Browsing by Author "Mentler, Bernhard"

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    Detection of RO2 radicals and other products from cyclohexene ozonolysis with NH4+ and acetate chemical ionization mass spectrometry
    (Oxford [u.a.] : Elsevier, 2018) Hansel, Armin; Scholz, Wiebke; Mentler, Bernhard; Fischer, Lukas; Berndt, Torsten
    The performance of the novel ammonium chemical ionization time of flight mass spectrometer (NH4+-CI3–TOF) utilizing NH4+ adduct ion chemistry to measure first generation oxidized product molecules (OMs) as well as highly oxidized organic molecules (HOMs) was investigated for the first time. The gas-phase ozonolysis of cyclohexene served as a first test system. Experiments have been carried out in the TROPOS free-jet flow system at close to atmospheric conditions. Product ion signals were simultaneously observed by the NH4+-CI3-TOF and the acetate chemical ionization atmospheric pressure interface time of flight mass spectrometer (acetate-CI-API-TOF). Both instruments are in remarkable good agreement within a factor of two for HOMs. For OMs not containing an OOH group the acetate technique can considerably underestimate OM concentrations by 2–3 orders of magnitude. First steps of cyclohexene ozonolysis generate ten different main products, detected with the ammonium-CI3-TOF, comprising 93% of observed OMs. The remaining 7% are distributed over several minor products that can be attributed to HOMs, predominately to highly oxidized RO2 radicals. Summing up, observed ammonium-CI3-TOF products yield 5.6 × 109 molecules cm−³ in excellent agreement with the amount of reacted cyclohexene of 4.5 × 109 molecules cm−³ for reactant concentrations of [O3] = 2.25 × 1012 molecules cm−³ and [cyclohexene] = 2.0 × 1012 molecules cm−³ and a reaction time of 7.9 s. NH4+ adduct ion chemistry is a promising CIMS technology for achieving carbon-closure due to the unique opportunity for complete detection of the whole product distribution including also peroxy radicals, and consequently, for a much better understanding of oxidation processes.
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    High Gas-Phase Methanesulfonic Acid Production in the OH-Initiated Oxidation of Dimethyl Sulfide at Low Temperatures
    (Columbus, Ohio : American Chemical Society, 2022) Shen, Jiali; Scholz, Wiebke; He, Xu-Cheng; Zhou, Putian; Marie, Guillaume; Wang, Mingyi; Marten, Ruby; Surdu, Mihnea; Rörup, Birte; Baalbaki, Rima; Amorim, Antonio; Ataei, Farnoush; Bell, David M.; Bertozzi, Barbara; Brasseur, Zoé; Caudillo, Lucía; Chen, Dexian; Chu, Biwu; Dada, Lubna; Duplissy, Jonathan; Finkenzeller, Henning; Granzin, Manuel; Guida, Roberto; Heinritzi, Martin; Hofbauer, Victoria; Iyer, Siddharth; Kemppainen, Deniz; Kong, Weimeng; Krechmer, Jordan E.; Kürten, Andreas; Lamkaddam, Houssni; Lee, Chuan Ping; Lopez, Brandon; Mahfouz, Naser G. A.; Manninen, Hanna E.; Massabò, Dario; Mauldin, Roy L.; Mentler, Bernhard; Müller, Tatjana; Pfeifer, Joschka; Philippov, Maxim; Piedehierro, Ana A.; Roldin, Pontus; Schobesberger, Siegfried; Simon, Mario; Stolzenburg, Dominik; Tham, Yee Jun; Tomé, António; Umo, Nsikanabasi Silas; Wang, Dongyu; Wang, Yonghong; Weber, Stefan K.; Welti, André; Wollesen de Jonge, Robin; Wu, Yusheng; Zauner-Wieczorek, Marcel; Zust, Felix; Baltensperger, Urs; Curtius, Joachim; Flagan, Richard C.; Hansel, Armin; Möhler, Ottmar; Petäjä, Tuukka; Volkamer, Rainer; Kulmala, Markku; Lehtipalo, Katrianne; Rissanen, Matti; Kirkby, Jasper; El-Haddad, Imad; Bianchi, Federico; Sipilä, Mikko; Donahue, Neil M.; Worsnop, Douglas R.
    Dimethyl sulfide (DMS) influences climate via cloud condensation nuclei (CCN) formation resulting from its oxidation products (mainly methanesulfonic acid, MSA, and sulfuric acid, H2SO4). Despite their importance, accurate prediction of MSA and H2SO4from DMS oxidation remains challenging. With comprehensive experiments carried out in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN, we show that decreasing the temperature from +25 to -10 °C enhances the gas-phase MSA production by an order of magnitude from OH-initiated DMS oxidation, while H2SO4production is modestly affected. This leads to a gas-phase H2SO4-to-MSA ratio (H2SO4/MSA) smaller than one at low temperatures, consistent with field observations in polar regions. With an updated DMS oxidation mechanism, we find that methanesulfinic acid, CH3S(O)OH, MSIA, forms large amounts of MSA. Overall, our results reveal that MSA yields are a factor of 2-10 higher than those predicted by the widely used Master Chemical Mechanism (MCMv3.3.1), and the NOxeffect is less significant than that of temperature. Our updated mechanism explains the high MSA production rates observed in field observations, especially at low temperatures, thus, substantiating the greater importance of MSA in the natural sulfur cycle and natural CCN formation. Our mechanism will improve the interpretation of present-day and historical gas-phase H2SO4/MSA measurements.