Oxidation of toluene in NO? free air: Product distribution and mechanism

Seuwen, R.; Warneck, Peter

doi:10.1002/(sici)1097-4601(1996)28:5<315::aid-kin1>3.0.co;2-y

Cited by 51 publications

(52 citation statements)

References 15 publications

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“…The mechanistic yield of 20% for this compound comes close to experimental values published more recently by Klotz et al (1998) and Smith et al (1998). For benzaldehyde, the spread in literature yields is a factor of two and the model gives a yield of 6% that is supported by several studies published in the nineties by Klotz et al (1998), Bierbach et al (1994), and Seuwen and Warneck (1996). Literature values for the glyoxal yield vary between 8% and 39% (Atkinson, 1992;Volkamer et al, 2001 and references therein).…”

Section: Product Yieldsmentioning

confidence: 58%

Modelling of the photooxidation of toluene: conceptual ideas for validating detailed mechanisms

et al. 2003

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Abstract. Toluene photooxidation is chosen as an example to examine how simulations of smog-chamber experiments can be used to unravel shortcomings in detailed mechanisms and to provide information on complex reaction systems that will be crucial for the design of future validation experiments. The mechanism used in this study is extracted from the Master Chemical Mechanism Version 3 (MCM v3) and has been updated with new modules for cresol and γ -dicarbonyl chemistry. Model simulations are carried out for a toluene-NO x experiment undertaken at the European Photoreactor (EUPHORE). The comparison of the simulation with the experimental data reveals two fundamental shortcomings in the mechanism: OH production is too low by about 44%, and the ozone concentration at the end of the experiment is over-predicted by 55%. The radical budget was analysed to identify the key intermediates governing the radical transformation in the toluene system. Ring-opening products, particularly conjugated γ -dicarbonyls, were identified as dominant radical sources in the early stages of the experiment. The analysis of the time evolution of radical production points to a missing OH source that peaks when the system reaches highest reactivity. First generation products are also of major importance for the ozone production in the system. The analysis of the radical budget suggests two options to explain the concurrent under-prediction of OH and overprediction of ozone in the model: (1) missing oxidation processes that produce or regenerate OH without or with little NO to NO 2 conversion or (2) NO 3 chemistry that sequesters reactive nitrogen oxides into stable nitrogen compounds and at the same time produces peroxy radicals. Sensitivity analyCorrespondence to: M. J. Pilling (M.J.Pilling@chem.leeds.ac.uk sis was employed to identify significant contributors to ozone production and it is shown how this technique, in combination with ozone isopleth plots, can be used for the design of validation experiments.

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Section: Product Yieldsmentioning

confidence: 58%

Modelling of the photooxidation of toluene: conceptual ideas for validating detailed mechanisms

et al. 2003

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“…However, the detailed chemical mechanism of toluene oxidation in the atmosphere remains uncertain (4,5). Oxidation of toluene is initiated by the hydroxyl radical (OH): the initial OH−toluene reaction results in minor H abstraction (about 10%) and major OH addition (about 90%) (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The H-abstraction pathway leads to the formation of benzaldehyde, whose oxidative pathway is well established (4,5).…”

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confidence: 99%

Reassessing the atmospheric oxidation mechanism of toluene

Zhao

Terazono

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

189

122

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Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O2 to form the cresol proceeds with a smaller barrier than O2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.

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“…The latter are significantly less stable (owing to the loss of conjugation), but are included to provide a minor route to para-quinone products, which have been observed in some systems (e.g. Seuwen and Warneck, 1996;Berndt et al, 1999;Smith et al, 1999). These are therefore assigned a low probability of 10% in each case, with those formed from 1,2 addition being the dominant peroxy radical generated in each of the systems.…”

Section: Mechanisms To First Generation Productsmentioning

confidence: 99%

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds

et al. 2003

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Abstract. Kinetic and mechanistic data relevant to the tropospheric degradation of aromatic volatile organic compounds (VOC) have been used to define a mechanism development protocol, which has been used to construct degradation schemes for 18 aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). This is complementary to the treatment of 107 non-aromatic VOC, presented in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the degradation chemistry to first generation products via a number of competitive routes, and the further degradation of first and subsequent generation products. Emphasis is placed on describing where the treatment differs from that applied to the non-aromatic VOC. The protocol is based on work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Photochemical Ozone Creation Potentials (POCP) have been calculated for the 18 aromatic VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. These show distinct differences from POCP values calculated previously for the aromatics, using earlier versions of the MCM, and reasons for these differences are discussed.

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Oxidation of toluene in NO? free air: Product distribution and mechanism

Cited by 51 publications

References 15 publications

Modelling of the photooxidation of toluene: conceptual ideas for validating detailed mechanisms

Modelling of the photooxidation of toluene: conceptual ideas for validating detailed mechanisms

Reassessing the atmospheric oxidation mechanism of toluene

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds

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