Mass spectrometric measurement of hydrogen isotope fractionation for the reactions of chloromethane with OH and Cl

• Verfasst von: Keppler, Frank [VerfasserIn]
• Verfasst von: Greule, Markus [VerfasserIn]
• Verfasst von: Schöler, Heinz Friedrich [VerfasserIn]
• Titel: Mass spectrometric measurement of hydrogen isotope fractionation for the reactions of chloromethane with OH and Cl
• Verf.angabe: Frank Keppler, Enno Bahlmann, Markus Greule, Heinz Friedrich Schöler, Julian Wittmer, Cornelius Zetzsch
• E-Jahr: 2018
• Jahr: 09 May 2018
• Umfang: 11 S.
• Fussnoten: Gesehen am 05.09.2019
• Titel Quelle: Enthalten in: Atmospheric chemistry and physics
• Ort Quelle: Katlenburg-Lindau : EGU, 2001
• Jahr Quelle: 2018
• Band/Heft Quelle: 18(2018), 9, Seite 6625-6635
• ISSN Quelle: 1680-7324
• DOI: doi:10.5194/acp-18-6625-2018
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1675992665

Abstract

<p><strong>Abstract.</strong> Chloromethane (CH<span class="inline-formula">₃</span>Cl) is an important provider of chlorine to the stratosphere but detailed knowledge of its budget is missing. Stable isotope analysis is a potentially powerful tool to constrain CH<span class="inline-formula">₃</span>Cl flux estimates. The largest degree of isotope fractionation is expected to occur for deuterium in CH<span class="inline-formula">₃</span>Cl in the hydrogen abstraction reactions with its main sink reactant tropospheric OH and its minor sink reactant Cl atoms. We determined the isotope fractionation by stable hydrogen isotope analysis of the fraction of CH<span class="inline-formula">₃</span>Cl remaining after reaction with hydroxyl and chlorine radicals in a 3.5&thinsp;m<span class="inline-formula">³</span> Teflon smog chamber at 293&thinsp;<span class="inline-formula">±</span>&thinsp;1&thinsp;K. We measured the stable hydrogen isotope values of the unreacted CH<span class="inline-formula">₃</span>Cl using compound-specific thermal conversion isotope ratio mass spectrometry. The isotope fractionations of CH<span class="inline-formula">₃</span>Cl for the reactions with hydroxyl and chlorine radicals were found to be <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">264</mn><mo>±</mo><mn mathvariant="normal">45</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="43b54b1a4760b2ad7bc64caa4dcf2d19"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-6625-2018-ie00001.svg" width="52pt" height="10pt" src="acp-18-6625-2018-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">280</mn><mo>±</mo><mn mathvariant="normal">11</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="62d70adff0e7afd0390fdc4d52c372b5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-6625-2018-ie00002.svg" width="52pt" height="10pt" src="acp-18-6625-2018-ie00002.png"/></svg:svg></span></span>&thinsp;‰, respectively. For comparison, we performed similar experiments using methane (CH<span class="inline-formula">₄)</span> as the target compound with OH and obtained a fractionation constant of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">205</mn><mo>±</mo><mn mathvariant="normal">6</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c22901eed2f7ed27e67c7076a8f4bad7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-6625-2018-ie00003.svg" width="46pt" height="10pt" src="acp-18-6625-2018-ie00003.png"/></svg:svg></span></span>&thinsp;‰ which is in good agreement with values previously reported. The observed large kinetic isotope effects are helpful when employing isotopic analyses of CH<span class="inline-formula">₃</span>Cl in the atmosphere to improve our knowledge of its atmospheric budget.</p>