant of the overall reaction, k(2), has been found to be pressure dependent: the fall-off behaviour has been analysed in comparison with reported data. Electronic structure calculations have confirmed that at room temperature the reaction of CH(3)C(O)CH(2) with O(2) is essentially a recombination-type process. At high temperatures, the further reactions of the acetonyl-peroxyl adduct may yield OH radicals, but the most probable channel seems to be the O(2)-catalysed keto-enol transformation of acetonyl. Implications of the results for atmospheric modelling studies have been discussed.

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Section: Kinetics Of the Overall Reaction Of Ch 3 Co With Osupporting

confidence: 75%

Section: Oh Yield For the Reaction Of Ch 3 C(o) With Omentioning

confidence: 99%

Kinetics and mechanism of the reactions of CH3CO and CH3C(O)CH2 radicals with O2. Low-pressure discharge flow experiments and quantum chemical computations

Kovács

Zádor

Farkas

et al. 2007

Phys. Chem. Chem. Phys.

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“…However, based on MC-TST calculations incorporating all conformers, we found that thermal decomposition of the tri-HPACYL-I acyl radicals is still sufficiently fast to dominate over O 2 addition; i.e. even when assuming a Boltzmann energy distribution, the predicted rate coefficient of ∼ 2 × 10 8 s −1 at 300 K (see Table 3) is significantly higher than the effective O 2 addition rate for acyl radicals, experimentally measured at ≤∼ 3 × 10 7 s −1 in atmospheric conditions (Sehested et al, 1998;Blitz et al, 2002;Park et al, 2004; Baulch et al, 2005;Atkinson et al, 2006;Carr et al, 2011). One could counter that the presence of -OOH groups might stabilize the acylperoxy radicals formed in the O 2 addition (e.g.…”

Section: Elimination Of Co From Tri-hydroperoxy Acyl Radicalsmentioning

confidence: 68%

“…In addition, the submodel MEGAN (Model of Emissions of Gases and Aerosols from Nature) was used to simulate biogenic emissions of tracers, including isoprene (Guenther et al, 2006). Global isoprene emissions were scaled to 595 Tg yr −1 , which is the best estimate by Sindelarova et al (2014). The model was run for 1.5 years (summer 2011-2012), during which the first half-year was used as spin-up and 2012 was used for analysis.…”

Section: Global Modelmentioning

confidence: 99%

Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

et al. 2020

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Abstract. Theoretical, laboratory, and chamber studies have shown fast regeneration of the hydroxyl radical (OH) in the photochemistry of isoprene, largely due to unimolecular reactions which were previously thought not to be important under atmospheric conditions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospherically relevant NO levels (between 0.15 and 2 ppbv – parts per billion by volume) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to 1, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations, and the best agreement was observed when at least 50 % of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 ppbv. For these levels of NO, up to 50 % of the OH radicals are regenerated from the products of the 1,6 α-hydroxy-hydrogen shift (1,6-H shift) of Z-δ-RO2 radicals through the photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehydic hydrogen shift (rate constant ∼10 s−1 at 300 K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO2), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy, and organic peroxy radicals, carbon monoxide, and the sum of methyl vinyl ketone, methacrolein, and hydroxyl hydroperoxides) is nearly independent of the adopted yield of HPALD and di-HPCARP-RO2 as both degrade relatively fast (<1 h), forming the OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the distribution of oxygenated products, which affect radical levels and organic aerosol downwind of unpolluted isoprene-dominated regions.

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“…However, based on MC-TST calculations, incorporating all conformers, we found that thermal decomposition of the tri-HPACYL-I acyl radicals is still sufficiently fast to dominate over O 2 addition, i.e. even when assuming a Boltzmann energy distribution, the predicted rate coefficient of ~210 8 s -1 at 300 K (see Table 3), is significantly higher than the effective O 2 -addition rate for acyl radicals, experimentally measured at  ~310 7 s -1 in atmospheric conditions (Sehested et al, 1998;Blitz et al, 2002;Park et al, 2004;Baulch et al, 2005;Atkinson 285 et al, 2006;Carr et al, 2011). One could counter that the presence of -OOH groups might stabilize the acylperoxy radicals formed in the O 2 addition (e.g.…”

Section: Elimination Of Co From Tri-hydroperoxy Acyl Radicalsmentioning

confidence: 70%

Importance of isomerization reactions for the OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Novelli¹,

Vereecken²,

Dorn³

et al. 2019

Preprint

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Abstract. Theoretical, laboratory and chamber studies have shown fast regeneration of hydroxyl radical (OH) in the photochemistry of isoprene largely due to previously disregarded unimolecular reactions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in the isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospheric conditions (i.e. NO between 0.15 and 2&#8201;ppbv and temperature between 25 and 41&#8201;&#176;C) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to one, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations and the best agreement was observed when at least 50&#8201;% of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 parts per billion (ppbv). For these levels of NO, up to 50&#8201;% of the OH radicals are regenerated from the products of the 1,6 &#945;-hydroxy-hydrogen shift (1,6-H shift) of Z-&#948;-RO2 radicals through photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehyde hydrogen shift (rate constant &#8764;&#8201;10&#8201;s&#8722;1 at 300&#8201;K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO2), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy and organic peroxy radicals, carbon monoxide and the sum of methyl vinyl ketone, methacrolein and hydroxyl hydroperoxides) is nearly independent on the adopted yield of HPALD and di-HPCARP-RO2 as both degrade relatively fast (<&#8201;1&#8201;h), forming OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the oxygenated products distribution, which affect radical levels and organic aerosol downwind of unpolluted isoprene dominated regions.

show abstract

Absolute rate constants for F + CH3CHO and CH3CO + O2, relative rate study of CH3CO + NO, and the product distribution of the F + CH3CHO reaction

Cited by 29 publications

References 28 publications

Kinetics and mechanism of the reactions of CH3CO and CH3C(O)CH2 radicals with O2. Low-pressure discharge flow experiments and quantum chemical computations

Kinetics and mechanism of the reactions of CH3CO and CH3C(O)CH2 radicals with O2. Low-pressure discharge flow experiments and quantum chemical computations

Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Importance of isomerization reactions for the OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

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