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- Joelsson, L. M T, et al.
(författare)
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Kinetic isotope effects of 12CH3D+OH and 13CH3D+OH from 278 to 313K
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:7, s. 4439-4449
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Tidskriftsartikel (refereegranskat)abstract
- Methane is the second most important long-lived greenhouse gas and plays a central role in the chemistry of the Earth's atmosphere. Nonetheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including the doubly substituted species 13CH3D, offers new insight into the methane budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH in the troposphere, which accounts for around 84% of all methane removal. Here we present experimentally derived methane+OH kinetic isotope effects and their temperature dependence over the range of 278 to 313K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D Combining double low line 1.31 ± 0.01 and kCH4/k13CH3D Combining double low line 1.34 ± 0.03 at room temperature, implying that the methane+OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) Combining double low line kCH4/k13CH3D, within the experimental uncertainty, given the literature value of kCH4/k13CH4 Combining double low line 1.0039 ± 0.0002. In addition, the kinetic isotope effects were characterized using transition state theory with tunneling corrections. Good agreement between the experimental, quantum chemical, and available literature values was obtained. Based on the results we conclude that the OH reaction (the main sink of methane) at steady state can produce an atmospheric clumped isotope signal (δ(13CH3D) Combining double low line ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02. This implies that the bulk tropospheric δ(13CH3D) reflects the source signal with relatively small adjustment due to the sink signal (i.e., mainly OH oxidation).
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- Heimdal Nilsson, Elna, et al.
(författare)
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Re-evaluation of the reaction rate coefficient of CH3Br + OH with implications for the atmospheric budget of methyl bromide
- 2013
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 80, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- The reaction rate coefficient k(CH3Br + OH) has been determined in the temperature range 298-373 K, using pulse radiolysis/UV kinetic spectroscopy, and at 298 K using a relative rate method. The Arrhenius expression obtained from a fit to the experimental results is (2.9 +/- 0.9) x 10(-12) exp(-(1230 +/- 125)/T) cm(3) molecule(-1) s(-1), which is greater than the expression currently recommended. The relative rate experiments give k(298 K) = (4.13 +/- 0.63) x 10(-14) cm(3) molecule(-1) s(-1). The results of the absolute and relative rate experiments indicate that the source budget of atmospheric CH3Br should be reinvestigated, as was recently done for CH3Cl. (C) 2013 Elsevier Ltd. All rights reserved.
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- Joelsson, L. M. T., et al.
(författare)
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Relative rate study of the kinetic isotope effect in the (CH3D)-C-13 + Cl reaction
- 2014
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 605, s. 152-157
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Tidskriftsartikel (refereegranskat)abstract
- The (CH3D)-C-13/(CH4)-C-12 kinetic isotope effect, alpha((CH3D)-C-13), of CH4 + Cl is determined for the first time, using the relative rate technique and Fourier transform infrared (FTIR) spectroscopy. alpha((CH3D)-C-13) is found to be 1.60 +/- 0.04. In addition, a quantum chemistry/transition state theory model with tunneling correction is constructed and the primary cause for alpha((CH3D)-C-13) is found to be the substantially reduced reactivity of the D atom, which, in turn, can be explained by a significant increase in the reaction barrier due to changes in the vibrational zero point energy and to a lesser extent tunneling. (C) 2014 Elsevier B.V. All rights reserved.
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- Joelsson, L. M.T., et al.
(författare)
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Tailored reduced kinetic mechanisms for atmospheric chemistry modeling
- 2019
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 213, s. 675-685
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Tidskriftsartikel (refereegranskat)abstract
- Reduced chemical kinetic mechanisms are essential for atmospheric chemistry modeling where the use of explicit kinetic schemes is too computationally demanding. By tailoring mechanisms to specific cases, the size of the mechanism can be kept small, without significant loss of accuracy in predictions of selected species’ concentrations. In the present work, we present small kinetic mechanisms tailored to specific cases, using a novel method. The reduced mechanisms are generated by applying the method to several cases previously described in the literature and their performance in box model simulations are evaluated. The characteristics of the reduced mechanisms are examined. In addition, the method's sensitivity towards time scales, choice of trace gas species of interest, and NOx regime are investigated. The reduced mechanisms include 10%–30% of all the reactions in the relevant subset of the detailed chemical mechanism. Simulations with the reduced mechanisms typically yield no loss in accuracy of ozone concentration predictions and less than a 10% accuracy loss for the concentration predictions of nitrogen oxides for the cases over as long as five simulated days. Mechanisms generated to predict the concentrations of few species, over short time scales, in high NOx conditions, and with no isoprene, generally include fewer reactions than mechanisms generated to predict the concentrations of several species, over long time scales, in lowNOx, isoprene rich conditions.
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