Browsing by Author "Scholz, Wiebke"
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- ItemDetection 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, TorstenThe 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.
- ItemHigh 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.
- ItemMeasurement report: Long-range transport and the fate of dimethyl sulfide oxidation products in the free troposphere derived from observations at the high-altitude research station Chacaltaya (5240ma.s.l.) in the Bolivian Andes(Katlenburg-Lindau : EGU, 2023) Scholz, Wiebke; Shen, Jiali; Aliaga, Diego; Wu, Cheng; Carbone, Samara; Moreno, Isabel; Zha, Qiaozhi; Huang, Wei; Heikkinen, Liine; Jaffrezo, Jean Luc; Uzu, Gaelle; Partoll, Eva; Leiminger, Markus; Velarde, Fernando; Laj, Paolo; Ginot, Patrick; Artaxo, Paolo; Wiedensohler, Alfred; Kulmala, Markku; Mohr, Claudia; Andrade, Marcos; Sinclair, Victoria; Bianchi, Federico; Hansel, ArminDimethyl sulfide (DMS) is the primary natural contributor to the atmospheric sulfur burden. Observations concerning the fate of DMS oxidation products after long-range transport in the remote free troposphere are, however, sparse. Here we present quantitative chemical ionization mass spectrometric measurements of DMS and its oxidation products sulfuric acid (H2SO4), methanesulfonic acid (MSA), dimethylsulfoxide (DMSO), dimethylsulfone (DMSO2), methanesulfinic acid (MSIA), methyl thioformate (MTF), methanesulfenic acid (MSEA, CH3SOH), and a compound of the likely structure CH3S(O)2OOH in the gas phase, as well as measurements of the sulfate and methanesulfonate aerosol mass fractions. The measurements were performed at the Global Atmosphere Watch (GAW) station Chacaltaya in the Bolivian Andes located at 5240m above sea level (a.s.l.). DMS and DMS oxidation products are brought to the Andean high-altitude station by Pacific air masses during the dry season after convective lifting over the remote Pacific ocean to 6000-8000ma.s.l. and subsequent long-range transport in the free troposphere (FT). Most of the DMS reaching the station is already converted to the rather unreactive sulfur reservoirs DMSO2 in the gas phase and methanesulfonate (MS-) in the particle phase, which carried nearly equal amounts of sulfur to the station. The particulate sulfate at Chacaltaya is however dominated by regional volcanic emissions during the time of the measurement and not significantly affected by the marine air masses. In one of the FT events, even some DMS was observed next to reactive intermediates such as methyl thioformate, dimethylsulfoxide, and methanesulfinic acid. Also for this event, back trajectory calculations show that the air masses came from above the ocean (distance >330km) with no local surface contacts. This study demonstrates the potential impact of marine DMS emissions on the availability of sulfur-containing vapors in the remote free troposphere far away from the ocean.